Hard to start when warm/hot?

1968 with 302 and auto trans

My car starts-up right away when cold. When it’s warm/hot, it almost always requires I put the pedal to the floor and crank for about 5-7 seconds and it finally starts. This works every time but can’t be good for the starter. I’ve tried pumping the pedal, one-pump before starting, just about every combination I can think of. The mechanic has replaced the points and condenser. It made no difference. Often I have to give it some gas once it starts to keep it going but once it get’s going it idles fine.

Does anyone else have secrets to starting? Is this common?

How is your fuel line routed to the carb? Is it a long distance that travels over lots of hot engine parts?

Could be the fuel lines are getting to hot and is causing the fuel in the fuel lines to vapor. I know on my Cougar on hot days with a hot motor it always took an extra pump or two of the gas pedal and a few more seconds to get the motor restarted after turning it off for a couple minutes, especially at gas stations as turning the car off hot and filling up and restarting a short while later and this sounds like your symptoms.

What kind of gasoline do you put in it? Is it fresh and good quality?

Vapor lock, gasoline is boiling in the carburetor. My Cougar did the same thing, went to a cooler thermostat and finally blocked the manifold heat to eliminate the problem.

Thanks. How did you block the manifold heat?

Usually HOT start issues are a combination of problems. The main problem is trapped heat under the hood. When you stop and shut off the car for short periods, the motor builds and releases heat in the engine compartment. This creates temps above normal,…just look at your temp gauge before you shut your motor off. The gauge will read at about 1/2, then when you go to restart the gauge will be closer to 3/4. There are several things that can be done to displace engine heat and the effects it has on the fuel/motor. Make sure the heat riser flap from the stock air cleaner remains closed off during summer driving. Insulate fuel lines from engine heat. Advance your timing a little,…this will take some of the compression load off of the cylinders,…but not too much or you will loose top end performance. Composite carb. spacers,…just thick enough to isolate transfer heat from the intake manifold to the carb. Fresh air induction, keep intake air and the carb. cooler,…lessen fuel boil potential. Increase air flow over the motor while driving, air dam diverters and fresh air sources through the core support can keep overall engine temps down. Lower temp t-stats during summer driving. One or a combination of these solutions should solve or lessen hot start problems,…as long as the motor and its components are in good operating condition.

A thin piece of stainless steel to go in the intake gasket at the heat crossover.

This may be a vacuum leak. more on that in a minute… I am assuming this is a stock carb and manifold? We need a lot more info to diagnose this. Can you tell us exactly how the car is equipped? bone stock, carb never been touched etc?

Check this: pull the air cleaner. Use your hand to rapidly crank the throttle while looking down into the carb. You should see two streams of gas going into the carb. If you do not, then the carb may be either boiling the gas out of the bowl, or it is most probable leaking down into the intake manifold. If the gas is leaking into the manifold then you have an odd combination. At start the engine is flooded. You have to hold you foot t the floor to clear the excess gas already puddled in the manifold. Then when it starts it is lean because the bowl was empty. It takes a few seconds for the fuel pump to recover and fill that back up.

If you did see streams of gas that is is good thing. Cougars have tons of vacuum accessories that can add up to a major vacuum leak. A vacuum leak is letting air into the engine that is not passing through the carb, This causes a weak lean idle. You can try to offset this by adjusting the idle air screws, but it really is not the same as getting more air flow through the carb itself. So you might try disconnecting and blocking off all of the vacuum lines and then seeing how it starts. Then connect them back one at a time and when the idle drops or gets a little rough, you have found a problem.

I never knew what those plates were for,…and have thrown them away when included in intake gasket kits. Education.

I had 2 cars (both 70 351C) doing the same thing… gas boiling when off and hot. 1/2" phenolic spacer fixed it right away.