Farm Equipment - HELP WANTED on carb issue!

Print Page | Close Window

HELP WANTED on carb issue!

Printed From: Unofficial Allis
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=7179
Printed Date: 28 Jul 2025 at 5:23pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com

Topic: HELP WANTED on carb issue!

Posted By: mark-east-tn
Subject: HELP WANTED on carb issue!
Date Posted: 25 Jan 2010 at 8:45pm

I have a Zenith 7078-C carb. that is dual fuel for my 35 WC , I have back together with a rebuild kit and gaskets and have put it on the tractor . how many turns out on the air and fuel needle for it. The carb kit didnt have any info with it and I have almost had the big one trying to hand crank it. It has new paint and just cant bear to pull it off and the new engine dosent help matters. thanks for the help ! Mark-east-tn

Replies:

Posted By: AndrewGubbels
Date Posted: 25 Jan 2010 at 8:50pm

You want to turn it clear in and then back out about 4 full turns. That is where ours is set and it runs really well. One thing that is probably not helping, if it has set for awhile everything is so dried out in the manifolds that it will take some cranking to get everything as it should to fire. I hope this helps.

Andrew

-------------
Andrew Gubbels
Gubbels Restoration

Posted By: Gerald J.
Date Posted: 26 Jan 2010 at 10:14am

The preset is only close enough to make it hopefully run so you can refine the adjustment running.

Gerald J.

Posted By: Dick L
Date Posted: 26 Jan 2010 at 1:20pm

Just remember one adjustment has nothing to to do with the other. The small adjustment is for the idle adjustment. You can turn them both out 2 or 3 turns the when it starts you adjust the idle first. You want to alternate small adjustment between the needle and the stop screw on the butterfly lever at the back, working the throttle lever down/back. You want to get it to run as slow as you can get it to run without stopping. That will take a little fussing and restarting of the engine.

When you get the idle where it needs to be then open the throttle wide open. You then adjust the power jet to the highest RPM. Then you turn the adjustment screw until you notice a slight lower RPM.

Thats alls theres to it.

The idle adjustment screw adjust the air with the fuel for idle only.

The higher RPM's draws the air into the engine and the power jet adjusts the correct amount of fuel into the air stream.

Posted By: Dave(inMA)
Date Posted: 26 Jan 2010 at 6:19pm

Dick, for some reason that description of adjusting a carb is about the clearest I've ever read! Perhaps it's just your choice of words, I dunno. Thanks.

-------------
WC, CA, D14, WD45

Posted By: Gerald J.
Date Posted: 26 Jan 2010 at 6:51pm

If you do not get the speed really slow for the idle adjustment (e.g. throttle plate closed tight) there will be interaction between the high and idle mix adjustments so you have to do the sequence several times to get it optimized. Then setting for maximum engine speed lightly loaded near the normal maximum rated engine speed, but unloaded does not use fuel like being loaded and it may take a bit of tweaking under load to get maximum power. Maximum power will be on the rich side of the fastest running.

Gerald J.

Posted By: Rogers
Date Posted: 26 Jan 2010 at 8:31pm

1. For a Zenith carburetor you start at 1-1/2 turns out on the upper air needle and 4-1/2 turns out on the lower gas needle. This should be good enough to allow the engine to run.

2. After starting open the engine to about half throttle and let it run for a minute to warm up.

3. Close back on the lower main gas needle until the engine begins to run lean starving for gas.

4. Start opening back up on the lower gas needle until the engine begins running rich keeping up with how many turns you opened it back up.

5. Leave the main gas needle set half way between lean and rich.

I have found that the final main gas needle adjustment is about ¾ to 1 turn open from where the engine started starving for gas, and the air needle ends up staying at 1-1/2 tuns out.

-------------
Think for yourself and be your own expert. Be willing to change your mind; however, willingness to change your mind doesn’t mean that you will. Blindly following any path is the pinnacle of insanity.