Fuel System: Hard starting in hot weather

[SuperHawk]

My freshly rebuilt 1964 259 V8 has an Edelbrock 1403 carb with a half inch aluminum spacer and several carb mounting gaskets both over and under the spacer. My hope was to insulate the carb from heat, thus attempting to avoid vapor lock and fuel boiling out of the Edelbrock. Well, I've not experienced vapor lock with it yet while driving, but I've got to crank it way, way too much to re-start after driving on hot days.

1) Should I have used a phenolic spacer rather than the aluminum?

2) Any other ideas ??? (Car does seem to run OK after it gets running, but, it seems a bit gutless).

Thank you,
Larry

[Kurt]

I had the same problem exactly. the thing that finally cured it was intake manifold gaskets that cut off the heat from the exhaust cross over.

[JohnM15]

There are a lot of things you can do to help but eventually the heat from the engine will heat the carb given enough time during a heat soak. Heat soak is when the engine is up to operating temperature and the engine is shut off. With the hood closed and no air circulation (engine fan not rotating) the carb will eventually overheat. Actually this includes everything in the engine compartment will stabilize to some high temperature depending on the outside ambient temperature. I have the same problem. I am thinking of a fan to blow directly onto the carb that is fed from a duct to outside air. When the ignition switch is shut off the fan would run for some time as to cool the carb suitably. This will help but will work marginally when the ambient temperature is above 100 F. The reality is that today's fuels suck and there is no additive to cure them...

[Chucks Stude]

An electric fuel pump has greatly helped the problem as far as I am concerned. I just have to remember to let it run for a few seconds to build up pressure when it is hot.

[PackardV8]

X2 - an electric fuel pump and blocking off the heat riser will cure 99% of hot starting problems. Adding a fuel return line to the tank usually fixes the remaining 1%.

Usual disclaimer, the above assumes the engine is in good mechanical condition, carburetor float level correctly set and ignition with new parts and correctly adjusted.

jack vines

[JohnM15]

An electric fuel pump can help with vapor lock in the system up to the carb, especially if you put in a return line to the fuel tank but it won't help (much) if the carb is boiling over. I say "much" because an electric fuel pump will deliver cooler fuel to the carb but with a heat soak and high outside air temperatures, the carb can boil.

In a modern carb the fuel bowl vent is open all the time (no valve) into the carb air intake above the venturi (the tube sticking up into the air cleaner). This is done to compensate for the a gradually restricting air cleaner over time as the paper element plugs up. In a oil bath air cleaner this is not a problem. When the carb bowl boils, the fuel then enters the venturi and floods the carb. This is why it is sometimes hard to start. In the older carbs, the bowl vent has a valve on the top to vent the bowl to atmosphere when the throttle is at idle. With this type of carb, when the bowl boils, you'll see fuel coating the outside of the carb but does not affect starting significantly. Here is a list of things to do to help:

1. Insulating carb spacer
2. Blocking off intake heating mechanism
3. Carb thermal shield
4. Fuel pump thermal shield
5. Fuel line thermal shield
6. Electric fuel pump
7. Fuel return line (for both electric & mechanical)
8. Carb fan fed from outside air

And finally, my favorite:

9. Fuel of the 40's/50's/60's formulation

All of these will help, some help vapor lock, some carb boil, some both. After reading some of the research done on fuels, I have come to the conclusion that today's fuels are designed for pressurized systems that are essentially immune to fuel boiling. They are composed of several additives that boil at different temperatures, some as low as 100 F. The result is that our non-pressurized systems (carbureted) suffer...

[FlatheadGeo]

I had that same problem with a 1969 Montego. Went with a phenolic spacer and problem was solved.

[prez55]

Have solved the same problem on 2 Studes with edelbrocks with the phenolic spacers. It was what edelbrocks tech line said to do.

[JoeHall]

I have tried most, if not all the above. Wiring the heat riser open helps a little; blocking it off at the manifold helps a lot, but the trade off is it takes forever to warm up when the weather cools, in winter it will NOT worm up. Running a fuel return line enables one to drive away sooner; without it, its usually necessary to sit for 2-4 minutes at real fast idle for the vapors to clear the line; it does NOT help it to start better though. Electric fuel pump should be standard on every Stude. Aluminum and phenolic spacers both perform about the same, and as someone else mentioned, it is not so much the heat transference from engine to carb as it is from the entire engine compartment temp when shut off and heat continues to rise due to zero circulation. Venting the fuel bowl to the outside did not help on the AFB I tried it on.
If anyone ever figures out a way to eliminate the hot start problem they'd deserve an award!
Luckily, the Stude starters will last a long time, even cranking & cranking & cranking on hot starts.