Hi! I am not a Chevy guy, so I probably skimmed right over this originally because I don't like to talk about things I know nothing about. However, I am happy to offer generic advice regarding carbureted motors. So I will do my best.
Hello all, I am having an issue with my 1981 G10 Inline6. It starts up fine and dandy when cold. Once I have driven it around and it gets to operating temperature then it becomes harder to start. It sounds a little weak when cranking and the only remedy I've found is to stomp the accelerator to the floor and hold it there to make it fire up.
It sounds like the problem you are describing is the engine will turn over/crankspin fast when the engine is cold but once the engine gets warm/hot it turns over/cranks slowly. An engine that cranks fine cold but turns over slowly when hot usually is an electrical issue, specifically the starter motor is weak and failing. I had this same problem years ago on my 89 Ford van. My solution was to buy a hi-torque mini-starter and wrap it in some heat shield material. It has been working fine for over a decade without me even thinking about it.
Heat soak can cause a starter motor to get weak and eventually fail. You can try getting a starter motor heat shield kit like I did (thermo barrier blanket secured with a metal zip tie or two) and see if that ake any difference. If it does, then your starter motor is probably getting old and needs to be rebuilt (if possible- try and find a local shop to rebuild your original) or replaced (try and find NOS or used original, don't get a Cardone remanufactured unit, they often are bad).
If the problem is the starter motor, then it won't make a difference if you hold the gas pedal down or not. The carburetor has absolutely nothing to do with the starter motor.
I know this is a common issue on older Chevy's, and I'm inclined to think it is the starter/solenoid, but after reading through forums today I found so many different recommendations online from rerouting fuel lines to carb fuel boiling and on and on. I recently set timing, did plugs, wires, cap and rotor, and had the vacuum lines routed correctly. This is a stock motor. This issue was there before, and still is after the tune up. it does run better and smoother and is not dieseling any longer, but still hard to start when warm. Any ideas that a basic driveway mechanic like me can look into?
I think you are on the right track with your starter motor. As I said above, try and find a local shop to rebuild yours.
It also never hurts to check the basics like your base timing. Also, check the accuracy of your timing mark. I can't speak for GM products, but I know that Ford and Chrysler products put the timing mark on the vibration damper on the end of the crank. The damper is made up of two pieces of metal, an inner section and an outer ring, bonded by vulcanized rubber. After decades of use the rubber breaks down and the outer ring can slip in relation to the center lump or detach completely. I have had both things happen to me. Since the timing mark is on the outer ring, the timing mark can actually not read accurately. You will need a piston stop tool to mark the damper and verify it shows TDC correctly.
In sum- first check your base timing. Incorrect timing can make an engine hard to start when hot. If your base timing checks out OK, then I recommend you get your starter motor inspected/rebuilt.
Incidentally, and I am not trying to be a jerk about this, the term "solenoid" is often used incorrectly by many people when discussing the starting system on cars. The only solenoid in the starting system is the starter solenoid that is (usually) bolted to the side of the starter motor and kicks out the starter gear when the key is turned. That is the only part correctly referred to as a solenoid. Many people incorrectly refer to the starter relay as the solenoid. The relay bolts to the firewall or the inner fender and has nothing but wires going to it. Its job is to take the low amp signal from the ignition switch and use it to turn the high amp battery feed on and off to the starter. When you are describing problems with your car it is always best practice to refer to parts by their correct name. It makes it easier to provide useful advice and to understand the symptoms described.