Starting Problem When Hot ?

[Ironhorse]

Need some input and ideas on my 71 4x4 LWB. Has 350 V-8 with 2 bbl carb and unknown miles. Does smoke a bit on initial startup after it sets awhile but oil comsumption is not excessive. Drove it yesterday to Wichita and around, total about 45-50 miles. In town traffic and no problems. Stopped to get a cold drink, (Dr. Pepper while driving !) and when I attempted to start the truck it turned over good but did not fire. Have recently rebuilt the 2 bbl carb, new mechanical fuel pump and plug wires. After several attempts it finally caught and ran fine going home. Ran it 60-65 mph with no missing or hesitation at all. Later when I got home and attempted to start again within 15 minutes after arrival, same thing. Turns over fine but would not fire. Let it set for 30-45 minutes and started fine. Do I have a coil that is weak? Still has the breaker points ignition. Is there some way I can test the coil? Still has GM old style round coil but don't have any idea as to how old it is. Bad condensor in the distributor? Have a out of town truck show coming and don't want problems going or coming home. Any ideas or input is appreciated.

[old Rusty C10]

could be the coil or it could be the resistor int he distributor had that drive me nuts for a while in my old 72

[Ironhorse]

Thanks Bob, have several old coils laying around. Any idea as to how I can check them for operation short of installing and hope that fixes the problem? Any other input from you electrical guru's out there.

[gr8scott51]

How hot is it outside? Quite often, older, carburated enigines will vapor lock (gas flashes before it gets to the carb). Often, after letting the engine cool, the problem goes away and the engine will start again. Make sure your gas lines aren't too close to your headers and not contacting your engine or other heat source. You can even wrap them in foil to prevent some heat transfer. Just a possibility.

[Ironhorse]

Thought about the vapor lock bit but the fuel line that runs from the mechanical pump to the carb is original steel line and sits about an 1" to 1 1/2" away from the block. I can wrap it in some sort of covering but the temps are only in the mid to high 80's. Would not think that would be hot enough to give a problem?

[gr8scott51]

....but, is the engine temp okay? If you have a thermostatically controlled fan, it may be malfunctioning and raising the temp under your hood. Grasping at straws here. Good luck, Scott

[barn9]

Vapor lock was my first thought also, but I agree with Gary, it wasn't that hot around here yesterday. I'd say it's time to get an HEI, and get rid of that archaic distributor. Have you got that big cooler ready for the 22nd Gary?

[71GMC_3/4T]

Check for spark the next time it won't start. If it has spark, check to see if it squirts fuel when you move the throttle.
When it does start, does it blow lots of black smoke, like it was flooded? If so, then your problem is likely ignition.

To check your coil, measure it while it's cold. Then throw it in the oven at 250 for an hour and measure it again. You want to measure the primary from screw terminal to screw terminal. Measure the secondary from the HV socket to the metal can. The resistance may change some, but if it goes open or shorted, then you have a junk coil.

I agree with changing over to HEI. Simple way to fix a lot of headaches.

[tom hand]

Or does the motor still have the heat riser valve on the exhast manifold? If it sticks closed it could overheat the carb, (its designed to warm up the intake when it's cold) causing the gas to boil in the carb. One pipe blocked on a dual exhaust would do the same thing. Next time it does it pull the breather and see if the accelarator pump will sqirt gas to help tell if it is a fuel or ignition problem.

[Ironhorse]

Thanks guys for the input. Gives me some ideas to look for. First off need to get the truck clutch/ Z-bar back together. Keeps sliding out of the slot in the frame side bracket. Always something I guess.

LB, have the cooler setting and ready to go! Sent my pre-registration fee in Weds. Hope I get the truck back running and dependable before. What time does the show start? Any luck on the parking situation for the 67-72 truck bunch?

My son (works at local O'Rielly's) agrees on the HEI dist. ("Get rid of the points, Dad !" Your stuck in the 70's")

[ZOOMY]

All of the above tries, but also it might be flooding out from a bad needle seat causing excess fuel to drip into the inrtake. Next time it won't start hold the gas pedal to the floor to give it lots of air.(don't pump it). If that doesn't work I'd go back to the ignition.