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Farmall M Runs When Chocked - Need Help

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Posted by Sparetime on November 22, 2009 at 15:46:17 from (

Greetings fellow antique tractor enthusiasts! I'm writing my first post in this forum in need of some assistance or advice. I'm trying to resolve a problem with a 1948 Farmall M. In a nutshell, I can get the tractor started, but in order for it to keep running it must remain nearly fully choked, otherwise it will stall out. I can keep it running by tweaking the choke for several minutes in this condition, but have only done so for diagnostic purposes. Throttle movement during this time has no effect. The tractor runs reasonably smooth (ignition, timing, etc. all seem OK), but obviously not correctly in this condition. After multiple searches in these forums for clues to the problem and having made several attempts to resolve the problem, I'm rather stumped. Iím by no means an expert on these and have been learning some as I go. I am reasonable mechanically inclined and have some experience with an Allis Chalmers B also (learned to love and hate magnetosÖ.but thatís a story for another forum :o ). Iím fairly comfortable with working on/diagnosing problems, although Iíve not done major engine repair or teardowns. I'll detail what has been attempted thus far and provide some more general information on the tractor itself.

Tractor Details & background:

- 1948 Farmall M (Serial #FBK-169321X1) with gas engine, distributor/coil ignition (non-magneto) & standard governor (don't know exact type).

- Carb. is IH E12 updraft model #50983DC with 8557D throttle body.

- Tractor is kept outside year round through four season conditions and has been for several years.

- Tractor was running fine last Fall, but sat through most of the winter without being run. I'm fairly sure the gas was run out of the bowl in late Fall in prep. for Winter to avoid any moisture/float issues.

- Had major engine rebuild in mid-90's by previous owner and has probably had approx. 150-200 hrs. run time since

Work done thus far (in no particular order):

- Completely removed, disassembled & cleaned carb. (except venturi port removal from throttle body) with carb. cleaner and compressed air. Disassembly included all jets/ports, etc. No obvious signs of blockages. Fuel line inlet filter was a bit dirty, but was easily cleaned. Carb. ports were subsequently cleaned/inspected several times after uninstalling/reinstalling carb. and experiencing similar poor running conditions.

- Replaced needle valve and seat with kit purchased at Tractor Supply Company (I know some may debate the quality of parts in this kit, but on inspection/installation they looked identical)

- Tested float for leaks (had no fuel in either float and did hot water immersion test - no bubbles)

- Replaced float bowl and throttle body gaskets

- Checked butterfly valve/throttle shaft for proper motion and sticking concerns both before and after carb. removal and reinstallation - all seemed smooth and operating properly with respect to the governor. Note both governor side housing and carb. float bowl assembly were removed during reassembly and testing.

- Verified proper reassembly and mating of throttle shaft assembly to throttle body (matched up shaft notch to butterfly plate notch seat)

- Checked manifold bolts for any unusual looseness - all seemed OK - did not remove manifold or make a serious attempt to check for manifold leaks

- Checked choke for smooth operation - all OK

- Checked fuel flow to carb. (line only) and with float bowl assembly with needle valve and seat in place. Had what seemed to be good consistent flow on both accounts. Note fuel line has an inline filter installed and has run fine for years with this in place.

- Checked fuel flow with gas cap installed and loose - no difference in flow to carb. Both good.

- Checked governor area for obvious signs of damage - none found. Note governor spring seemed in good condition, although likely some governor parts have wear. Governor weights moved freely as did governor spring and rockshaft levers. I don't have too much experience with these, but understand the basic operation.

- Spark plug condition was checked. There was minor carbon buildup (nothing obviously unusual) and gap was .003Ē off at .028Ē. Gap was reset to .025Ē.

Other observations:

- OK, this may sound a bit odd, but both my Father and I recalled that when operating the throttle lever the idle position was always closest to the driver and full run was toward the front of the tractor, farthest position away from the driver. Whatís odd is that it seems to be the exact opposite from what I just described (lever close to driver = high throttle / lever away from driver = idle position) as confirmed by watching the throttle plate and governor linkage. This just seemed unusual, but maybe we are just not remembering correctly for some reason.

- Noticed slight abrasions on the float assemblies to the lower inside of each ballast (sticking float??). Bent each ballast slightly away (carefully at the tang!) from the abrasion site thinking that it would eliminate this possibility. Float seemed clear of any obstruction when placed in bowl in approximate proper position prior to re-assembly.

Work on the tractor will be somewhat weather dependant given the time of year hear (upstate NY), but Iíll do what I can. Iíll try to report back on any follow-up work, particularly if I get this resolved! Thanks in advance for any constructive advice or thoughts.

This post was edited by Sparetime at 15:49:06 11/22/09.


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