What will cause a 305 gmc to shut off after running for 30-45 minutes starts but will not stay running replaced knock sensor plugs cap rotor timing chain and gears timing is adjusted?

Answer 1

It could be that your choke on the carb is not staying open.Once the engine heats up depends. if late model you could have a faulty sensor sensor opens up as it gets warmer. it could also be a number of reasons, like a faulty MAP and/or MAT sensor, faulty ECU/ECM, or your TPS. check the choke -----

Answer I agree about checking the choke and the other sensors, but I think something else is happening. You should also check your exhaust system: a partly plugged cat convertor or a crimped/bent tailpipe can slowly produce enough back pressure to stall an engine.

One other thing: my son's 305 had a quadrajet with the fuel filter inside the fitting at the carb: it would slowly clog up, then as the particles fell off, it would eventually restart. Remove the filter there, and use an external inline one!

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Answer Everything happening here to your 305 has happened to me on my 83 Silverado. I went up and down checking and replacing all of the above mentioned. As it turned out there was a combination of problems causing the stalling. First, the ignition module was failing, as the truck ran and heated up the module would shut the truck down.. once the truck cooled off, ran normal for another 30-45 minutes. Second, to avoid ruining a new module I replaced the coil at the same time, and capacitor just for peace of mind.. while I was under the cap I also cleaned all the corrosion and rust from the ground as to avoid ever having to pop it off due to a "no spark" issue. This helped me tons until the truck started starving for fuel.... I replaced both fuel filters, the one located in the carb and one external in-line, additionally I replaced the fuel pump and pump push rod (again for peace of mind since they're so cheap.. why not?)... my end result - Carb Problems. Ha! Adjusted carb, gone. Truck Runs Great.. hope this helps you.