skirkland1980

iTrader: (2)

this is an addition to the sticky thread which can be confusing. if anyone needs holley tuning advise i will be glad to help.

skirkland1980

iTrader: (2)

ok. here is what i have to say about holley carburetors. a few tricks and things ive learned along the way that some of you may already know. if someone needs holley tuning advise i will link them to this thread. holleys have a bad rep for running rich. a few things that can cause a rich condition within the carb are high float level, blown/leaking/wrong powervalve, internally leaking metering block gasket, choke problem, clogged air bleeds. some things not carb related are, too cold spark plugs, retarded timing, clogged air filter, air flow restrictions within the engine such as wrong intake manifold gasket or mismatched intake ports. i think an exhaust blockage may cause a rich condition. the best advise i can give you is set up the carb back to stock specs, make sure its clean and the gaskets are new. if you still have a problem that would rule out the carb.
with the power valve (pv) rating, here is a rule of thumb i use. if i have a cam that has a low rpm range say idle-5500 or 1250-6000 or has a smooth idle i use a 65 power valve. if the cam has a lopey idle i start with about a 25 or 35. you can just remove the pv spring until you know what pv is correct. if your unsure why the power valve is so important here is why. the power valve is closed (allowing no fuel enrichment) by engine vacuum. at idle the vacuum is high, at WOT the vacuum drops. lets say you have a very lopey cam, at idle you may have 4" vacuum. if you have the standard 65 power valve it will not close causing a very rich idle. make sure the power valve is good (and correct vacuum rating) and the pv gasket is good. if the vacuum at idle is 10"+ use a 65pv, less than 10 divide your vacuum by 2. on secondaries i use a plug and 6-8 sizes bigger jet than the front (square bore carbs). make sure fuel pressure is 5-7.5psi and the fuel level is slightly below the sight plug with the engine running. some people say right at the bottom but it will be rich. also if you've had the metering block off of the main body more than a few times and did not replace the gasket you should replace them. I always run a flat file (just a few passes) over my main bodies to reduce the high spots. once you get the engine running, run the idle mixture screws all the way in, if the engine does not die you may consider drilling the throttle plates. one small hole in each primary.(without 4 corner idle 3/16" max) this will allow more control with the idle mixture screws. to set the idle mixture, attach a vacuum gauge, put the auto tranny in gear, adjust the mixture until max vacuum is achieved, then 1/2-1 turn out. the squirters will need to be set at 0 lash after the idle speed is set. if you change the idle speed you need to reset the lash to 0. bigger sqirters than a 37 need a 50cc pump. now, once your carb is perfect i can tell you what happened to me when i built my first race engine. i had a too small intake gasket causing a major restriction of air/fuel flow into the engine. it idled too rich and too lean under a load. no matter what i did to the carb i could not get it right. i pitty nascar engine tuners when they have to tune restrictor plate engines. i know there is a lot more to these carbs but this should sent you in the right direction.

JTNKTZ

iTrader: (10)

Alright I just rebuilt a 4777-2 Holley 650 DP carb not even 10 minutes ago. My first one

It went very smoothly just some questions.

The PV's that the rebuild kit (37-485) came with were 66(2 of them) and a 50.
My carburetor only has 1 PV on the primary side. It was 65. I rather not mess with it so I just kept the 65 in there but replaced the gasket. Is this going to be a problem?

I was told that my carb has only 2 corner idle mixture screws. The secondary side has holes for mixture screws but they stop screwing in about a 1/4 the way in. The primary side, both screws screw in basically all the way. Does this sound correct? Also what is a good base setting to run once I get the carb on?

What is a good fuel bowl level setting to start off with once I can tune it on the car?

Where is the idle speed screw and how do I tune it to it's specific needs?

What do you mean the lash on squirters?

How do I tune my carburetor regarding jets?

skirkland1980

iTrader: (2)

double pump carbs usually have 4 corner idle. i would check the number on the metering block to make sure it is correct for your carb. also check holley's website, they have all the stock specs for your carb. if someone had the carb before and didn't know what they were doing it could have mismatched parts on it. for jets i would start out with the stock sizes per holleys specs. once you get the car running you can see your engine's fuel needs. i would set the bowl at 1/2" to start. i would use the new pv that came in the kit if the cam makes good vacuum. 0 lash for the squirters means no space between the arms on the mechanical levers. start out about 2 whole turn on the idle mixture screws. set idle speed screw until you see about 1/16" of the transfer slot.

skirkland1980

iTrader: (2)

the primary metering block part number should be 134-150, sec pn is 34R6497AS

JTNKTZ

iTrader: (10)

Alright, well I got a 6497 sec metering block but the prim i can't read but it ends in 84?

The secondary squirter isn't 0 lash, so change that correct?

Where is the idle screw? and what you mean transfer slot?

Sorry I'm still learning.

Also there is what looks to be a vacuum port on the primary. Is this port for the vacuum reading for when I tune the carb? If not what is it for?

skirkland1980

iTrader: (2)

to help with some confusion. i'm going to make a video tonight on some of this stuff and post it on youtube to help out a little. i think i can help explain a little better that way. if you look at a holley main body, there are 4 barrels, at the bottom there is a hole. that is where is idle circuit is. above that is a slot, that is the transfer slot. that is where fuel is supplied between idle and wide open throttle.(WOT)

skirkland1980

iTrader: (2)

i just found some pics on google image search and labeled them. when the throttle plates are in idle position fuel is pulled, by engine vacuum, through the idle ports. at part throttle the transfer slots become exposed to engine vacuum and fuel is pulled in through the transfer slots. only at wide open throttle is fuel pulled through the venturies.

skirkland1980

iTrader: (2)

2 more

1988GTA500HP

Suscribed. This is 1 of the things I need to do. I have a 400ci with 750 DP. I know it needs tuning. I will def be watching.

one92rs

iTrader: (5)

you need to also mention that the main jets arent in the idle circuit at all. its its own circuit. set the idle mixture with an automatic in gear idling. manual idling in neutral. for a pv on an auto check the vacuum while idling in gear and cut it in half. should be darn close.off idle flat spots are more than likely a discharge nozzle and accelerator system. they also have cams for the accelerator pump as well.

skirkland1980

iTrader: (2)

the power enrichment circuit and the accelerator pump circuit are the only circuits that bypass the main jets. idle circuit, transfer, and main metering circuit are all fed by the main jets.

mos68x

I know that I'll be needing help, I just started today trying to tune my 670 avenger. After wasting a ton of fuel I have a 60 main jet in the primaries, but it still doesn't feel quite right. Very slight pause before power(stumbling?) applies when you press the pedal at speed. I'm still not sure what they mean by the surge while driving down the road, so I'll probably keep an eye on this thread as you write more. I put the 105 PV in that I bought and I still have a flat spot, but I stopped at that point since I only ordered one PV and also cause it started raining. Another problem that I have is that I cannot get the carb to drop in idle below 1000. I can back the idle screw all the way back so that it doesn't even touch the lever and it still won't drop. I can put pressure on it and it'll drop but not by itself. I've taken the throttle cable off to be sure that it wasn't causing the trouble and it still does it.

All I have to say is that I really wish that I hadn't sold my wideband O2 sensor, this tuning BS would be so much easier with that thing!


What is your youtube ID? I'll subscribe now and watch them soon as you post them.

skirkland1980

iTrader: (2)

whats the list number on the carb? with the idle see if the are holes in the throttle plates. if not the secondary idle screw must be in too far.

mos68x

Where do I find the secondary idle screw? List number? All I know is that the part number is 080670.

skirkland1980

iTrader: (2)

you should have 65 jets primary and 68 secondary. whats the engine vacuum idling in gear. your carb came stock with a 65 power valve. i listed the secondary idle screw in one of the pics.

one92rs

iTrader: (5)

the idle circuit well comes from the main jets. but the mixture that is gotten from the idle circuit is not the main jets.

mos68x

Engine vacuum at idle is between 19 and 20 in.

Are there marking on the PV's to show a difference between two different ones? When I looked at the one I removed and the one I put in I saw no difference between them other than the color of the springs.

Is the secondary idle screw recessed in a hole? That is a double pumper base plate, are they same between them and vacuum secondaries?

skirkland1980

iTrader: (2)

you should be fine with a 65 pv. yes it's recessed on the passenger side of the carb. it should have one. here is a pic a the pv ratings. you need to use the correct main jets. set the carb back to stock settings and go from there.

mos68x

I haven't done anything non-stock other than the main jets. Just got done doing the secondary screw and got the idle down finally. How do I know if I backed the secondary idle screw too far? After changing the sec idle screw the vacuum changed a little it seems to bog a little so I'm wondering if I turned it too far. I adjusted the sec idle screw with the choke cold so I was fumbling with the linkage trying to get it to stay in the closed position while doing it.

skirkland1980

iTrader: (2)

if the idle speed is good now you should be good there. why did you change to smaller main jets?

one92rs

iTrader: (5)

i had a 65 power valve on my stock engine. i kept getting a bogg till i went to a 95. half of 19 to 20 will be a 95 to 105 pv.

plasmeh

iTrader: (10)

I have a thread up but I thought I'd ask here too since I see some knowledge here:

My 4777-7 650 DP is not pumping any fuel through the secondary squirters. There is 0 fuel going through them, but the primaries are fine and the car runs fine. I checked the float level, and it is set so that if I bump the car pretty good, I get some fuel dribbling out. Also, if I tap the secondary fuel bowl while manually pumping the accelerator pump up and down, a slight misting of fuel comes out, but not a steady stream. Any idea what could be the issue?

skirkland1980

iTrader: (2)

do you have a check ball or rubber umbrella over the pump diaphragm? sounds like your problem is in there. if there was a blockage you would get a very very stiff pedal when you opened the secondaries. if the pump diaphragm was busted there would likely be a leak there. also make sure the spring over the diaphragm is not missing.

mos68x

It has been running too rich on this engine, ran better with the main jet change until i adjusted the sec idle screw.

skirkland1980

iTrader: (2)

a few things that can cause a rich condition within the carb are high float level, blown/leaking/wrong pv, internally leaking metering block gasket, choke problem, clogged air bleeds. some things not carb related are, too cold spark plugs, retarded timing, clogged air filter, air flow restrictions within the engine such as wrong intake manifold gasket or mismatched intake ports. i think an exhaust blockage may cause a rich condition. the best advise i can give you is set up the carb back to stock specs, make sure its clean and the gaskets are new. if you still have a problem that would rule out the carb.

plasmeh

iTrader: (10)

You were right on the money - the rubber diaphragm beneath the 30cc housing had come loose and was swishing around inside the housing. This caused there to be no pressure inside the housing and it was not pushing fuel. As soon as I replaced the rubber umbrella back to the right spot, the pressure built back up and it squirts like a champ now. I replaced it with a new one for now and will be rebuilding the carb soon. Great advice man, much appreciated.

skirkland1980

iTrader: (2)

glad i could help

GXR11

subscribed

JTNKTZ

iTrader: (10)

When I time it what should I be looking for? What degrees, idle mixture, vacuum etc.

skirkland1980

iTrader: (2)

a good thing to do when setting your timing is to use an advance timing light or put some timing tape on your balancer because it's best to set total timing. start out with light springs in the distributor. install your timing light, start the engine and get it warm, rev the engine while looking at where the timing is. try 3000rpm, then quick bursts just to make sure its all in. you shouldn't need more than 36 degrees. you'll have to drive the car to fine tune the distributor advance springs.

JTNKTZ

iTrader: (10)

Alright I am confused. What does an advanced timing light do? Timing tape? Advance springs?

Haha sorry :/

skirkland1980

iTrader: (2)

an advance timing light will advance the strobe with a dial. so if you wanted to set your timing at 36 degrees, turn the dial to 36 then the mark on the balancer would line up with 0. but they don't work with msd ignitions. http://www.summitracing.com/parts/SUM-G1059/ the timing tape is a tape that you put on your balancer that has degree increments on it http://www.summitracing.com/parts/SUM-162591/ and here is a photo of the inside of a distributor.

1988GTA500HP

Skirkland...I know I need a vacuum guage before I start my tuning. Should I order the Holley one or will my local parts store version be good enough? It's for a street car but I want to make sure I get a really good burn when it's all done. Thanks.

skirkland1980

iTrader: (2)

the parts store gauge will work. i saw the same vac gauge at autozone that snapon sells.

91zconvt

Alright, so I know next to nothing about carbs. Never had one before, but just bought a car with one. The person who I bought it from said it needs to be rejetted because of a cam swap (went from a bigger cam to more mild one). I don't know if it that's right or not, but it's what he said.

I'm going to try to give as much info on the motor as I know, and see if someone can confirm that is what it needs. It is a Holley 650 carb, don't know what model. I haven't even taken the filter off to look at it yet. Where would the model number be?

Motor is a 350 crate engine, casting# 10066036...350...........2 or 4...Target Master/Goodwrench crate motor, 2-piece rear seal, "Hecho en Mexico" Via Mortec.com

Heads are casting number# 3947041 Heads from a 69-70 Z28 64cc either 1.94 or 2.02 intake valve, don't know. Supposedly good heads.

Has an Edelbrock intake, don't know which one.

Hooker Headers, Flowmaster exhaust.

I do not know what cam is in it, and really have no idea how I would go about finding out short of removing it.

Anyway, it runs good. Only thing is, right about 2500-3000 RPMS, you give it gas an it falls on its face for a second then takes off. Only happens at that point, but happens consistently. I haven't gotten the chance to drive it much yet (registering it today) so I can't really comment anymore on it than that.

I know that this could probably be any number of things, but the previous owner seemed knowledgeable so for now, I'm going to assume he knew what he was talking about. Just looking for verification.

skirkland1980

iTrader: (2)

make sure the timing is no more than 36* total. check float level. get a vacuum reading on the engine at idle. run the idle mixture screws in and see if the engine dies (it should). the part number is on the choke tower. if everything checks ok i would disassemble and clean the carb, install a renew kit and set it back to new specs.

91zconvt

I think I'm in just a little over my head now...
I'm trying to learn, and well...It's a lot to take in at once. I've been looking at a lot of restoration threads right now, and I just don't understand how some of you guys can tear down a whole car to nothing and put it all back together. I mean, how did you learn all that?

Anyway, I digress...Pretty much everything you just said is foreign to me. I don't know how to check the timing; I know I need a timing light, but don't know how to use one/never had one.

Don't know what a float is or how to check the level

Don't know how to get a vacuum reading. Did take a hose off and def felt suction, don't know if that means anything.

Need to read a whole lot more, and get some tools. Always had access to my dad's tools but I just bought a house and have nothing now. Do have my own garage and a daily driver, so at least I can take stuff apart and not worry about needing to get it together right away.

Have driven the car more now. Took it out for a spirited drive. It actually hesitates more like 1500-2200 RPM's; Every gear, especially when you really push the throttle. Makes it quite annoying. Other than that it seems to run good. Does smell like gas, don't know if that's just normal for a carb, but can def. smell gas when idling. Oh, and it does seem 'slow' for what it should be pushing...maybe it's just me, or it could be the rear end. It came stock with 2.73's; don't know if they're still there and haven't gotten to checking yet.

skirkland1980

iTrader: (2)

sorry i missed your reply. you could send me the carb and i could check it for you. removing a carb only requires a few basic hand tools.

91zconvt

Sorry, missed your reply too

I'm a little weary of just sending off the carb to someone I don'tt really know, but I'll get over it...

That would be awesome if you'd be willing to do that. Like I said, I don't really know much about Carbs, or much at all for that matter, but what exactly would be involved in checking it? Does it need to be 'tuned' for a specific motor?

The car is a project car and is currently sitting in the garage while it undergoes a thorough interior restoration as can be seen in my thread on that subject. Anyway, what I was getting at, is that time isn't really an issue...yet

What would you like in return for doing this for me?

wrsjr

skirkland
Help me with this issue if possible. I have a 650 DP Quick Fuel Q Series. I have a lean bog around 1500-2000 rpm. Front & rear jets were 74 with a 5.5 PV. My vac at idle in gear (auto) is 10-11hg. The A/F ratio is good above 2000 rpm all the way through my rpm range, it only leans out around 1500. I went to a 6.5PV and changed the prim jets to 72 and it got way worse. What do you suggest?

As a side note, I previously had a 700dp Holley with a 6.5PV and 68/70 jets that ran fine.

skirkland1980

iTrader: (2)

is this on hard acceleration or all the time etc..? what is the fuel pressure and fuel level?

wrsjr

Hard accelleration it runs fine, only 1/2 to 3/4 throttle. The rear bowls have jet extensions. The fuel pressure is 6psi or so and fuel level at idle is about 1/3 of the way up the sight glass.

skirkland1980

iTrader: (2)

you will need to make the transfer circuit more rich. since quick fuel carbs work differently than holleys i am not able to tell you how to do that.

pancherj

The PV's were different from carb 1 to 2. I think that may be your problem. Try putting an 8.5 PV in and see if it helps. If it does, the 8.5 may be too close to your idle vacuum so you will have to step back to a 6.5 or 7.5.

wrsjr

They are the same as Holley Ultra HP's but yes different than older Holleys. It's a 2 circuit carb and not a 3 circuit

skirkland1980

iTrader: (2)

so your carb has no transfer circuit. then it must be a race only carb and would explain your problem.

wrsjr

It's a race carb but not much different from a regular Holley. The only differences are that it has adjustable idle & high speed air bleeds and adjustable emulsion jets. It it a regular 2 circuit carb like other 4150 Holleys. It has transfer slots on the secondaries. It's just like the picture in your post #8 above except my base plate & metering blocks are billet.

skirkland1980

iTrader: (2)

are the air bleeds replaceable? you could try smaller main air bleeds. that would richen idle and transfer but not the main power circuit.

onebad82z

iTrader: (7)

Although I agree the transfer circuit sounds lean in that case. A QF carb is the same thing as a Holley and all tuning theories apply. They work no differently.

2 circuit is most any 4150/60 style carb whereas a 3 circuit is a 4500.

Again I agree... selecting a PV is not hard depending on vacuum.

If you run the mixture screws all the way in and the car does not die DO NOT automatically drill the throttle plates. This means something is internally wrong and the carb is getting fuel from an internal leak. Wow. This drilling of throttle plates is a last step for having the throttle to far open usually due to insufficient timing and large cams therefore exposing too much transition slot in an effort to keep a decent idle.

I agree adjust mixture to highest vacuum in gear for an auto, but then only add 1/4 turn at most.

I have run bigger squirters than 37 with a 30cc pump. In this case the more important factor is to be sure and run a hollow screw. All but the biggest brown pump cam are fine with a 30cc pump.

"the power enrichment circuit and the accelerator pump circuit are the only circuits that bypass the main jets. idle circuit, transfer, and main metering circuit are all fed by the main jets"

Power enrichment via a PV is fed by the main jet. It does not bypass them.

99% of carb problems can be linked to insufficient and/or incorrect timing. If your car is street driven use a vacuum advance. Make sure your timing is 100% correct for your combination and then move to carb tuning.

DO NOT assume the car needs more jet before you have even ran it. Try it on the combo as it is built and see what the motor wants.

If you are swapping on a used carb I do agree it is best to rebuild it fresh with a Holley kit and set it up to holley spec for the list #. Always start with the carb in stock form.