Argh! Stumble off idle with new parts?!
 

So I have a brand new crate engine, a professionally rebuilt Rochester quadrajet carb, new fuel pump, new accelerator pump, and mostly all new parts in my car. Engine is timed at 10* BTDC and fast/slow idle set to recommended specs.

Engine runs like a dream, except for the stumble off idle. Damn. I have narrowed it down (I think) to my fuel mixture being too lean, but I need some opinions and advice to be sure. And I forget: is turning the screws in clockwise = more air or more fuel?

...This is where the Haynes manual fails - "adjust mixture as necessary." Er, ok, great directions there, Lou...

Re: Argh! Stumble off idle with new parts?!
 

Kix: Idle mixture screws meter only fuel. Unscrew, back out, counter clockwise rotation, whatever = richer. "Q" jet idle screw settings about 3.5 to 4 turns out from seated. jim

Re: Argh! Stumble off idle with new parts?!
 

AFAIK, those screws only effect the mixture at idle.

Look here under "Air and Fuel Delivery."

http://www.73-87.com/7387garage/garage_drivetrain.htm

Slonaker

Re: Argh! Stumble off idle with new parts?!
 

All right, I will try turning them out a 1/4 screw at a time and see if that helps any... could it also be a function of a new motor still settling in?

I don't want to jump the gun here so I'm checking all my options. It's hell being a new truck addict and a worry-wort :lol:

Re: Argh! Stumble off idle with new parts?!
 

I had similar symptoms with my engine in the summer, upped the initial timing to 14*BTDC and reset the idle mixture with a vacuum gauge and all was peachy.

Re: Argh! Stumble off idle with new parts?!
 

What kind of engine are you running? The recommendations that came with this engine was 10*. I think it's actually at 11* because I don't have a digital timing light but it's close.

Maybe it's my imagination, but it seems less pronounced now. I'm still going to richen the mixture slightly and see if my performance is any better...

Re: Argh! Stumble off idle with new parts?!
 

It was a '79 350 block with stock heads ported by me, Melling RV/towing cam, Offenhauser split-port intake and a spreadbore double-pumper Holley carb, stock HEI ignition. I've been told cam is the same as the Edelbrock Performer cam, for which Edelbrock recommends 14*BTDC when ran with stock HEI ignition, so that's what I did and it was all it needed to start running beautifully.

Also when playing with the idle fuel mixture tis best to read off a vacuum gauge, so hook one up to the manifold if you haven't done so already.