1977 Won't start


#1

Got a old chevy pickup, that is rarely driven (10mpg): once per week. It is very hard to start. Mechanics are stumped. Latest try was cleaning the carburator. It turns over happily, but does not catch. Pumping gas pedal and holding it down helps but it still takes a long time to catch, and then must warm up several minutes before it will run without stalling.


#2

How was the carb cleaning done? Simply spraying Gumout over and into the carb will not do the trick. A real carb cleaning requires disassembly. Then, parts can be inspected for wear and damage. It sounds like either a worn-out carb with a bad choke, or in bad need of a tune-up (plugs and wires, cap and rotor) and a coil check.


#3

You might want to check if the choke is working correctly.

Remove the air filter cover. Now step on the accelerator once. The choke plate should be fully closed. Now start the engine, The choke plate should only open slightly. If it doesn’t, there’s a problem with primary choke pull-off diaphram. If it is open slightly, then try reving the engine. Each time the engine revs, the choke plate should open and then close when off the accelerator. If this doesn’t happen, the secondary choke pull-off diaphram is defective. Now let the engine idle. The choke plate should start to open until the plate is in the verticle position. If this doesn’t happen, there’s a problem with the thermal choke spring.

Tester


#4

How are the plugs and wires? Coil? Is this electronic ignition? Timing? Pumping the gas pedal points to Tester’s suggestion, but on this age truck I’d check the electrical stuff too. Rocketman


#5

Sounds like you have two problems. The carburetor is “leaking down”, that is, the float bowl has an internal leak which drains the carb over a period of time. So when you try and start the truck,there is no fuel available. It takes considerable cranking to get the crude fuel pump to re-fill the carb.

Then, after it finally starts, the choke is not working properly, as Tester correctly detailed…

Try priming the engine by pouring 1 ounce of gasoline down the carb throat before you try to start it. If it fires right up, then perhaps stalls, FOR SURE, the carb needs rebuilding, including sealing the welch plugs, a potential source of leaks…


#6

I would replace the ignition module and check for frayed wires on the pickup, or just change them both without checking anything else, and get rid of the old coil too.