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Won’t start when hot...


Frijolito
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So here is the problem I’m have. Car starts fine when cold/cool. The problem is when it gets warm/hot it won’t start. The car runs great not over heating at all the temp gage is normal meaning 180° thermostat opens cools to 160°. Fuel is at the carb when I try to start it warm so no vapor lock. It turns over strong for a 6v. 

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If your engine is cranking at the same speed hot as it does when cold, you may be experiencing percolation.  The warm fuel in the carb float bowl boils a little, causing fuel to be forced out the metering jets where it pools in the intake manifold at the base of the carb, flooding the engine with gas.  Too rich a mixture won't ignite.   When you start your warm engine, try slowly flooring the gas pedal (so as not to cause the accelerator pump to squirt even more raw gas into the mix) while you are cranking your engine.  Having the throttle wide open helps clear out the unburned gas that has collected, and lean out the overly rich mixture so the car can start.  

 

If the car cranks over more slowly when it's hot, it could be  a couple things.  Check your electrical connections to make sure they are clean and tight.  Make sure your battery cables are the correct gauge.  Also check your starter.  I found that when my starter got hot from the warmed engine, the shaft would bind in the bushings.    I reamed out the bushings a little to get more clearance, and the starter now spins freely hot or cold.

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1 hour ago, Pete O said:

If your engine is cranking at the same speed hot as it does when cold, you may be experiencing percolation.  The warm fuel in the carb float bowl boils a little, causing fuel to be forced out the metering jets where it pools in the intake manifold at the base of the carb, flooding the engine with gas.  Too rich a mixture won't ignite.   When you start your warm engine, try slowly flooring the gas pedal (so as not to cause the accelerator pump to squirt even more raw gas into the mix) while you are cranking your engine.  Having the throttle wide open helps clear out the unburned gas that has collected, and lean out the overly rich mixture so the car can start.  

 

If the car cranks over more slowly when it's hot, it could be  a couple things.  Check your electrical connections to make sure they are clean and tight.  Make sure your battery cables are the correct gauge.  Also check your starter.  I found that when my starter got hot from the warmed engine, the shaft would bind in the bushings.    I reamed out the bushings a little to get more clearance, and the starter now spins freely hot or cold.

So the starter turns over as normal. So I’ll give the gas pedal a try. I wonder if trying to clear out the cylinders/intake by cranking it a few times with the ignition off if it would help

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You didn't say what engine but I spose it is carbureted.  if the holding the pedal to the floor doesn't work,  check the spark by pulling the wire from the center of the distributor and holding it 1/4 inch from metal. Use insulated pliers.  Have someone crank the engine. you should get a good snappy spark. if not, you have some tuning to do as above.  Note Zeke's comment. He's right. 

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43 minutes ago, Oldtech said:

You didn't say what engine but I spose it is carbureted.  if the holding the pedal to the floor doesn't work,  check the spark by pulling the wire from the center of the distributor and holding it 1/4 inch from metal. Use insulated pliers.  Have someone crank the engine. you should get a good snappy spark. if not, you have some tuning to do as above.  Note Zeke's comment. He's right. 

Thank you. I’ll check that also. It’s a 1939 201 flathead p7

 

 

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On 5/6/2021 at 12:28 PM, Frijolito said:

So the starter turns over as normal. So I’ll give the gas pedal a try. I wonder if trying to clear out the cylinders/intake by cranking it a few times with the ignition off if it would help

First off, what a beautiful car!  You don't see many of these.   Secondly, I think cranking it over with the ignition off might just draw in more unburned gas.  I'd try it with the ignition on so that as soon as the air/fuel ratio comes to an ignitable mix it will fire off.

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We worked (revived) a 40s Chrysler 6 Traveler many years back, it would start easy and run well over the road for as long as you like with normal temp readings etc.,but shut it down and was EXTREMELY hard or impossible to restart untill the motor substantially cooled..

 We discovered the car had recieved a valve job a few years previously and this not wanting to start hot was the trouble we figured is what retired the car.

What it was,was the valve lash was set too tight or not reset at all.

  We found one exhaust valve was getting burned from to little or no clearance .Replaced it ,hand lapped the valves all back in and reset them all cold plus .002/.003,  all in one day.

Cured the starting issue and ran better then ever.

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