Hot soak fuel condition,edelbrock

[LSR]

Hello,everyone,this is my first post here,so here we go. 1969 chev pu,350 cid,th400. Truck has an edelbrock carb,and when let sit after a long run,temp naturally rises and starts to boil the fuel out of boosters,then a rich start condition. I have tried all the fixes I can think of such as,Thickest insolater gasket ,lowering the floats,epoxieing the 4 plugs in base plate,pressure regulator set and checked 4lbs.fuel line isolated from heat,being desperate I went old time and placed wooden clothes pins on fuel line "Old time ford trick",still have issue. Inoticed the fuller the gas tank the worse it is.Tank is in stock location behind seat. Maybe one of you have heard that the older trucks with tank in cab have a tendency to push fuel from gravity,being tank is almost as high as carb. Has anyone have any insight to this,Im thinking theres a Q-jet in my future.

[celcius232]

You say you uses the thickest gasket, but have you tried a phenolic or other insulating carb spacer? I thought Edelbrock carbs were less prone to this issue than Holleys. I think fuel blends these days tend to be much more prone to the issue you describe.

[LockDoc]

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As mentioned above try the phenolic spacer (3/4"). I think some manifolds have exhaust gasses routed through the manifold in the carb area and I think you can get plugs for the holes. I am going from memory on this so you may want to ask over in the "Engine & Drivetrain" forum to make sure my memory hasn't failed me....

Oh, and to the board.
LockDoc

[clemsonteg]

Originally Posted by LockDoc

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As mentioned above try the phenolic spacer (3/4"). I think some manifolds have exhaust gasses routed through the manifold in the carb area and I think you can get plugs for the holes. I am going from memory on this so you may want to ask over in the "Engine & Drivetrain" forum to make sure my memory hasn't failed me....

Oh, and to the board.
LockDoc

I think you are right about the exhaust. I know my uninstalled edelbrock intake has a crossover for exhaust which is directly under the carb. An old hot rod trick (and something which was done to my intake before I bought it) is to close up 1 side of the crossover with epoxy and drill a hole to allow some air to pass through. I think it keeps the intake warm enough for street driven vehicles, but not too warm as boil fuel from the bowls.

[cdowns]

check your gas cap for pressure buildup due to poor venting of the tank

[clemsonteg]

Originally Posted by cdowns

check your gas cap for pressure buildup due to poor venting of the tank

Would pressure build up cause an issue or just vacuum from lack of venting?

[Swar]

Excessive pressure or vacuum in the fuel tank is never a good thing. The tank should be properly vented. On a stock C10 gas tank (in the cab), there's supposed to be a vent line that comes off the tank and travels up the roof inside behind the passenger's seat and returns back down through the floor.

My truck gets heat soak/vapor lock in hot weather, but all I do is hold the gas pedal to the floor. It blows some smoke out but starts every time.

[LockDoc]

Originally Posted by Swar

Excessive pressure or vacuum in the fuel tank is never a good thing. The tank should be properly vented. On a stock C10 gas tank (in the cab), there's supposed to be a vent line that comes off the tank and travels up the roof inside behind the passenger's seat and returns back down through the floor.

My truck gets heat soak/vapor lock in hot weather, but all I do is hold the gas pedal to the floor. It blows some smoke out but starts every time.

If I remember correctly the '71's and '72's are the only trucks that had the vent line that went up between the cab walls behind the passenger seat, because they had the emissions stuff and a fuel return line. I know the '69 doesn't have it.

LockDoc

[Swar]

That's right, before that it was a vented cap, right? I think the caps weren't as good though, they would leak.

[LSR]

The reason I brought up the fuel tank is over the years Ive owned a few chevy trucks, three of them all different carbs and engines these three including 69 Im working on had this problem,1967 GMC V-6,51 chevy mild 235. Upon talking to an old timer that was in charge of the state of Mass. highway dept. trucks in the late 50s early 60s his fix for this was a solenoid type valve that shut off fuel when parked.???? I dont know. FWIW the co. I buy carb. rebuild kits informed me because of the fuel,and how much ethanol Im getting in my area I may not cure this. My concern with a thicker insulator, is signal to boosters. Thank everyone for your responses.

[Jrainman]

Something to look in to is are you running the correct size fuel line 3/8 = V8 5/16 = 6cyl and I agree proper venting of the fuel tank is something to look into because temp and pressure go hand in hand raise pressure temp goes up . (change boiling points)

have you tried switching grades of fuel 93 ,89,87
also after your long ride have you tried to take the fuel cap off and leave it off .
the other thing is 4lbs sound a little low I could be wrong but I thought both holley and endlebrock recommend 6-7 lbs 6 being best

[mike16]

mostly its the karap fuel your using

also maybe your engine is running hot

[BLT gmc]

I have lots of experience with gas tank behind the seat. One filled the oil pan full. Almost all the old grain trucks use a selector valve to prevent this. Have you confirmed the fuel bowls are emptying? The reason I ask is if the tank is full and liquids expand, fuel could go past a faulty needle/seat an cause lots of problems. Keep us posted. Good luck. Bruce
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[engineer_gregh]

I'm running the 3/4" phenolic spacer and a new in cab gas tank, neither really helped. I installed the Edelbrock fuel pump and it improved a lot. Still happens sometimes but much improved. I also run Sta-Bil marine ethanol treatment with every tank of gas.

[LSR]

BLT that valve you speak of is their any info you know of,so I can track this down. 4lbs. is the minumum edelbrock now recommends to help problem.Im sure its leaking past the boosters,I can take air filter off after a long run,and watch the boosters sweat. I also added some startron fuel additive,if anything the mtr. gets up to operating temp. quicker with the additive.Everything Ive done gets me closer to fixing the problem. Stupid me I was thinking open phenolic spacer,when I walked away from computer yesterday it dawned on me use a 4 hole spacer,that will not hurt signal,may even increase it. Ichecked for vapor lock ,not an issue. FRom what Ive read??? chevy big blocks and small blocks seem to be affected more than others with the edelbrock carb.This is a new engine ,so I dont want to be washing the cyls. although I use marvel mystery oil every fill up.

[mike16]

run some av gas thru it. if the problem goes away then its the quality of the fuel you are using. shop around for higher octan. Some are 91 some are 93. THe alcohol content is also part of the problem.

to fix it, you got to stick with higher octane fuels and chip away at any hi heat conditions under the hood.

also in general aviation industry they have fire sleaves that slide over fuel line to protect them from heat of fire. Not cheap at about 4-7 dollars a foot, comes in orange or black. ugly but effective.

try Aircraft Spruce and speacialty company.

all those other fix's ought not to be needed. Never heard of clothes pins fix.

I might consider rebuilding the carb using a kit compatible with alcohol based fuels. lots of kits out there that are not.

[BLT gmc]

LSR,
There may be other valves out there, but this is the one I have the most experience with. Do not ask about the F***. www.tomsbroncoparts.com. Manual fuel selector valve and selector tank indicator plate. $$$ but good stuff. Bruce
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[bowtie72]

I am fighting the same problem with one of my trucks. My 72 402cid 400thm. It has a q-jet. It has been sitting for a few years. When I was getting it back on the road the fuel pump was leaking. I replaced the pump with a cheap Oriellys pump. Thats when my problem started. I have owned the truck for about 20 years. It has never done this before. I have rebuilt the carb and checked float settings etc no help. My son drove it to school and it done it to him. I could pour water over the carb and it would boil it off.
So I know the fuel is boiling in the carb and building pressure that the fuel pump wont push thru. I am going to change the fuel pump to a better quality pump, and I have a phanolic spacer to try if that doesn't work. I think it is the cheap pump not pushing thru the vapors in the carb. I will let you know what happens.

[mike16]

I have had fuel pump problems for over two years because of cheap chicom pumps. 4 pumps later I spent almost double from 19 bucks to 38 bucks on my last pump it has worked flawlessly for over 4 years. NAPA

[leftybass209]

I read through some of this, but there will be some redundant info in what I list I'm sure:

Did you use a heat gun to check the temp of the carb at temp? I used an isolator gasket and could hold my fingers on parts of the carb after install; before it was too hot to touch.

Verify your fuel tank is venting properly, a new caps vent system has too much pressure on the springs to effectively vent the tank, many times it must be disassembled and have the springs cut to better vent pressure.

Ensure your engine temp is accurate, the hotter it is, the hotter everything else is.

New fuel sucks, but it's not so bad that with all these fixes it would still be an issue. My truck has idled in 109 degree Temps shut off, turned on, and ran hard without any issues with CA low or mid grade fuel.

Some of the "fixes" to your carb may be aiding an issue.

If all else fails, find a Quadrajet or Holley and see if that helps.