Truck won't start when it warms up...Help!

My '51 chevy truck is becoming a stubborn mule. I am running a 250 with a offenhauser intake/holley carb and stovebolt headers....the problem I am having is that when the truck is cold it starts right away, runs smooth and no issues ( I can drive it with no problems) but if I turn it off and try to start it back up...it won't start. I have drained the battery trying to start it and nothing, pump the gas, nothing....I wait half an hour/one hour and there she goes again, starting with no issues and riding with no issues.

Any help you can provide me troubleshooting and resolving will be greatly appreciated.

 

Have you tried some engine start? if that works it rules out the ignition. Sounds to me that its flooding when the carb heats up due to heat transfer from the manifold when turned off. JW

 

Not saying this is the answer but we experienced this with my dads Chevy wagon a long time ago and the culprit turned out to be a bad ballast resistor. HRP

 

Vapor Lock- Is there a carb spacer between the carb and manifold?

A vapor lock can happen when the engine is stopped while hot and the vehicle is parked for a short period. The fuel in the line near the engine does not move and can thus heat up sufficiently to form a vapor lock. Under hood temp is also higher when the car not moving.
Do you have any fuel lines running close to hot spots?

 

all my lines are aluminum tubing one might be running near a hot spot...how can I test for vapor lock and/or how can eliminate if this is the case?

Ballast resistor is new but can replace to eliminate posibility.

Haven't use engine start yet but will do next time. Thank you all for the ideas so far

 

could you try a container of gas and some rubber hose just to see if it helps

 

Another possibility is the condenser, I'd swap out points and condenser..unless of course it's electronic ignition.

 

I have had a coil cause similar problems

 

I wouldn't use aluminum lines. Fuel line should be on other side of the engine and come around the front, away from the exhaust.

 

Just my personal experience but I was told that I had a vapor lock problem and then I went to look at a 383 engine and after cranking for several seconds the guy went to the garage, brought out CO2 fire extinguisher, placed his hat over the carb, sprayed it until there was a pile of snow on top of the coil and it started right up. Before spending any money, I'd try a known good coil first. Oh when you get it fixed please tell us what fixed it.

 

Have you tryed to hold the throttle wide open and crank to clear flood it ?

 

http://chevy.oldcarmanualproject.com/shop/1955/55csm06y35.html

 

I had the same thing on a couple cars as well as my inboard boat motor and it turned out to be a crack in the rotor. A simple 5 minute fix and it never did it again

 

Figure out if it is a gas problem or ignition.

If ignition, it could be condensor or coil. If it was the ballast resistor and if the ignition switch by-p***es the resistor, it would start but not run.

If it is a gas problem, it could be flooding out from gas boiling out of the carb when setting or it could be vapor lock. I don't know anything about vapor lock and think it more often than not is misdiagnosed. The gas running out of the carb and into the manifold from the heat of the motor therefore flooding the engine is usually the case for me. Putting an insulator inbetween the carb and manifold helps. Otherwise I just start it as you would a flooded motor, throttle wide open until it fires.

A side note. I have a pertronix ignition on one of the cars and it does not seem to have the problem with flooding. Maybe the hotter spark helps the cause.

Neal

 

You may also need to check the power wire to the coil or HEI. I had one that had broken down and when you were starting cold it would fire right up when hot grind till your blue. The wire would not be hot till you releaced the key to run spot! Just a check with test light.

 

With your intake and header set up, you are not getting under manifold heat from the exhaust. Are you using a water heated intake? If not, what type of choke are you using? Inline engines need a hot intake to work properly, yours may need to cool down enough to get the choke back on. I know mine is a real ***** to start with out heat in the intake.

Joe

 

When it's hot and won't start look down the carburator and see if its wet. Chevy had a problem with inline 6s when hot the fuel would expand between pump and the carb and over power the float valve.

 

Choke sticking closed? What's your timing set ?

 

Question #1 SHOULD BE....do you have spark when its hot?

 

From personal experience: check starter solenoid or ignition timing.

 

I had the exact same problem on my '63 C-10. I found the problem was a poor engine-to-frame ground stap connection. I removed the ground strap at the frame & engine, sanded the contact areas to bright metal, re-attached the strap and never had another problem with hot starting.

 

I troubleshooted all and rule out one by ine to find out the problem I am having is with gasoline. It looks to be boiling once it warms up...

How can I fix this...any ideas?

 

Louvre the hood .

 

As HRP said use carb spacers/isolaters. This will help keep the carbs from soaking up the heat from the manifold while the engine is turned off. Also maybe set the float a little lower to allow for more expansion??

 

Have you checked your compression? I had this problem once and found out I had a lot of cracked pistons. It was losing compression.

 

What he said. Yup, that was very similar to my problem. Inline 6, Clifford intake and headers, Mallory dual point.

Near the starter, I added a #4 gauge ground strap from the bellhousing to the frame. No more problems. I chased this problem for 3 years.

Excellent suggestion.

 

I have had similar issues heat soaking a carb when it sits. A good quality heat insulating spacer will help a great deal. Examine your cooling system as well if you can keep your ride from running hot it will also help.

 

Condenser

 

Hope I am not talking too soon but looks like the problem is now fixed.

Yes, I went at it full force and tried every advice I was told...started with a new coil, it didn't worked. I got rid of the ballast and use a blue coil with built-in ballast, it still didn't work. I replaced points and condenser, nada. I replaced to a different distributor, still nada.
I isolated and grounded the starter, nada. I added an isolator to the carb and besides making run like ****, I didn't gained anything but screwed up the adjustment of the carb.
I adjusted the timing and valves...still didn't help. Rerouted the gas line to make sure it wasn't getting too hot....still nothing.
Checked my grounds to the frame and motor....zip, nada! I replaced my battery to an Optima and it helped a little but no....At tha point I GAVE UP!!! My lack of knowledge and experience wasn't getting me an answer so I looked for help.

Groucho was recommended by Jcapps and with one phone call alone he fixed it. I was missing a wire, the wire that goes from the starter to the + side of the coil. I guess my coil wasn't getting all the juice it needed to start once it got warm. I put the wire and felt the difference at starting right away...Remember, I did my own electrical and it was a first time for me.
After a couple of trials to make sure it was fixed my starter gave out...I guess it was already on its way out. After buying a new one...What a difference it has made. That ****er rocks my engine.

So far so good...I've actually have taken her out on the road and it has performed great...minus the now minor adjustments it needs after I screwed everything up trying to fix it.

I appreciate all the input people had as it helped learned a great deal and also helped me discover other minor issues my engine has that I can now tweak to get her running even better and enjoy my truck even more.

 

Yes the wire is used to put a full 12v to the coil when starting. Otherwise the coil only needs 6 v to run. Good on ya. Thanks for the update!!