Pulling Forum - Carburetor Guys

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Carburetor Guys

Printed From: Unofficial Allis
Category: Other Topics
Forum Name: Pulling Forum
Forum Description: Forum dedicated to Tractor and Garden Pulling
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=103579
Printed Date: 25 Nov 2024 at 2:54am
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Topic: Carburetor Guys

Posted By: dgerth
Subject: Carburetor Guys
Date Posted: 22 Mar 2015 at 5:51am

Gentlemen,

I have a TSX -853 carb that is giving me fits. I have it on a CA, for pulling, with a 160 cid motor wit about 12:1 comp. It is timed with a vacuum gauge to 22 in. of vac, points are set at .020, float is at 1/4 inch rise. The problem is that it will not idle below 800-900 rpms. Trying to go any lower results in the engine dieing with a hard restart. It pulls strong on the higher end, but will not idle well. When decellerating from the high end, to idle, it will also die. The carb has been soaked overnight in solvent and is clean enough to eat from. Is there still blockage internally or do I need to drill out one of the jets or other mods? Is this carb enough or too much for this engine? I use the same on a WD 240 engine with good results. What possibly could be the problem?

tks for your help with this.

dgerth

Replies:

Posted By: PaulB
Date Posted: 22 Mar 2015 at 6:09am

I sounds as if the idle circuit is not functioning properly. With the carburetor adjusted as you want it, take it off and see if the idle slot (or hole) is exposed. If not it will have to have the slot cut further, or if you have an idle hole, drill a small hole in the butterfly so the idle screw can be backed out some. With that much compression, the fuel curve will definitely need to be altered. Do you have an exhaust temperature gauge on it to see if your're getting the fuel you need? How may degrees is you static timing? What is it at full speed?

Posted By: DrAllis
Date Posted: 22 Mar 2015 at 8:35am

I would try it on a different (240) engine and see how it acts and proceed with repairs and changes from there.

Posted By: Hudsonator
Date Posted: 22 Mar 2015 at 12:11pm

For whatever reason, most slow speed circuits in tractor carbs do not work right anymore. I have had to correct every single one in the home fleet. They run way too lean and have caused overheating and head gasket failure. The "gasoline" fuels these days must be more viscous, or harder to pull through the emulsion systems, than when these carbs were originally designed.

Of course, no cure helps a dirty carb/circuit - so make sure its all clean.

I've had to open up the air bleed jet on the idle/low speed circuit at least .003" on about any carb I've touched for whatever purpose. While the common knowledge is larger air bleed = leaner mixture, it appears as if the air bleeds are so small that not enough vacuum signal is being transferred to the low speed circuit for it to work as it should. Hence, .003" larger and then the normal rationale regarding bleed tuning seems to start applying.

On a marvel, its the tiny brass jet in the top half of the carb. Most of them are .030 to .032" stock and I'll open them up .003" to start with and go from there. The smallest air bleed jet I've encountered on an Allis was a Zenith replacement carb on a D14 @ .028", same .003" increase straightened it right up.

You know you've got it right when your tractor is idling with no skipping and the idle mixture screw is between 3/4 and 1 full turn out with max vacuum.

If you have a buddy in the heating/cooling industry with some gauge drills for propane/natural gas orifice tuning - they are the best to use to step up your jets a tiny bit at a time.

-------------
There isn't much a WC can't do.

WD's just do it better.

Posted By: dgerth
Date Posted: 25 Mar 2015 at 5:54am

Posted By: dgerth
Date Posted: 25 Mar 2015 at 6:02am

Gentlemen,

Don' t know what happened to the first one, I'll try again.

I took the Doc's suggestion first and swapped the carbs from the CA and WD and so far, that seems to have cured the problem. They both run and idle as they should. Haven't pulled them yet but have a practice pull coming up to test.

Thanks guys for the input.