fuel boiling after shut-off

I am having trouble with the fuel boiling after I shut down. Any advise as to how to solve this problem. It seems that it boils in float bowl and then squirts into intake flooding it. The engine is 318. It makes for a rough start after sitting a couple min 5 to 10. Its fine if i dont wait to long.

you got to get that fuel cooled off,,,,,,,,,,is the fuel line close to anything hot,,,,,,,,do you have some sort of heatsink/isolator under the carburetor  to keep the intake heat from getting to it,,,,,,see if leaving the gas cap off relieves the pressure going into the carb,,,,,,,,do you have an electric fan with a timer on it mounted under the floor to cool off the radiator, carb,,, doghouse,,, you and blow those fumes out?????

Donivan well it seems I had a number of issues when I got into it. I checked the timing witch I hadnt yet sence I got it it was at 0 at idle I advanced it to 12 man what a difference Ive been driving around a slug the last month or so. It seems it might have solved the problem but not sure I want to try and tune it a bit better. Thanks for your help I do need a fan in there as you say coming soon. Any tips on timing whould be great also it seems when I try and get total timing I cant see the line?

,,,,,so you want to talk about timing,,,,,,,,the points fire the coil,,,,,,the coil sends spark to the rotor in the distributor,,,,,the rotor, which is watching where the piston is,, sends that spark up to each wire going to the spark plugs,,,,,,,so you twist the distributor to move the spark plug wires in the cap to adjust WHEN,,,,you want that spark go to the spark plug,,,,,,,and its all in Degrees,,,,and you want the spark to start BEFORE the piston gets to the top,,,,and the faster the engine goes you need to start the spark to catch that piston in time,,,,,,I would say your timing COULD be 10 degrees before top dead center,,,,,,,your centrifugal advance weights add another 10,,,,,,your vacuum advance adds another 10,,,,,,so 30 degrees COULD be your specs,,,,,,,you need a timing light with the variable advance checker to see what you got,,,,,,,,you put the dial on 0,,,,,,remove the vacuum hose from the distributor,,,,,,,adjust the marks to 10,,,,,,speed the engine up, marks should run away,,,,turn the dial until mark comes back to 10,,,,,,read the dial, that is your centrifugal advance,,,,put the vacuum line back on, race the engine, turn the dial back down to your mark, read the dial, that is your total centrifugal and vacuum advance,,,,,so you can tell if each one of those advances are doing its job,,,,,,,,but most important is make sure the points are good and adjusted,,,,,,the points are the root of all evil things that happen to vans,    now if you did all this and you still cant find the line, then you need a better timing light or move the clip to the coil wire instead of #1 to check the timing......

Hello, check the bowl vent of the carburetor. I had this problem with a Holley 1920 and a Carter 4300S.

Alfredo M.

I think the timing was my biggest issue. I need an advanced timing light next to dial it in like Donivan was saying . I might still be boiling fuel but it starts right up now and lots of power. I of coarse want all the power I can get..... Thank for the advise I soak it up like a sponge so you all help. THANK YOU....

Donivan I am tring to dial the van in today and I have the right light.I set the points .018 and with vac. disconnected set timing to 10 then I run higher rpm 2000 or so 20 degrees then race to 4000 rpm or so 30 degrees when im at 30 degrees I dial light all the way till 60 and only moves mark to 20 degrees Also when I hook vacuum up no change in rpm or light

you want about 36 full advance at 3000+, no more. Put a vacuum line on the distributor advance and suck on it, it should hold pressure on your tongue, if not the diafram is shot in the vacuum advance, also make sure there is constant vacuum on the hose from the carb/intake

,,,,you disconnect the vacuum line,,,,,,let the engine idle,,,,see what the timing mark says with that timing light set at 0,,,,,,,,speed up the engine,,,,,timing mark disappears,,,,,turn dial to bring it back to what you seen at idle,,,,,,that is the CENTRIFUGAL ADVANCE,,run the same test now with the vacuum line connected,,,,,,,,you should  get a bigger number than what you got with that centrifugal test,,,,if its the same number,  VACUUM ADVANCE aint adding its part to the engine,,,,,,,we want to see if both units in the distributor are at least working,,,,,,,then you can test if they are working correct by matching the amount of advance to the engine RPM,,,,,,,,,,and make sure that vacuum line has no vacuum coming out of it at idle and you feel some suction when you speed up the engine,,,,,,

Well Donivan vacuum advance definitly not working. And I got one on order but going to be a couple days. I have good vacuum, and no vacuum at idle. So I gots the feelin its gonna do wheelies after we fix it..... Boy it runs good now I can't wait........So now at idle I am setting all by ear and this is what I did I turned idle jets in till almost stalled then backed out about 3/8 to 1/2 turn.It seems to be right there but I just want to here how you would do it.

There are 2 types of vacuum, ported, which is the air flowing down into the carburetor,,, AS,,,you let the air in when you step on the gas pedal and that is used for the vacuum advance,,,,,no vacuum at idle,,,,and the other vacuum is manifold vacuum,,,,,,,full vacuum at idle,,,,,,kind of hard to find on our Earlys,,,,,there would be a fitting into the intake manifold,,,,,now that vacuum represents fuel mixture,,,you would adjust the mixture screw to get the highest vacuum reading out of that port,,,,,,but our common way is to turn the mixture screw in until the RPM slows and keep backing it out until the RPMS quit increasing,,,,

Donivan great advice again thank you !!! I got my vacuum to 17 and like you said that was the highest idle..And then I turned out the adjuster screw that was barried all the way in on the linkage. Set that idle to where it sounded smooth. I'm still waiting on the vacuum advance unit ordered it and just got word not till 13th... man long ways away.....

Van Crazy,
Fuel boiling can be caused by a stuck heat riser valve in the exhaust manifold. That valve is meant to divert heat up into intake manifold bottom to heat the passage for a choke that is heat activated. If your carburetor has an electric choke, your engine doesn't need this heat riser valve, so check and see if your engine has one. On the 318 and 273 V8s, it's on the right side exhaust manifold. It has a return spring and counter weight but it can easily get stuck. Check the freedom of movement of that butterfly valve by manually moving the shaft connected to the counter weight. Put some penetrating fluid on the shaft to free it up. Keep working it until it returns freely. An old manifold can get quite clogged up with carbon and soot, so you might not be able to free the valve without removing the exhaust manifold and even removing the valve and cleaning out the interior of the manifold.

One thing that I did was to install a spacer under the carb to help isolate it from the intake manifold heat. Used a plastic type, or compressed wood type. Do not use an aluminum spacer. I also wrapped the fuel line from the pump to the carb, I used some insulating material, then wrapped that with aluminum foil, then zip tied it together.
Anything you can do to keep the carb and fuel cooler cant hurt.

reroute your fuel lines up the firewall, iirc they run along the passenger side frame rail by the exhaust manifold (my 65 did anyway). Add a carb spacer as well.

Van crazy wrote:I am having trouble with the fuel boiling after I shut down. Any advise as to how to solve this problem. It seems that it boils in float bowl and then squirts into intake flooding it. The engine is 318. It makes for a rough start after sitting a couple min 5 to 10. Its fine if i dont wait to long.

I had the same problem on a 350 chevy last summer. The intake manifold would get so hot, and the heat would soak into the carb after I shut the engine off, causing the fuel in the carb to boil. It would then condense and cause a flooded condition.

I solved the problem by adding a one-inch phenolic plastic spacer between the carb and the intake. The plastic spacer created a heat barrier between the hot engine and the carb. I have heard of guys using composite material spacers, or even making one out of hardwood.

so iam have the same problem can you show me how too get or make the plastic spacer?? KooK

Rick's 66 Chevy Van wrote:so iam have the same problem can you show me how too get or make the plastic spacer?? KooK

Summit Racing has them. Or You can make them out of wood. Look on google for wood carb spacers, they work !

I got one through napa or one of the local stores (plastic style) - I had to modify it a little, but it works...

It's actually layers of fabric or paper soaked in resin forming a laminate. Phenolic spacers