Car is running rich, Carb or timing?

[Mean Gene]

My 440 has a new Holley 750. Running very rich. How should I go about leaning it out? Carb adjustments or timing?

Thanx guys!

[dwc43]

Timming wont lean out a rich mixture at all. You need jet and/or power valve changes.

[dave571]

Depending which series of holley, there are a lot of adjustments you can make.

Assuming it is a model with metering blocks on both ends, you need to take off the float bowls, and change the jets.

The jets are the small round brass fittings with the tiny hole in the middle. two on each metering block

Pull them out and see what number is on them. The number is the size of the jet, in thousandths of an inch.

You want to go smaller. If it seems way rich then I would go 4 sizes smaller.

Try to keep a 6 to 8 point(preferably 8) spread from front to rear. Ie: if you presently have 80's in the front, and 86 un the rear, try 76 up front, and 84 in the rear.

[TrashedCharger]

If your timing is off (it won't affect air/fuel mixture) it needs to be set correctly. You should use a timing light with adjustable zero degree display so you can check your total advance at wide open throttle as well as base idle.

Dave is right about the separation between front and rear jet sizes. Having smaller primary jets gives your car more drivability and correct air to fuel ratio at cruizing speeds, where a larger jet in the secondary ciruit gives the car the needed extra fuel under wide open throttle and the higer ends of the throttle.

While you have the float bowls and metering blocks out and the carb is apart, you should go and buy a power valve saver if you plan on keeping that thing.

Honestly, I don't like Holley carburetors on anything but a non choke race engine. I just don't like their float bowl and power valve design. The best carburetor for a mopar in my opinion is the Thermoquad, but they aren't without their downfalls either. It's hard to get a tuning kit for them and you can't buy a new one. The Carter AVS is an excellent street carburetor because of it's rear secondary tunability.

Just go pick up a jetting kit for that thing and follow the instructions for your altitude and cubic inch displacement of your engine and you'll be fine.

[Mean Gene]

Well, I do have a Thermoquad on the shelf in the garage....

[dwc43]

Originally Posted by Mean Gene

Well, I do have a Thermoquad on the shelf in the garage....

Good choice. We used them even on our dirt track cars.