1985 GMC 305 Won’t Stay idling

[Doc C]

My 85 GMC High Sierra with the carbureted 305 will not continue running after cranked. It coughs deeply then dies. I have to hold the accelerator down to keep it running. But even then, it dies. I have looked at adjusting the fuel mixture, but cannot find the screws. Any ideas? Or is a new carburetor the simple but expensive fix?

 

[Trucksareforwork]

Still a quadrajet?

I have the same motor. In no particular order…

1. Fuel filter(s) clogged? Have to check the one where the fuel line goes into the carb.
2. Vacuum line loose or broken? Might be a problem. Lots of possibilities for vacuum leak on the stock configuration.
3. Check choke function and adjustment? Might be too rich. Might be too much choke for too long. Does the choke pull off work? Check the vacuum line to it.
4. Is it just basically idled to low? Either the regular idle screw or the high idle screw may have broken or been accidentally adjusted wrong.

I don’t think your idle mixture screws would have suddenly caused a non running situation.

 

[Ricko1966]

You know carbureators and carburator adjustments are not the only things that cause vehicles to not idle,or die. Why have you immediately decided its carbureator. And even if the mixture screws need adjustment they aren't the main problem right now. If it wont stay running with throttle some thing else is going on. How did your oroblem start?

 

[Chevy 88]

Just for fun, can you send a picture of your license plate, with your hands showing a "peace sign" in view?

 

[Turbo4whl]

I have looked at adjusting the fuel mixture, but cannot find the screws. Any ideas?

The idle mixture screws on the the last few years GM used Rochester's, before fuel injection, the screws were sealed off.

Read the posts from @Trucksareforwork and @Ricko1966 Idle mixture screws are not the problem.

 

[Broken85]

Check the manifold gasket under the carburetor. I had the same engine. Started the way. If it’s pulling air past a bad gasket, it will never run