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Allis c zenith carb setting

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Topic: Allis c zenith carb setting

Posted By: ymhajoe
Subject: Allis c zenith carb setting
Date Posted: 02 May 2011 at 11:26am

I have an AC- C with a Zenith carb on it. It only has one screw on it to adjust. Is it an idle mixture screw ? How many turns out should it be set at ? Thanks Joe

Replies:

Posted By: cmsmoke
Date Posted: 02 May 2011 at 11:59am

If you are talking the screw in the middle of the carb. throat that points slightly up on an angle...Yes that is the air mixture screw. There is no set # of turns for every "C" engine out there.

This is how I do it...Set your idle to about 450 rpm's, or as low as it will idle without shutting off. Then turn the air screw to achieve the highest idle speed. Turn the screw back in until the engine speed changes, then reopen it a 1/4 turn. Reset your idle speed.

Mine is about 1-3/4 to 2 turns out. The condition of your carb. and engine will vary the setting.

Posted By: Dick L
Date Posted: 02 May 2011 at 1:40pm

You have the settings mixed up cmsmoke. What you just stated was for the main jet adjustment when you have one. The idle screw is for idle only. The slight opening for the butterfly is set by the stop screw on the back. The stop screw sets the rpm. The idle mixture screw is set to make the engine run smooth at the stop screw setting. Both the idle screw and the stop screw has to be tweeked a little at a time to find the smooth running low rpm. Above idle you can remove the idle mixture screw and it will make no difference in the running of the engine because you are then drawing the fuel thru the main jet.

If you have an adjustable main jet you would then open the throttle and adjust until you had the highest run rpm's and then retard the screw until you could see a slight drop in rpm's. slight is the key word.

Posted By: cmsmoke
Date Posted: 02 May 2011 at 2:21pm

I don't have anything mixed up. Ymhajoe asked about the idle mixture screw...Which is the same as the air adjustment screw that I described and refered to. The adjustable main jet (when equipped) is in the bowl section. Ymhajoe doesn't have one as he stated with his only having one adjustment screw.

The information I gave is good. Don't be afraid to use it.

Posted By: Dick L
Date Posted: 02 May 2011 at 9:42pm

You are correct. It will work and run just fine the way you said to adjust it.

Lets say we were both setting our idle speed and was about to enter a slow tractor contest. After I achieved my smoothest slowest rpm and stopped tinkering. You would keep adjusting and bring up the rpm's. I would win the contest.

Posted By: cmsmoke
Date Posted: 03 May 2011 at 5:02am

I doubt it, Dick. The smoothest idle achieved adjusting the air screw will also be the highest. That is why I state to "Reset the idle speed".

Did ymhajoe ask how to win a slow contest?

Sorry for turning you question into a p###ing contest, Ymhajoe. How did you make out?

Posted By: ymhajoe
Date Posted: 03 May 2011 at 4:27pm

I did what cmsmoke said in the first reply and ended up at about 2 1/4 turns out and seems to be idling just fine now. Thanks so much for the help I need to get mowing. Ymhajoe