4v carb question

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Nov 24, 2002 | 05:11 PM

jbulson

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From: Farmington MN U. S. A.

4v carb question

[updated:LAST EDITED ON 24-Nov-02 AT 06:13 PM (EST)]I have a holley 4150 4v carb on my 360. Why are there 2 mixture screws? Is one for primary and the other for secondary? I have a slight stutter on the bottom end, sometimes (when cold) it will even back fire. But the top end is fine. Any help is awesome!

Nov 24, 2002 | 06:11 PM

Ratsmoker

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From: Missouri

4v carb question

The left screw is for the left primary and the right screw is for the right primary. It sounds as if you are running too lean. The best way to set your idle mixture is with a vaccum guage attaining the best possible vaccum. You can also turn the screws out to richen it just to the point where the idle stops increasing and everything smooths out.

Nov 24, 2002 | 07:24 PM

jbulson

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From: Farmington MN U. S. A.

4v carb question

so both screws should be turned out the same amount. Are they REALLY sensitivr? I have been turning them in 1/8-1/4 turn increments and am still haveing trouble on the bottom end...also, Where can I purchase an vacume gauge..the local parts stores dont seen to stock them..And when I find one what should it read?

Nov 25, 2002 | 12:11 AM

Ratsmoker

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From: Missouri

4v carb question

What it reads depends all on yor engine setup but should be in the 12 - 19in hg area. The screws should be pretty close to the same number of turns. You should go with 1/8 at a time. They are pretty sensitive. Autozone carries them. I can't believe none of the other parts stores by you has them. You can always order from summit or carparts.

Nov 25, 2002 | 07:20 AM

William

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From: Sun River St. George

4v carb question

Stumbling crappy running Fords ain't usually caused by idle screws. In fact, 99 times from 100 it isn’t the carburetor causing the fault. I guess it’s just easier too grab a screw driver and fiddle with the air screws. Start with a complete ignition tune up! This doesn’t have to be expensive either. Pull and gap the plugs, clean the contacts in the cap and wipe it out with WD40, clean the rotor tip and apply a little dielectric crease on the end and spring. If you still have points replace them and the condenser. If you have electronic ignition just wipe crap off the recular (sp) and pickup. Inspect the plug wires for leaks and broken ends. Then fire it up and set the ignition timing and dwell. Bet the problem goes away! If the cap, rotor, plugs and wires are more than 25K miles consider replacing them. Check the rubber hoses and plugs for dry rot and be sure the vacuum and centrifugal advance mechanisms are working. Then the last thing you should do is adjust the air screws, curb and cold start idle. Post back!
William in Atlanta

Nov 26, 2002 | 09:59 PM

jbulson

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From: Farmington MN U. S. A.

4v carb question

I did A tune up not long ago and did see some improvment. However as I failed to mention in earlier posts, the reason I am adjusting screws is because I have black smoke and strong exaughst. I also have a vibration (somehow engine related) between 2000-3000rpm, and a low end stutter. The distributor,cap,rotor,wires and plugs are all fairly new. I know my engine is old and tired but im trying to make do with what I have.

Thanks for the advice!!!!

Nov 27, 2002 | 07:21 AM

William

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From: Sun River St. George

4v carb question

Black smoke is unburned fuel. Timing is advanced or retarded, choke is stuck or icing, carburetor float is set wrong or the needle valve is sticking. You may have crossed plug wires. Does any of this clear up when the engine is really completly warmed up? What thermostat are you using in Canada 190 is good 195 is better. These engines will run really good with low compression, worn bearings and such. It may be worn out but solve this problem and it may last for years.
William in Atlanta