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CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
Hello all, just purchased a new quickfuel 750 DP and am going to go down the road of tuning. I currently have a 670 street avenger that I followed SOfkingdoms guide and am very happy with the result. However I really wanted the mech secondary and maybe a few more ponies so I sprung for a new carb for my freshly rebuilt 383 stroker. I also just purchased a AEM AFR gauge and wanted to monitor what the 670 is doing as the out of the box 750 was not good. So my questions for sofaking is that on very light throttle I am very lean between 14.5 to 16.5 range +/- and once I hit the gas a bit it drops right to the 13.5 rage, which is what I am assuming is the reason for the higher hg power valve (I am running a 10.5). Is this normal and what I should be aiming for with the new carb? There is no hesitation or issues currently but I have read this lean condition is dangerous for the engine for detonation but again once any gas or load is applied it is in the correct range.
EDIT: Due to logistics I had to put my O2 bung further downstream of the header collector on the y-pipe by about 18", this may cause a slightly leaner read on my AFR gauge but according to Engine Masters, there should be no difference.
This forum is great!
Last edited by caddyescalade; 05-13-2024 at 04:47 PM.
Further to this. I also only have 10-11hg of vacuum at idle so if I put that 10.5 power valve in my new 750 DP am I going to see this dumping in fuel at idle? Does your idle vacuum not impact what powevalve to select?
Further to this. I also only have 10-11hg of vacuum at idle so if I put that 10.5 power valve in my new 750 DP am I going to see this dumping in fuel at idle? Does your idle vacuum not impact what powevalve to select?
While we wait for Mr S to chime in, I can offer some experiences as well as direct to you some dialogue with guys that tune these carbs professionally.
The PV, even if open, will not affect the idle. Idle meaning that the throttle blades are closed. It's only in throttle positions above idle that the PV circuit is active.
I've demonstrated this to myself while tuning my own carb.
Forget the 2" more than idle vacuum PV thinking. Recommended by Holley perhaps but that's to keep people from going on a misadventure.
FTR: my PV tuning procedure involves an AFR gauge (as you have) but I also have a in-cabin mounted manifold vacuum gauge.
I've 9-10" of idle vacuum and an 8.5 PV but that 8.5 wasn't based on a suggestion but rather what I observed while cruising (high vacuum well above 8.5") and the part throttle acceleration. I ended up with that 8.5 valve because under moderate acceleration, such as to pass but not pinned, I saw where the manifold fell to less than 9". So, under the right condition and throttle pressure, I could initiate the PV function and observe the AFRs fattening up. It behaves like another passing gear. From my lean cruise of 15:1 or better (which is also deliberate) to 13:1.
The effect is remarkable without WOT or in my case, initiating the vacuum secondaries (or in your case, further opening of the secondaries more than needed).
Interesting for sure. I will start following Sofkingdoms Holley tuning guide from the beginning with this new carb. SInce I have an AFR gauge I was just looking for some input on where the number should be in various situations. I dropped a couple of jets and tried it out of the box, needed a larger squirter to get rid of a major stumble, for which that fixed. I did notice when I driving around its currently a bit rich in the high 12ish range, but when I put it to the floor the gauge is pinned right down and bottoms out at the lowest under 8.5. SO I know I'm very rich at wide open, not sure where that value should be with a mechanical secondary carb. I'll do some research with tuning a carb with an AFR gauge to see if I can some insight as to where the numbers should be at.
So yourself a favor and get a vacuum in the interior.
You'll find it immensely helpful.
If I may ask, do you know what your jetting is now?
How about the idle air bleeds and high speed air bleeds?
These go a step beyond Sofa's sticky, however they may come into play as you go.
If kingdom doesn't come through I can direct you to a source of information that is at least overwhelming. At best, immensely helpful.
Good luck.
Disclaimer: I've never had, or used, a WBO2 for tuning. Which is to say, it's not my custom to interpret their readings. We simply didn't have any such thing when I was learning, so, we relied on ... more crude ... indicators of engine "happiness".
One thing we always concerned ourselves with was, what mattered at the moment, in the context of what was expected of the vehicle. Sort of, "mind over matter": if you don't mind, it don't matter. So, before I'd even get worked up about it at all, I'd wonder whether the car runs poorly at any of these times. If it's OK, then leave it alone. OTOH if it stumbles or sputters or whatever in those light throttle situations, then proceed further.
In a Holley, the power valve itself, doesn't have any calibration available, other than its opening point. That is, unless you're into soldering up and re-drilling orifices, it's more of just a switch: power, no-power. Yes/no. You don't really have any control over "how much". That's built into the carb. I don't know much about QF carbs but I suspect they're much the same.
You say, on light throttle you're lean. Is your gauge fast enough to tell you, is the mixture OK for a time, then after some period, goes lean? Or, does it immediately go lean on throttle tip-in? The first condition points to a main system issue: fuel level too low, wrong choice of boosters, main air bleeds. The 2nd points toward the transition system. Assuming of course, that the QF carb duplicates the Holley design in both areas.
If it was a Holley I think the first thing I'd try is raising the fuel level a bit. My usual method of setting a Holley is to get it where it doesn't dribble out of the plug, but rather takes a pretty good bump on the fender to spill any fuel. Wherever yours is now, try raising it to where it takes ALOT less of a bump on the fender to make any spill out. Note that this will make EVERYTHING richer; but in all likelihood, the only change you may have to make, is the jets; and those, probably only a .001" or 2.
Next thing I'd try is raising the PV number. Since its effect on idle is minimal, you may be in the situation where idle vacuum is quite low due to your cam and idle speed settings, but cruising or other actual operating vacuum may be substantially higher. Knowing the vacuum under those conditions will spare you some trial-and-error.
So yourself a favor and get a vacuum in the interior.
You'll find it immensely helpful.
If I may ask, do you know what your jetting is now?
How about the idle air bleeds and high speed air bleeds?
These go a step beyond Sofa's sticky, however they may come into play as you go.
If kingdom doesn't come through I can direct you to a source of information that is at least overwhelming. At best, immensely helpful.
Good luck.
my jetting is a 70 in the primary (factory 72) and secondary is a 78 (factory 80). Not sure what the idle air and high speed bleeds are but the outer is 70 and the inner is 31 according to the website.
How is the best way to get my full thottle AFR leaner? Dropping the secondary jet a couple more sizes?
I don’t have a vacuum gauge inside but that isn’t very difficult for me to do.
Disclaimer: I've never had, or used, a WBO2 for tuning. Which is to say, it's not my custom to interpret their readings. We simply didn't have any such thing when I was learning, so, we relied on ... more crude ... indicators of engine "happiness".
One thing we always concerned ourselves with was, what mattered at the moment, in the context of what was expected of the vehicle. Sort of, "mind over matter": if you don't mind, it don't matter. So, before I'd even get worked up about it at all, I'd wonder whether the car runs poorly at any of these times. If it's OK, then leave it alone. OTOH if it stumbles or sputters or whatever in those light throttle situations, then proceed further.
In a Holley, the power valve itself, doesn't have any calibration available, other than its opening point. That is, unless you're into soldering up and re-drilling orifices, it's more of just a switch: power, no-power. Yes/no. You don't really have any control over "how much". That's built into the carb. I don't know much about QF carbs but I suspect they're much the same.
You say, on light throttle you're lean. Is your gauge fast enough to tell you, is the mixture OK for a time, then after some period, goes lean? Or, does it immediately go lean on throttle tip-in? The first condition points to a main system issue: fuel level too low, wrong choice of boosters, main air bleeds. The 2nd points toward the transition system. Assuming of course, that the QF carb duplicates the Holley design in both areas.
If it was a Holley I think the first thing I'd try is raising the fuel level a bit. My usual method of setting a Holley is to get it where it doesn't dribble out of the plug, but rather takes a pretty good bump on the fender to spill any fuel. Wherever yours is now, try raising it to where it takes ALOT less of a bump on the fender to make any spill out. Note that this will make EVERYTHING richer; but in all likelihood, the only change you may have to make, is the jets; and those, probably only a .001" or 2.
Next thing I'd try is raising the PV number. Since its effect on idle is minimal, you may be in the situation where idle vacuum is quite low due to your cam and idle speed settings, but cruising or other actual operating vacuum may be substantially higher. Knowing the vacuum under those conditions will spare you some trial-and-error.
The brawler has site glasses so I’m set to just over 1/2 way up. This is made by Holley and From what I’ve been told is the same just made in china. I cannot confirm this but all parts are interchangeable.
I’ll extend the vacuum gauge to inside for tuning and go from there.
Each situation is unique which is no surprise I'm sure.
But when jetting, go for a real cause and effect. Four sizes in one direction at a minimum.
Both ends of the carb have an impact on the WOT AFRs but if your cruise with minimal throttle opening is OK (so that the secondaries aren't much in play depending on the front to back ratio) then go for the secondary side to start.
There are other elements too such as the power valve channel restriction (PVCR) which helps to determine how much influence the PV has on enrichment but that's deeper into the tune should you need it.
In summary, go 4 sizes on the secondary and see where that takes you.
As for the vacuum gauge, your moderate acceleration and how the PV interacts under those conditions (load vs RPM) will be very observable with the gauge available.
Each situation is unique which is no surprise I'm sure.
But when jetting, go for a real cause and effect. Four sizes in one direction at a minimum.
Both ends of the carb have an impact on the WOT AFRs but if your cruise with minimal throttle opening is OK (so that the secondaries aren't much in play depending on the front to back ratio) then go for the secondary side to start.
There are other elements too such as the power valve channel restriction (PVCR) which helps to determine how much influence the PV has on enrichment but that's deeper into the tune should you need it.
In summary, go 4 sizes on the secondary and see where that takes you.
As for the vacuum gauge, your moderate acceleration and how the PV interacts under those conditions (load vs RPM) will be very observable with the gauge available.
Hope that helps.
yea thank you! I’ll try it. I did increase the squirter nozzle from 31 to 35 which helped with a bad off idle stumble. I’m thinking I need to hold WOT for a while to monitor the AFR gauge. I’m assuming with the nozzle and the accelerator pump on a double pumper it’s going to be rich at WOT as they are setup like that to avoid stumble. Then I’m assuming the mixture will start leaning out. Again just a guess here.
I’ve put a 76 jet in the secondary, 10.5 power valve and a 70 primary jet. I’ll see how it works tomorrow and I’ll bring my vacuum gauge with me.
Quick question: IIRC Sofas tuning sticky references the transfer slot (both primary and secondary) and to be sure it has the correct "exposure" with the blades closed against the idle stop screws. Too much of the slot exposed will cause a noticeable stumble when accelerating just off idle.
Often what happens, in an attempt to get the idle speed correct, is the the idle stop screw is screwed in further so as to open the butterflies a little more. This will ruin the t-slot exposure setting. There's that stumble.
Another question: Have you confirmed your timing? Idle. Full mechanical. Vacuum advance. These will all play a part in the drivability. Often a carb issue can be traced back to inadequate timing.
Quick question: IIRC Sofas tuning sticky references the transfer slot (both primary and secondary) and to be sure it has the correct "exposure" with the blades closed against the idle stop screws. Too much of the slot exposed will cause a noticeable stumble when accelerating just off idle.
Often what happens, in an attempt to get the idle speed correct, is the the idle stop screw is screwed in further so as to open the butterflies a little more. This will ruin the t-slot exposure setting. There's that stumble.
Another question: Have you confirmed your timing? Idle. Full mechanical. Vacuum advance. These will all play a part in the drivability. Often a carb issue can be traced back to inadequate timing.
thanks for the reply. All of these things did not happen with my old Holley 670 street avenger with vacuum secondaries. Therefore timing is not an issue. I will dig deeper into the transfer slot. When I take the carb off again
Quick question: IIRC Sofas tuning sticky references the transfer slot (both primary and secondary) and to be sure it has the correct "exposure" with the blades closed against the idle stop screws. Too much of the slot exposed will cause a noticeable stumble when accelerating just off idle.
Often what happens, in an attempt to get the idle speed correct, is the the idle stop screw is screwed in further so as to open the butterflies a little more. This will ruin the t-slot exposure setting. There's that stumble.
Another question: Have you confirmed your timing? Idle. Full mechanical. Vacuum advance. These will all play a part in the drivability. Often a carb issue can be traced back to inadequate timing.
so I did some more messing and have gotten it running pretty good. Oddly I had the idle circuit seemingly tuned fine but when I pulled the carb off to check the transfer slot exposure and it was closed right off. So I backed the little screw off to close the secondary blades completely and then set the transfer slot to the bare minimum exposure on the primaries which was about .030 or less. The car was still idling a bit high. So it appears that if I set the idle how I like it it closes the transfer slot too much. The only thing I found that could lower the idle was to change from manifold to ported on the vacuum advance, which worked but it is not ideal.
is they another way to slightly drop my idle speed without closing the primary blades any more?
I have an AED HO 950 on a ZZ502. I set the primaries for the correct idle slot exposure. I adjust the idle RPM on the secondary side, never touching the primary idle speed adjustment after the first setting. That does result in barely any idle slot on the secondary side, but that's OK.
so I did some more messing and have gotten it running pretty good. Oddly I had the idle circuit seemingly tuned fine but when I pulled the carb off to check the transfer slot exposure and it was closed right off. So I backed the little screw off to close the secondary blades completely and then set the transfer slot to the bare minimum exposure on the primaries which was about .030 or less. The car was still idling a bit high. So it appears that if I set the idle how I like it it closes the transfer slot too much. The only thing I found that could lower the idle was to change from manifold to ported on the vacuum advance, which worked but it is not ideal.
is they another way to slightly drop my idle speed without closing the primary blades any more?
With your vacuum advance sourced from manifold vacuum, what's your timing?
I have an AED HO 950 on a ZZ502. I set the primaries for the correct idle slot exposure. I adjust the idle RPM on the secondary side, never touching the primary idle speed adjustment after the first setting. That does result in barely any idle slot on the secondary side, but that's OK.
Don
Williamsburg.
One feature of the Barry Grant 750 VS I have is an idle air bypass. They call it Idle-Eaze which is essentially the same as drilling a couple of holes in the butterflies. That's the old school remedy for big cammed engines that need the throttles open too much to achieve a high enough idle speed.
As for the secondary idle adjustment, some old Holley's (IIRC) had a set screw that had to accessed from below in order to move the secondary blades. That was truly a PITA.
Concerning the OP, I can't say I've come across his particular problem unless there was an undetected vacuum leak somewhere.
I removed the secondary adjustment screw and installed a cap screw with a locking nut. I can use an allen wrench to adjust the idle speed on the secondary and lock it down with the lock nut.
another way to slightly drop my idle speed without closing the primary blades any more?
Check for vacuum leaks. Remove every vacuum line from the carb and plug the fittings; spray carb cleaner (NOT Brakleen) around gaskets, esp the carb <–> intake one; etc.
Check for vacuum leaks. Remove every vacuum line from the carb and plug the fittings; spray carb cleaner (NOT Brakleen) around gaskets, esp the carb <–> intake one; etc.
With your vacuum advance sourced from manifold vacuum, what's your timing?
not really sure what the advance gives it. The correct way is to set the timing with vacuum advances plugged. I’d be somewhere in the 16 BTDC, with about 36 BTDC total timing .
not really sure what the advance gives it. The correct way is to set the timing with vacuum advances plugged. I’d be somewhere in the 16 BTDC, with about 36 BTDC total timing .
Is that saying that you've got 16° initial and the vacuum can adds another 20?
Or is that 36° total timing with the mechanical advance all in (16 initial and 20 mechanical) plus whatever the vacuum adds?
Is that saying that you've got 16° initial and the vacuum can adds another 20?
Or is that 36° total timing with the mechanical advance all in (16 initial and 20 mechanical) plus whatever the vacuum adds?
yes to the 2nd one 16 initial and 36 total with vacuum advance unplugged. Haven’t recorded what it’s doing with the vacuum advance hooked up.
Ok.
My angle on that is a possible contributor to the high idle (other than the aforementioned vacuum leak). Having the vacuum advance connected to the manifold did wonders for my over-cammed and worn out 355's idle. But the maximum idle advance I ran was close to 30°.
16 initial plus 14 from the vacuum can.
Vac adv is usually somewhere in the 12° range; maybe up to 15°. Skinny's 14 is pretty normal.
Only problem with using full vac for the adv is, if the idle vac ever drops below the can's setting. If that happens, the extra adv goes away, and the engine will probably die immediately.
Only problem with using full vac for the adv is, if the idle vac ever drops below the can's setting. If that happens, the extra adv goes away, and the engine will probably die immediately.
I'll admit that tuning around that was a real dance.
I'd started with an adjustable can as well as a limiting plate in the distributor.
Worked it until (in my case) the can was "all in" about 2" below idle vacuum. Idled at 9", can was done at 7".
Ultimately, I found a can that had both the correct onset point as well as amount. A B5(?) comes to mind but I could be mistaken.
It'd be difficult In a stick car with the revs being pulled down with clutch engagement but an auto with a loose converter makes it much easier.
EDIT: Nope. Not B5.
I'll admit that tuning around that was a real dance.
I'd started with an adjustable can as well as a limiting plate in the distributor.
Worked it until (in my case) the can was "all in" about 2" below idle vacuum. Idled at 9", can was done at 7".
Ultimately, I found a can that had both the correct onset point as well as amount. A B5(?) comes to mind but I could be mistaken.
It'd be difficult In a stick car with the revs being pulled down with clutch engagement but an auto with a loose converter makes it much easier.
EDIT: Nope. Not B5.
Mine is a manual car as well. I’d prefer to not mess with the timing right now unless I have to as it just adds another element.
I did more more messing tonight and couldn’t find a vacuum leak. Rpm at idle is ok when I run the vacuum advance as ported which isn’t the end of the world. Just odd that it idles too high with vacuum advance connected to manifold vacuum. This did not happen until I set the primary blades to have the correct amount of transition slot. And my old 670 carb was the opposite and had too much transition slot showing but the car idled fine. I can live with it off the ported vacuum, just is odd.
Dropped another jet size both primary and secondary. Took the car for a ride and it seems ok, AFR reading seem to vary from very light throttle around 15 down to 12-13 when adding say 1/2 throttle. But when I punch it at wot it doesn’t seem to have much jam and immediately the AFR drops way rich for a couple seconds to like 8.8 and then starts climbing up to around 12 or so as I build rpms and it starts pulling good. So im guessing im going super rich off the initial punch from the squirters and both accelerator pumps shooting gas to avoid stumble due to the mechanical secondaries. There is no stumble or miss or cough, just not a lot of pull until the rpm’s go up and start leaning out.
so far I’ve went on the jets from a primary stock 72 to a 67 and a secondary stock 80 way down to a 71. Power valve is 8.5. I’m scared I’m too lean, not too sure what to think as the afr is still reading rich if anything.
bottom line so far is the 750 dp seems to rev higher and seem better on high rpm but seems to have quite a bit less torque than the 670 street avenger with vacuum secondary. Maybe that is normal? I’m new to this.
Regarding the idle RPM between ported vs manifold vacuum advance. That would be expected. Manifold vacuum is allowing for vacuum advance so you're gaining some timing and with that some RPM. With a ported source, the vacuum canister is seeing zero vacuum so no advance.
As for carb tuning, what area of the AFR curve have you tackled first?
Generally, I would settle on a comfortable cruise mixture. Sorting that out via the primary side and depending on the linkage ratio between front and back, to a lesser extent the secondary side. Vacuum secondaries are easier (to me) in that regard. Part throttle acceleration, after a good cruise is achieved, for me, is tailored via the PV. I want that to open when the throttles are opened enough vs load vs the manifold vacuum seen.
WOT is the domain of the secondary side.
Now, as with everything, there are other ways to go about it but that's been my approach and have had good results.
Regarding the idle RPM between ported vs manifold vacuum advance. That would be expected. Manifold vacuum is allowing for vacuum advance so you're gaining some timing and with that some RPM. With a ported source, the vacuum canister is seeing zero vacuum so no advance.
As for carb tuning, what area of the AFR curve have you tackled first?
Generally, I would settle on a comfortable cruise mixture. Sorting that out via the primary side and depending on the linkage ratio between front and back, to a lesser extent the secondary side. Vacuum secondaries are easier (to me) in that regard. Part throttle acceleration, after a good cruise is achieved, for me, is tailored via the PV. I want that to open when the throttles are opened enough vs load vs the manifold vacuum seen.
WOT is the domain of the secondary side.
Now, as with everything, there are other ways to go about it but that's been my approach and have had good results.
I’ve had good success so far, just seem to keep dropping jets then I encounter other issues along the way like erratic fuel pressure all of a sudden.
also for the life of me I can’t understand why when my car sits overnight and I go to start it the next day it is completely flooded. Blows black moisture out the pipes, smokes and takes a few seconds to burn itself off. What could be causing the car to flood after shut down? Brawler carburetor is new, other than I keep taking the bowls off to adjust getting and replace power valve, adjust transition slot exposure etc.
I’ve had good success so far, just seem to keep dropping jets then I encounter other issues along the way like erratic fuel pressure all of a sudden.
also for the life of me I can’t understand why when my car sits overnight and I go to start it the next day it is completely flooded. Blows black moisture out the pipes, smokes and takes a few seconds to burn itself off. What could be causing the car to flood after shut down? Brawler carburetor is new, other than I keep taking the bowls off to adjust getting and replace power valve, adjust transition slot exposure etc.
has anyone seen this nonsense?
Fuel pressure?
Would you list your tank, pump, regulator, PSI at the carb? Could be as simple as a FUBARED needle and seat.
If you have an electric pump and a fuel pump safety switch, you may want to check the FP safety switch. It is supposed to stop the pump from running when there is no oil pressure. They are normally on the Battery circuit and will run 24/7 if that safety switch goes out, even without a key on condition.
Fuel pressure?
Would you list your tank, pump, regulator, PSI at the carb? Could be as simple as a FUBARED needle and seat.
factory 86 gas tank, brand new edelbrock mechanical fuel pump I just bought today to try and fix this and after installing it is only putting out 4 psi with regulator Bypassed or fully open. It is rated for 6 psi.
A quick bit of history, I broke down yesterday on a short bag drive after messing with my carb, car went super lean and then died like it ran out of gas. Fuel pressure gauge at zero and the floats empty. Had to tow it home. Then it fired right up after priming the carb and seemed to run fine again. I figured fuel pump issue. Replaced it today and still very low psi. Fuel psi has been very erratic over recent days.
Im assuming im dealing with 2 different problems here.
the flooding after I shut the car down could be a needle and seat issue? How do I check that?
I have sight glasses so I know the floats seem to be working.
Last edited by caddyescalade; 06-04-2024 at 08:07 AM.
The pump is new and there was no change in the running condition?
Is the fuel filter fresh?
The operation of the pump is a simple deal. Not much to go wrong there but you should check the output. Pull off the inlet to the carb and let is discharge into a pail. You'll get a sense of the volume and whether it appears adequate or not. The fuel in the bowls will keep it running for a minute or so.
Another test is to ensure the fuel pump eccentric on the cam hasn't started going away. It happened to me. With the pump removed but the pushrod still in place, cranking the engine over (disable the ignition) will see the pushrod move in and out about a 1/2". Keep your finger against it so it maintains contact with the cam. If it's noticeably less than a 1/2", that's trouble.
Below is what mine looked like.
Fresh filter and fuel in the tank and you should be able to observe the bowls maintaining the proper level.
The flooding....other than the fuel boiling when you shut it down, you got me on that one.
Before it's started the next time when the "flooding" is likely to occur, pull the air filter and examine the carb for signs of excess fuel. It shouldn't flood on its own if the float levels were ok previously.
Vac adv is usually somewhere in the 12° range; maybe up to 15°. Skinny's 14 is pretty normal.
Only problem with using full vac for the adv is, if the idle vac ever drops below the can's setting. If that happens, the extra adv goes away, and the engine will probably die immediately.
Originally Posted by skinny z
I'll admit that tuning around that was a real dance.
I'd started with an adjustable can as well as a limiting plate in the distributor.
Worked it until (in my case) the can was "all in" about 2" below idle vacuum. Idled at 9", can was done at 7".
Ultimately, I found a can that had both the correct onset point as well as amount. A B5(?) comes to mind but I could be mistaken.
It'd be difficult In a stick car with the revs being pulled down with clutch engagement but an auto with a loose converter makes it much easier.
EDIT: Nope. Not B5.
B28 vacuum canister. L79 Vettes of the mid 60's are one of the applications.
All in between 6-8". 14° total comes to mind although I may still have the Crane advance limiter plate in the distributor.
Engine idles at 9.5-10" so that can for that engine worked well.
The pump is new and there was no change in the running condition?
Is the fuel filter fresh?
The operation of the pump is a simple deal. Not much to go wrong there but you should check the output. Pull off the inlet to the carb and let is discharge into a pail. You'll get a sense of the volume and whether it appears adequate or not. The fuel in the bowls will keep it running for a minute or so.
Another test is to ensure the fuel pump eccentric on the cam hasn't started going away. It happened to me. With the pump removed but the pushrod still in place, cranking the engine over (disable the ignition) will see the pushrod move in and out about a 1/2". Keep your finger against it so it maintains contact with the cam. If it's noticeably less than a 1/2", that's trouble.
Below is what mine looked like.
Fresh filter and fuel in the tank and you should be able to observe the bowls maintaining the proper level.
The flooding....other than the fuel boiling when you shut it down, you got me on that one.
Before it's started the next time when the "flooding" is likely to occur, pull the air filter and examine the carb for signs of excess fuel. It shouldn't flood on its own if the float levels were ok previously.
Good advice. Cam is new, so I hope it isn’t that. I’m going to start with a fuel line directly into a Jerry can to the pump and monitor the pressure to eliminate the gas tank and fuel line as being a problem. Yes I have a new fuel filter, fuel pump.
I will fix one problem before dealing with another I suppose. Thanks again. I’ll try to monitor what it’s doing more closely at shut off and restart. Maybe I’ll eliminate the choke as a potential issue as well.
There are not very many ways that fuel can get into the manifold with the engine off and the fuel pump not running. Since it is a mechanical pump, the FP running is not a potential issue. It's got to be some gravity draining the fuel bowls. If it was mine, I would change the gaskets on the bowls and metering blocks. I would fill the bowls manually (through the vent tubes or run the fuel pump to fill the bowls to the proper level in the site glass. Without draining the bowls, I would lift the carb and put a piece of cardboard under it (between the carb and manifold). Wait and look for evidence of leakage.
not very many ways that fuel can get into the manifold with the engine off and the fuel pump not running.
Actually, there is ONE, that I detailed in the OP's other post. It's by way of the fuel in the carb, boiling. Specifically, because he has a returnless fuel pump, with unknown connection to the (hot) engine block.
Which is not to say, "carb gaskets don't go bad", "a carb gasket can't cause this", "don't bother with carb gaskets", or ANYTHING ELSE of the kind; only, that carb gaskets are BY FAR not the only, or even the highest probability, cause of the behavior at hand.
Last edited by sofakingdom; 06-04-2024 at 07:00 PM.
Actually, there is ONE, that I detailed in the OP's other post. It's by way of the fuel in the carb, boiling. Specifically, because he has a returnless fuel pump, with unknown connection to the (hot) engine block.
Which is not to say, "carb gaskets don't go bad", "a carb gasket can't cause this", "don't bother with carb gaskets", or ANYTHING ELSE of the kind; only, that carb gaskets are BY FAR not the only, or even the highest probability, cause of the behavior at hand.
Great advice everyone! I’ll test and report back .
The pump is new and there was no change in the running condition?
Is the fuel filter fresh?
The operation of the pump is a simple deal. Not much to go wrong there but you should check the output. Pull off the inlet to the carb and let is discharge into a pail. You'll get a sense of the volume and whether it appears adequate or not. The fuel in the bowls will keep it running for a minute or so.
Another test is to ensure the fuel pump eccentric on the cam hasn't started going away. It happened to me. With the pump removed but the pushrod still in place, cranking the engine over (disable the ignition) will see the pushrod move in and out about a 1/2". Keep your finger against it so it maintains contact with the cam. If it's noticeably less than a 1/2", that's trouble.
Below is what mine looked like.
Fresh filter and fuel in the tank and you should be able to observe the bowls maintaining the proper level.
The flooding....other than the fuel boiling when you shut it down, you got me on that one.
Before it's started the next time when the "flooding" is likely to occur, pull the air filter and examine the carb for signs of excess fuel. It shouldn't flood on its own if the float levels were ok previously.
so I have a couple issues here. Regarding the fuel pump I just did a bunch of testing and I’m no more ahead. Fed the pump with a Jerry can and hose, still only 4 ish psi. Checked flow and it appears to be moving lots of gas although the suction seems very weak but maybe that is normal as it did suck and flow gas. Tried 2 different gauges and lines, removed regulator and ran direct. All appear to be same low psi issue. Good news is that my test should eliminate the gas tank and fuel line being bad. Bad news is I don’t know what is left other than not enough push from the cam. So bad rod or wire our lobe? Like I said cam is new so I really can’t see it but idk. Maybe I need a different push rod. I’ll remove everything and see.
I also did check sofakingdoms suggestion and it is just a short bolt in the front.
The other odd element to this is it did die on me and not pump any gas and had zero fuel pressure with the other fuel pump. Then it seemed to work again when cooled down. That’s why I switched fuel pumps. If it was a bad lobe or rod it wouldn’t work I intermittently. I’m stumped.
id hate to go with an electric fuel pump after all this time and money replacing and troubleshooting with this one.
"The other odd element to this is it did die on me and not pump any gas and had zero fuel pressure with the other fuel pump. Then it seemed to work again when cooled down."
Yet again, addressed in the OP's other post about this, where installing a fuel pump with a return was recommended, since it keeps the fuel in the suction side of the system so much cooler.
4 psi is fine. Entirely enough. About what a stock pump provides, which was enough for the 400 engine I had in my 83. Big solid lifter cam, Holley 800, etc.
I can't suggest strongly enough, get rid of all that ... stuff ... like Edelbrock pump, regulator, etc.; and put it back stock. Stock pump, good quality pressure line from pump to carb, hook up the return line. Probably will work FAR better. Certainly was more than adequate in mine.
Yet again, addressed in the OP's other post about this, where installing a fuel pump with a return was recommended, since it keeps the fuel in the suction side of the system so much cooler.
4 psi is fine. Entirely enough. About what a stock pump provides, which was enough for the 400 engine I had in my 83. Big solid lifter cam, Holley 800, etc.
I can't suggest strongly enough, get rid of all that ... stuff ... like Edelbrock pump, regulator, etc.; and put it back stock. Stock pump, good quality pressure line from pump to carb, hook up the return line. Probably will work FAR better. Certainly was more than adequate in mine.
Very sound advise! Sucks that I totally just bought the edelbrock pump brand new 2 days ago. Ive replaced all the lines and removed regulator. Car is running again. If I have any more issues I will do exactly what you said. I’m running a 383 stroker 750 double pumper pushing 450 hp at most.
now in the meantime what should I do with the return line? I have it vented currently. Should it be capped off totally?
thanks again for everything.
oh and I think I found my fuel flooding and rich problem. I’ll post another message after this one about it. I have too many things happening at once here.
Last edited by caddyescalade; 06-05-2024 at 11:29 PM.
There are not very many ways that fuel can get into the manifold with the engine off and the fuel pump not running. Since it is a mechanical pump, the FP running is not a potential issue. It's got to be some gravity draining the fuel bowls. If it was mine, I would change the gaskets on the bowls and metering blocks. I would fill the bowls manually (through the vent tubes or run the fuel pump to fill the bowls to the proper level in the site glass. Without draining the bowls, I would lift the carb and put a piece of cardboard under it (between the carb and manifold). Wait and look for evidence of leakage.
My guess is a bad gasket on the metering block.
Don
Williamsburg
Well I removed the carb and it looks like I have figured out my rich problem and my flooding problem. So I was filling bowls through the vent tubes with the carb off and once the floats get just over the edge of the site glass fuel starts pouring out of the Venturis both the primary and secondary. Seems like a simple fix to just lower the floats to be just at or below the sight glass like you would with removable plugs. The only kicker is the brawler manual says to have the floats adjusted so the fuel is sitting about 1/2 way up the site glass. So is there something wrong with it? I can’t see the manual for this specific carb being 100% wrong.
suggestions here other than the obvious to lower the needle and seat float levels to the bottom of the site glass and just move on?
If you have fuel leaking out of the carburetor when you have the floats adjusted to the middle of the site glass (as set forth in the instructions), you have some issue going on between the bowls and the body of the carb. If it were mine, I would not just lower the fuel level. I would take the bowls and metering blocks off and see what is causing it to leak at the prescribed fuel level in the bowls. Maybe the carb has a flaw.
in the meantime what should I do with the return line?
Doesn't too much matter as long as dirt doesn't get in it.
Yes your description does sound like some kind of misalignment between the instructions and the product. Not sure exactly how that would come to be; butt if the carb overflows, then no matter what else, the float level is too high. Clearly, filling it through the vents, sort of bypasses the needle & seat; but if it overflows before it gets to the level it would be at if controlled by the N&S, then there's a problem.
You could maybe get one of those cheeeeep electric pumps for lawn mowers and such, and use that to fill the carb via the normal inlets; raise the float level until it starts to overflow; then dump it out, lower the needle valve several turns, start the pump back up, and raise it slowly until it's maybe ¼" lower than the level it overflowed at. Should at least give you a starting-out point for further fine-tuning.
Yet again, addressed in the OP's other post about this, where installing a fuel pump with a return was recommended, since it keeps the fuel in the suction side of the system so much cooler.
This to me may have some significance.
What were the circumstances that it dies? Temps. Driving conditions?
I've dealt with the hot fuel issue and indeed a return line helped in that regard.
The wiped out cam lobe changed my direction and further cause and effect never happened.
As for the OP, a new cam would be hard pressed to give up the way my high mileage unit did. My problems only manifested themselves at about the 1/8 mile mark on a full drag strip pass. The engine full of former camshaft was the death blow for that one.
Doesn't too much matter as long as dirt doesn't get in it.
Yes your description does sound like some kind of misalignment between the instructions and the product. Not sure exactly how that would come to be; butt if the carb overflows, then no matter what else, the float level is too high. Clearly, filling it through the vents, sort of bypasses the needle & seat; but if it overflows before it gets to the level it would be at if controlled by the N&S, then there's a problem.
You could maybe get one of those cheeeeep electric pumps for lawn mowers and such, and use that to fill the carb via the normal inlets; raise the float level until it starts to overflow; then dump it out, lower the needle valve several turns, start the pump back up, and raise it slowly until it's maybe ¼" lower than the level it overflowed at. Should at least give you a starting-out point for further fine-tuning.
maybe this is normal as when I adjusted the needle and seat it would increase or decrease accordingly. Basically if I fill the bowl through the vent tube it will start to overflow when the level was higher than what was set for the float. So basically it’s acting like an over flow so it will not allow the fuel to be increased in the bowl past where the float level is set. I’m assuming this is likely normal so i most likely need to disregard this silly bench test.
This to me may have some significance.
What were the circumstances that it dies? Temps. Driving conditions?
I've dealt with the hot fuel issue and indeed a return line helped in that regard.
The wiped out cam lobe changed my direction and further cause and effect never happened.
As for the OP, a new cam would be hard pressed to give up the way my high mileage unit did. My problems only manifested themselves at about the 1/8 mile mark on a full drag strip pass. The engine full of former camshaft was the death blow for that one.
well I did something else that may have had a factor in this mess that I forgot about. I installed a small check valve between the fuel pump discharge and the line feeding the carb to prevent backflow. I have since removed that as maybe it was somehow causing excessive heat. Idk
It will be interesting to see if the removal of the check valve solves the flooding problem. I could imagine that you turn the engine off, the heat soak creates vapor in the fuel lline to the carburetor. That pressure cannot go back into the tank, so it pushes the fuel in the line into the bowl, past the needle valve. Overfills the bowl and you have flooding.
The bench test is still important. You need to see exactly where on the site glass that the fuel begins to leak into the body of the carb. I would still fill through the vent tube, but slowly, allowing the fuel level to equalize and watching the site glass. If leaking below halfway up the glass, you have an issue.
It will be interesting to see if the removal of the check valve solves the flooding problem. I could imagine that you turn the engine off, the heat soak creates vapor in the fuel lline to the carburetor. That pressure cannot go back into the tank, so it pushes the fuel in the line into the bowl, past the needle valve. Overfills the bowl and you have flooding.
The bench test is still important. You need to see exactly where on the site glass that the fuel begins to leak into the body of the carb. I would still fill through the vent tube, but slowly, allowing the fuel level to equalize and watching the site glass. If leaking below halfway up the glass, you have an issue.
Don
Williamsburg
the flooding issue was happening before the check valve installation.
the bench test I have confirmed that I cannot fill the bowl through the vents any higher than what the floats are set to. It will run out the Venturi everytime in the primary and secondary. I had a look at the design and have no idea how it this is happening. However when fuelling though the needle and seat when in the car, I can’t see this happening anyway as the needle and seat control the fuel flow. I’m confused
05-13-2024, 02:16 PM
