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Author Topic:   Holley 4412 on the Road
Dirt Forum Racer

Total posts: 90
posted October 29, 2001 09:55 PM
Ok all you major carb specialists. I need some initial tutoring on what is the factory jet size that is supplied in the 4412. Put the carb in my truck (60 over 350, stock(ish) cam, headers, good exhaust,etc.) I have 71's in it now and the plugs look a tad on the dark side, but not that bad. Seems like it's loading up though in certain ranges and from the accelerator pump. More than just being a jet size off, etc. Any constructive advice would greatly be appreciated. Thanx.

Dirt Freak

Total posts: 408
posted October 30, 2001 07:30 AM
Some possible things to look for that may be causing your troubles are:
-A blown power valve, or simply the wrong one for the application.
-Accelerator pump pullover due to the relatively high manifold vacuum
Hmmm...let's see...Possibly check to see that your idle air bleeds (the outer ones) are clear, as well as the mains (inner ones). Either being clogged will cause an overly rich condition.
Also, check to insure your idle mixture "skroo's" are functioning properly and are in the range of 1.5-2.5 turns out from lightly seated.

I'd say a good starting point for that motor would be around a 70-74 jet and a 6.5 power valve. But the jetting can vary greatly due to the air quality (temp, humidity). Some motors and areas of the country will require somewhat smaller jets, tho. It sounds like your condition isn't solely related to jets there, and is possibly more of a pullover problem or something as simple as incorrect float level (should be just at or below the bowl sight plug), or incorrect fuel pressure (6lbs average is fine).

Another thing to think about or confirm is that your ignition and timing are properly set and working as they should. Weak spark can cause innefficient burn at the plug or fool you into thinking there's a carb problem.
Just some stuff that comes to mind anyway...
Hope that helps.


[This message has been edited by KPLugnut (edited October 30, 2001).]

Dirt Forum Racer

Total posts: 90
posted October 30, 2001 10:06 AM
Thanx Lugnut. I have thought about the power valve this morning. I have already gone through the float level, mixture scroos (which work quite well, sensetive),no manifold leaks, and ignition timing. I'm not running the vacuum advance dashpod and have initial timing locked down at 13-14 degrees BTDC. You mentioned about pullover. The engine has excellent vacuum and I wondered about that effect even through the boosters. One thing I did do last night was to loosen my accelerator pump. I was noticing it was flooding/bogging the engine initially which led me (with the booster thought) to believe I had a jetting issue. The engine purrs at idle and will come alive when dropping your foot into it. It's just that range of cruising along when it's experiencing a surge. I had an Edelbrock 600cfm on there and was really getting bit with fuel mileage. Was thinking of a well tuned 4412 would do the all around trick on the road (towing/cruising).

[This message has been edited by smayo964 (edited October 30, 2001).]

Donnie Ross
Dirt Maniac

Total posts: 109
posted December 01, 2001 07:11 AM
you might try putting on a 30 cc pump instead of the stock 50 cc one, and try using vacuum advance it really is helpful on
a street motor.

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