Inliners International Forums General Discussion Electrical Starting Problems wit GMC 6

GMC 302 has trouble starting after it's hot and then turned off. The starter turns the engine for a few fast turns and then disengages.
Usually it takes 4 to 8 tries to get it running.

The GMC engine starts almost instantly when the car has been sitting for days. I pump the gas once and choke it slightly.

The intake system consists of 3 recently rebuilt Weber 32/36 carbs on a home made intake. The center carb has a manual choke. The ignition is HEI with initial mechanical advance set at 10 degrees.

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Starter issue perhaps?? Solenoid failure or maybe the bendix drive is faulty. My old Willys Jeep had that issue and I had to replace the Bendix drive.

I'd say the engine is almost starting and kicks out the starter. Since it works fine when cold it may be caused by too much heat or space in the intake and fuel evaporating in the manifold. Have you tried pushing the throttle wide open while cranking?

I have tried to start it while holding the gas pedal about half open and that seems to work. I starts with a bang and pop and then races until I let off on the gas. I think this indicates more air is needed or too much raw gas is in the manifold.

I tried leaning out the idle mixture screws (tightening them) on the three carbs. Finally got it to restart hot when the screws were set at 1/2 turn out from the closed position.

Well, at least it starts. It is nice when they just pop right off. My '53 with a 270 and 4bbl needs to crank a while sometimes when it is hot. With the foot starter, standard trans, and an E-brake that doesn't quite work I need another foot.

REDLINE of Torrance, CA. sells Weber carbs and parts. Their rule of thumb for idle jet sizing to get a smooth idle is: If you have to set idle screws more than 1 1/2 turns out, your idle jets are too small. And, if you have to set them at less than 1 turn (like me), your jets are too large. So I plan to buy a set of smaller idle jets.

Is your starter button still divorced from the ignition circuit on the key?

I am running significant initial advance - which can lead to (and my case does result in) hard starting when hot. It is as if the initial firing cylinders are pushing back against the starter motor when cranking with the coil on.

To prevent this I hold the starter button down until the engine is spinning as fast as the starter will turn it - and THEN engage the ignition circuit with the key. Works like a charm.

I finally got my GMC starting problem fixed. It turns out my alternator was slowly pooping out. Finally, on a 100 degree day with the AC going, the 40 Chevy quit and would not start with out a Jump. Once running to would generate about 7 amps vs. the 12.7 amp standard but the car ran good enough to drive home. I replaced the 55 amp alternator with a 90 amp version and everything works. My AC, Radio and Radiator Fan additions put extra load on my old alternator and it burned out - I think.