Farm Equipment - dialing in Zenith idle mixture screw

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dialing in Zenith idle mixture screw

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Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=190764
Printed Date: 07 Aug 2025 at 6:19am
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Topic: dialing in Zenith idle mixture screw

Posted By: Chad_in_PDX
Subject: dialing in Zenith idle mixture screw
Date Posted: 18 Sep 2022 at 10:21pm

I’ve got a B that I’m still getting familiar with.

What is the process for dialing in (leaning out) the idle mixture? Right now my mixture screw is backed out 1.5 turns. This is on a Zenith 10698A. Going by smell, the engine is running rich. Also, the plugs are starting to get sooty.

Thanks

Chad

Replies:

Posted By: Steve in NJ
Date Posted: 20 Sep 2022 at 7:39am

Usually, one and a half is a good starting point for the air/fuel adjustment. Every engine is different for adjusting to get that "right" spot, but if you're blowin' black smoke with the mix screw only 1 1/2 turns out, you might have a high float problem, or junk stuck in the needle seat causing the engine to run rich. The Carburetor might need some attention internally. It might have a lot of rust n' junk in it causing your rich issue..... HTH

Steve@B&B

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39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife