InfernalVortex

iTrader: (4)

I can restart the engine when warm no problem, but then as soon as I hit my electric fuel pump switch, the car stalls out within a second or two, and dies.

I have to floor the pedal and crank for 5 seconds to get it to restart and when it finally does it spews tons of dark smoke and runs fine... until I hit the fuel pump switch again.

It's a Holley 4150DP with a stock TBI pump, going through a Mallory 4309 regulator set to 6 PSI.

I dont really see what it could be anymore. I used to think it was the fuel boiling in the carb feed line, putting boiling fuel into the carbuertor, and then the floats were sinking and then the bowls overflowing and spewing. But I now have the feed line set up so that it's not touching my valve covers or my upper rad hose, and it's STILL doing it.

I know a lot of guys who run setups nearly identical to mine, but I just cannot figure out what in the hell is causing this crap.

It's not the fuel in the carb itself causing the problems because it doesnt start until I hit the fuel pump switch...

Is it possibly my long tube headers boiling the fuel in the fuel lines near the trans tunnel? I thought that would just cause vapor lock though... and I thought vapor lock was just when you ran out of fuel, not when your carb floods over.

scooter500

iTrader: (1)

What does fuel pressure gauge do/read?

Ozz1967

iTrader: (4)

Ok...not exactly sure how you have yoru pump set up...why do you have to hit a "switch" for the pump ? Because it's originally carbed and you upt a TBI pump in it? As long as you've got it metered down to 5-6psi though your regulator, you should be money. Now, why do you hit the pump switch "after" you get it started? It should be running as soon as you key the ignition, that's how I've got mine set up.

vapor lock is caused when the fuel in the lines gets too hot and bubbles, creating air pockets which a mechanical pump cannot overcome because it's not strong enough and just "sucks air". With any kind of in-tank pump, that problem should be gone because it's pushing the fuel through the lines and has no air to suck.

InfernalVortex

iTrader: (4)

It was originally a TBI car. I have a factory electric pump. It's on a switch because that's how I wanted to set it up. Makes a lot of things easier actually and I'm glad i have it set up that way. And I turn on the pump after I start the car so that the pump isnt drawing from the battery at the same time the starter is and because the pump doesnt need to be on as the car is cranking. There's fuel in the bowls, why draw from the battery when I dont need to? If the car has been sitting for a while I'll go ahead and hit the pump switch and then fire up the car just to make sure there's fuel in the bowls. Doesnt really matter when I turn it on to be honest, but I've gotten so used to this hot start issue that I definitely make sure I dont turn it on until after the car is running, and that way if the engine starts to stall out I can kill the pump and then basically I can flick it on and off in short increments for 10-20 seconds and after that I can just leave it on since whatever the problem was, it disappears after the fuel gets run through the lines.

I even had an issue for a little while where my secondary bowl's float would keep getting stuck while driving - because I could kill the fuel pump when it overflowed and flooded the car, and turn it back on a few moments later as I used up the fuel in the primaries and run it until it started to flood again, I could actually keep it running and keep driving and get to a safe spot to pull over, or home if I wanted to. Was it really annoying? Sure, but I didnt have to pull over on the side of the road until I found a safe spot to do so.

gsmarcano

If you have an HEI distributor with the 4 prong ignition in the cap, have it checked. I had the warm restart problem too, bad ignition module.

Ozz1967

iTrader: (4)

If it overflowed, is your return line unobstructed? Not sure if that would cause any of the problems you've been having though. With the return regulator, unless your regulator isn't working right, you shouldnt' flood the carb.

InfernalVortex

iTrader: (4)

Well that's an interesting thought, but then, if the return line were obstructed, then wouldn't it overflow every time I hit the fuel pump switch? I can and have set the float level with the car off and just the fuel pump on, and it doesnt overflow in that situation. It also doesnt do it any time the car is cool. It's only when the car has been sitting for 15-90 minutes after getting to operating temp that it does this. It never overflows any other time. Im not even sure it's overflowing anymore. I used to think that's what it was but since I moved the feed line to where it's not physically touching any heat sources I dont see how the fuel in there could get so hot it would boil.

This is fuel-related, not spark-related. I've been able to narrow that down over the last couple of years fussing with it.

InfernalVortex

iTrader: (4)

Could it be the fuel lines being next to my long tube header collectors and absorbing too much heat from them? Is an inch or so of air enough for the fuel lines to get hot enough to boil fuel?

Ozz1967

iTrader: (4)

I don't think so, I've only got about 2-3" of room for mine. You could try wrapping your fuel lines in a heat shield. They sell this heat wrap for starters that you could try wrapping around your fuel lines. Still, with the fuel pump pushing" the fuel, that should get rid of any and all fuel boiling issues because the colder fuel is being pushed from the tank.

InfernalVortex

iTrader: (4)

Me and some friends were brainstorming and we've got a theory I want to bounce off of you guys.

If my fuel tank vent line is clogged, the pump/car itself will get warm as it operates. It would leave a vacuum in the tank after I parked the car, and it would be hot. Then as I first turn the pump back on an hour or whatever later, the vacuum and heat combined with the sudden draw would cause the tank pump to vapor lock.

Im going to leave the gas cap partially unscrewed the next time I take it out and let it sit for a while and see what happens. But does that theory make any sense to you guys?

Im not sure how that would affect the carb considering there's a regulator and floats between the venturis and the fuel pump... Seems like it wouldnt affect the carb itself at all, but my buddy has a carbureted car and he says his car does that from time to time.

Awesome-X

I had the same problem as you, and have tried all the things you have, as well as the ones you've suggested (gas cap being left off) and I never figured it out. I ended up solving my problem when I got rid of the car

InfernalVortex

iTrader: (4)

Yeah leaving off the gas cap didnt help a bit either. So right back to the drawing board on this one.

Did you have headers?

The only thing that seemed to help was running a crazy fuel line in front of the from radiator support near the hood latch and looping it back around from the passenger side and through the belt to the carb feed line. I dont know how thoroughly I tested it setup like that though. I may not have put it through the right conditions to aggravate the problem since it was just a casual weekend driver.



I may just buy some more fuel line and do that again and see what happens.

Awesome-X

LOL I did that, too!!! and I even ran my line in front of my radiator after that. And yes I did have headers too.

InfernalVortex

iTrader: (4)

You mind sharing any details about that setup? There's gotta be some common thread here. Did running it in front of the rad etc help you at all? It seemed to help me but I'm not sure. I wonder if the headers are so hot that the heat is wafting up to the fuel line. But people run their fuel lines next to headers everyday. It just doesn't make sense. Maybe its a fuel pump issue?

InfernalVortex

iTrader: (4)

An update. This is the first time I've been really daily driving the car in years, so I've been hellbent on finally getting down to the bottom of this issue.

So today me and my entourage have been speculating, brainstorming, and monitoring the issue as it develops.

So today after I got out of my Physics class (which lasts an hour and 15 minutes, so plenty of time for it to marinate) and it worked fine. No problem at all. Of course it was unusually cool this morning. Cloudy morning and we got our first whiff of fall.

So I mosey'd on over to the tag office and battled the line of ambiguous wait times to pay my tag tax, and went back out to the car 20 minutes later - worked fine.

Went back to my college to have dinner in the cafeteria, hung out with some friends, came out 45 minutes later, and I start the car with no trouble. I hit my fuel pump switch. And a moment later the car stalls out again. I immediately shut off the fuel pump, pop the hood, and pull off the air cleaner. I hit the switch while a buddy watches the fuel pressure and the carb. Fuel pressure stayed steady 5.5-6 psi (I think it's 6), but the carb spewed a 4-5 inch fountain of fuel out of the secondary bowl vent tube for a second, then it was done.

I do my usual pedal to the floor routine and it starts up several revolutions later. I go drop off my buddy, and hang out for a while. Come back out and we again watch it very close. I decided not to start the car, but to just hit the fuel pump switch and see what happened. Immediately another geyser of fuel spews out of the vent tubes, mostly out of the secondary bowl, but there was some out of the primaries too. Again the fuel pressure stayed steady while the carb acted a fool.

So given that the carburetor is spewing geysers of fuel out of the vent tubes upon presurrization of the fuel line, does that point to a float/needle valve issue, or does that still point to a problem with excess heat in the fuel lines? I'd lean towards it being a float issue except that it's DEFINITELY heat-related. Hotter ambient temps and hot restarts after enough time for whatever is failing to absorb heat is clearly what is causing this. Can float/needle issues be heat-dependent? Can a float level set too high in addition to the above cause this... except only when hot? Or does this sound like excess heat in the fuel line?

Awesome-X

It was a carbed 355 with 305 heads, it had a TBI pump in the rear that had been disabled and was only using the mechanical pump. It had an Edelbrock 1406 electric choke on it and some generic headers.

IROC315

iTrader: (9)

Keeping this thread alive. I am hoping you find an answer soon. I have had this issue on my tbi to carb truck and and one of my older camaros which I never did figure out.

InfernalVortex

iTrader: (4)

I have an idea that is cheap and may work. I've done a LOT of googling on it and the common thread is that everyone spends hundreds of dollars and never seems to figure it out.

I know the fuel in my carb isnt too hot because I can run the bowls bone dry and until then it runs fine. Its only when I turn on the fuel pump that it does this.

So I think what Im going to try to do, is find some electrical conduit plastic that fits neatly over my fuel line. You know the accordian sleeve stuff for routing wiring harnesses? Im gonna cut that to size around my entire fuel line from the regulator to the carb (including the carb feed lines) and then Im going to wrap some rubber hose around that. The rubber hose as a barrier, the conduit as an insulator, and then the braided fuel line we all know and love under that.

I dont know if it will work or not, but it's not THAT expensive, and it should be workable. I dont see how fuel could absorb much heat through all that, especially with the wire coinduit between the outer rubber hose and the inner fuel line. It would basically form as an air cushion between the two lines.

What say you guys?

A friend who is a whole lot more knowledgable about this stuff than I am thinks I just need to lower the floats a little, but given the amount of fuel that spews out of it, I dont think that could account for the volume. I see tons of people replacing needle/seat assemblies and seals and floats. Never fixes a damn thing.

Barring that I think my only recourse is to run a line from the vent tubes into a vented reservoir under the air cleaner. A vented canister full of fuel on top of the engine doesnt seem entirely safe, so I dont know how seriously I would pursue that, but it would work. It's a band-aid to a problem instead of a cure, but it would prevent the fuel from flooding into the engine as long as the fuel could be persuaded to follow the vent tube line instead of the other air bleeds in the carb. Beyond that, I'd have to find a way to seal the container to keep fuel in, and let air out.

I came across one guy on the googlenets, who ran a line from his fuel bowl to a T in his fuel pump return line. He used a nitrous solenoid that would activate when the ignition was off, and drain the bowls, and then when he restarted the car it would close and allow the bowls to refill. I dont think that's as effective as my piping the mess away from the carb via the vent idea, since I think it just gives the boiling fuel a place to sit without bubbling over. But just throwing that out there since it was one of the few things that actually worked.

InfernalVortex

iTrader: (4)

I decided to revisit some things and apparently my floats were set way off. They're now lowered to where they need to be and it seems like it has a moderate effect on the behavior of the carb. The bowls have more capacity in them to hold the boiling fuel spewing into them. It's not fixed, but it's better. THe amount of fuel that spewed out was a fraction of what it was. A HUGE improvement.

Now that hte amount of fuel that's making it out of the top of the bowl vents is reduced to a managable level... to fix it from here, I think I'm going to set up something like this:



The bowl vents would be connected, and the vents would be in line with the connecting tube, away from the barrels in the carb. That will just spit fuel into my air cleaner and even though its still boiling, it wont compromise my drivability.

Edit: I actually gave it a little more thought... and I dont think it would be necessary to do goofy things with where it's vented. I could just drill the top of the crossing line. The amount of fuel thats coming out now that the floats are set properly is probably not enough to completely fill BOTH vents AND the line across AND still be pressurized enough to get out of the holes drilled on the top of it. I may be wrong, I'll have to see. I may mock up a couple of them, one with holes drilled on top,a nd another with holes on the sides. But either way it will add capacity and redirect the boiling fuel away from an easy exit out the top of the bowl vents. It just might work even if the problem itself is still there.

InfernalVortex

iTrader: (4)

I have figured out what is actually happening.

The carburetor is NOT hot enough to boil fuel.

The fuel lines are NOT hot enough to boil fuel.

The carburetor soaks up engine heat, and makes the fuel in the bowls VERY hot... It's not hot enough to boil it.

The fuel in the lines, as soon as it enters the carb upon pressurization of the line, flash boils when it hits the hotter fuel in the carburetor. The extremely sudden increase in temperature in the newly introduced fuel causes a quick phase change and then boiling, and then, as the evaporated fuel leaves the vents, the heat is taken away enough for new fuel to be supplied with no drama. Thats why it only does it momentarily and then it's done. That also explains why fuel the bowls is fine until the new fuel hits it. It can handle a gradual increase in temperature, but once the much cooler fuel in the line hits the carburetor it flashes over until enough heat is removed for it to be a non-issue.

I have a feeling this happens a LOT more often than people realize it does, it just generally isnt severe enough to cause reliability issues.

I tried a makeshift solution connecting the two vents with a line across the carb and it worked beautifully. If I still had my cowl hood on the car and my 3 inch filter I could make one out of steel line and it would prevent the aforementioned flashover from getting fuel into the carburetor barrels. I lack the clearance under the hood to fit it in there, though.

But hopefully it will help someone figure out a solution in the future.

five7kid

iTrader: (14)

"Phase change" means going from one physical state to another, such as going from solid to liquid, or liquid to vapor.

How suddenly the temperature change occurs is irrelevant; it's the temperature (and pressure) the fuel is at that determines whether or not it changes phase. "Boiling" simply means that the fuel that is in contact with the container surface is hot enough to change from liquid to vapor, and the resulting gas bubbles rise.

By the way, the "boiling" is actually cooling the container, in this case the fuel bowl. Adding cooler fuel will cool the total mix even more, which would suppress boiling, not promote it.

But, hot fuel being pushed up to the carb is a different matter. You're using a TBI pump, which means the fuel in the line going by your exhaust is at a higher pressure than the carb fuel bowl. When it hits the fuel bowl (after passing by the restriction created by the float needle/seat), the pressure drops, lowering the boiling point of the gasoline. Bingo, boiling. The solution would be to shield or relocate the fuel line so that it isn't heated by the exhaust.

This is the same reason your cooling system is under pressure - to suppress boiling. And why you get a geyser if you remove the radiator cap when the engine is hot.

Connecting the vents like you did only helps prevent the Bernoulli effect of air flow going by the vents lowering the pressure in the bowl; assuming you have holes in your connecting contraption - if you simply plugged the vents, you just changed the pressure in the bowls. And that's not good.

InfernalVortex

iTrader: (4)

The fuel in the line by my headers is nowhere near the carburetor. Its a long way upstream actually nd if thhat was the culprit the problem wouldn't ONLY occur in thhe immediate 3 seconds after the fed line becomes pressurize. And there IS a definite phase change that occurs immediately preceding the geyswer of fuel that comes out the bowl vents. The vapors visibly change very dramatically before and during it happening. Its not just vapor in the bowl coming out as it fills... it LOOKS like the fuel is boiling.

Fuel has a rapid vaporization temperature before it boils. Its more likely that's what I'm seeing. But it definitely appears as if the whole system calms dowm as soon as temperatures equalize.

And of course my line is vented. Th effect of air rushing over thhe top of the vent tubes may or may not be tat significant. I don know yet.

InfernalVortex

iTrader: (4)

Okay you got me to thinking. I reevaluated. I think the fuel is reaching its vaporization temperature in feed line. As soon as it pressurizes the hot vapor is blowing past te needle/seat and pushing out fuel in the bowls in the process.

TreeFiddy

Bringing this back from the dead - somehow I have never noticed this thread, but just became aware of it with a link you made in a reply on another member's thread.

I had this exact problem for years too. Although mine was not so severe, I would get a predictable couple of seconds of surging about 15-20 seconds after a hot start, worse on hot days. Usually wouldn't quite kill the engine though, I'd just feather until it cleared then it would be fine. I never observed the geysers of fuel though; my floats were set correctly.

Like you, my online research turned up lots of guys who couldn't solve the problem, and finally found the bowl vent connect idea. Was about to try it when I inadvertently found another solution.

Our fuel lines to the carb are routed identically - from the original metal feed line (tbi in your case, tpi in mine) cut next to the lh strut tower, through a flexible hose lying across the motor, to the carb inlet on the rhs of the motor.

I inadvertently discovered that raising the flexible line up 2-3 inches fixed the problem. It had been hanging down into the hot exit airflow from the fans, heating the fuel and leading to the conditions as per your theorizing in posts 20+ above. This minute change in the routing had a major effect.

I note that you noticed a similar effect in post 12 above with the 'crazy fuel line'.

Connecting the bowl vents looks to be a bandaid, stopping the pressuring fuel that shoot out the vents from falling into the venturi.

spicyskater

hey u guys...well the only problem u have is that u using the tbi fuel pump on carborator...this is like to make u eat 5 bigmacks for lunch when u just need one...the needle is not ment to resist on this enormas for it pressure...and it ****s up ur carb levels...u need carb fuel pump

Ozz1967

iTrader: (4)

As long as there is a regulator to bring the psi down to 5.5psi the type of fuel pump doesn't matter.

InfernalVortex

iTrader: (4)

Most of us are using adjustable fuel pressure regulators to bring the pressure down to a reasonable range. I have a Mallory 4309 and it's apparently the standard regulator for this type of deal. It's a quality 3-port, return style regulator. Carb is only seeing 6 psi like it owuld with a mechanical pump. I've dropped it down to 4 and up to 7 and never made a difference.

Ozz1967

iTrader: (4)

spicyskater

you guys u think u got it all figured out...its been about 12 years now that i repair cars and invators like u are every day ,what makes u think that u r smarter than the manifacturer????!!!!....here is a fact if u put carburator fuel pump problem solved u done u good to go!!!! u guys think u can cheat the devil u by regulator u put cabels around the car for the elctric fuel pump u put swiches where they don belong...and all that so u dont put carb fuel pump...and yes i am grown enouth to know what fuel pressure regolator du...unles u have fuel injected engine u dont need that huge amount of fuel circling around the hoses.....

Ozz1967

iTrader: (4)

Whatever dude. You need to learn how to spell and use proper grammar while you define just what a "Carburetor fuel pump" is, because you haven't.

Facts speak for facts. Carbs don't care about the way the fuel is delivered, they only care about how much pressure there is. Once you set the the fuel pressure,that's all that is going through the lines because that's all the regulator is allowing to go through.

When my motor blew, I swapped in a new one that wasn't drilled for a mechanical pump. I kept my original induction which included a Quadrajet carb. So I wired in an electric in-tank 255lph pump using my fuse box and a relay kit and there are no switches or the like. It comes on with my ignition, just like from the factory! Imagine that!? I then used a regulator to bring the pressure down to 5.5psi, oh wait, just like my original mechanical fuel pump! In more than a year now, I've had no issues. Several more people on here have gone even longer. So, while I definitely don't have "Everything figured out", I did figure this out with a little help from my friends. Thank you TGO.

spicyskater

anyway i am not here to argue whit anyone about my spelling or about my skills i am here to give advice to the person who is fludin his carborator whit the tbi fuel pump cose for him the regulator probably dasent work like it works for some outhers or something is not conected the right way...anyway there is low pressure elektric carb fuel pump u can use if u dont have the engine drilled for the regular one...and that will solve ur fluding

InfernalVortex

iTrader: (4)

The regulator works fine. Thanks for your concern.

naf

iTrader: (7)

A few thoughts and maybe some clarification (did you get it solved?), anyway:

Gasoline is a mix of different compounds, each with a different boiling point (between 100F and 400F?). Some part of this mixture may have boiled out of the carb before the introduction of new fuel into the bowls.

Gasoline in the lines will be subjected to a higher pressure than atmospheric. The boiling point for a fluid at 5.5 psig, directly in front of the needle/seat, is going to be higher than the boiling point for the same fluid at 0 psig. Fuel that would not boil in the lines 'may' boil once it's exposed to atmospheric pressure in the bowl.

InfernalVortex

iTrader: (4)

For whatever reason, my lines dont stay pressurized after the car is turned off. So the fuel that's in my feed lines isnt at 5 psi just before I fire it back up. That is an interesting angle though... I will have to let it marinate for a few and see the implications.