Motor stumble in the trail rig??

[mtnman210]

500 caddy with a quadrajet. Idles fine, maybe a little rich, runs great from 700-3000rpm. above 3000 it starts to stumble, cough, bog and above 4000 it almost dies.

Where should I start problem solving?


Side note it could be timing but I went to check that and there are no timing marks on the balancer anymore. How can I go about setting the timing with no marks?

 

[shady]

find TDC on the compression stroke and put a tape on it with the timing marks. summit and jegs both sell them cheap.

 

[tRustyK5]

Starving for fuel maybe...check fuel delivery. At that rpm I wouldn't suspect timing at all. Any timing issue you might have would be more apparent at lower rpm's IMO.

Rene

 

[mtnman210]

Starving for fuel maybe...check fuel delivery.
Rene

it's the stock fuel pump and carb. Fuel filters are both new. Can I put on a fuel pressure gauge on the inline fuel line into the carb. What else should I check with fuel delivery.

 

[tRustyK5]

I would say you need to see 5-7 psi, but also good volume. Pressure is almost irrelevant without the needed volume. I don't know how to check volume on a mechanical fuel pump.

I guess a way to confirm or deny is to run the motor up to 3000-4000 rpm but not WOT (under load of course), then again at WOT (again under load)and compare. If it acts exactly the same it's definitely RPM related, but not necessarily fuel delivery related. If it's acts a lot worse at WOT I would more strongly suspect the fuel pump or other restriction in the fuel system. For what they cost I'd probably try a new mechanical pump and see if it helps. Worst case you're out $25 and a little of your time.

Rene

 

[mtnman210]

Thanks for the input I'll start with this and see what happens