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Farmall & IHC Tractors Discussion Forum
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39 M won't run smooth; HELP!!

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ih650

03-15-2006 20:19:21




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I have worked on tractors for almost 22 years and this has got me. The engine runs good wide open under load and idles fair. It runs terrible at part throttle idles poorly warm. I did a valve job and rerang the M&W high-dome pistons. I"ve tried 3 different carbs, 2 ignition systems and 2 intake manifolds. I pulled the front cover and checked the cam gear and key. It seems to miss and kind of lope just above idle to wide open. I am using Autolite plugs. Any ideas??

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BIG JOHN

03-16-2006 20:19:26




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 Re: 39 M won't run smooth; HELP!! in reply to ih650, 03-15-2006 20:19:21  
I know you said you changed manifolds a couple of times and carbs also. If you have a stud that the threads are not the best sometimes they just don't snug down tight. Take a propane torch, with the tractor running rough, turn on the torch but do NOT light it. Run it around the intake manifold and the block and the carb and the manifold. If it smooths out then you have found the problem or if not then you have for sure eliminated the leak idea.

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ih650

03-17-2006 19:30:16




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 Re: 39 M won't run smooth; HELP!! in reply to BIG JOHN, 03-16-2006 20:19:26  
John, I would have never thought of that. Thanks! It has a bad miss off of idle to wide open throttle. My next step is to try a super M head that I have.



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dej(JED)

03-16-2006 10:23:10




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 Re: 39 M won't run smooth; HELP!! in reply to ih650, 03-15-2006 20:19:21  
A 39 M won't run smoothly compared to a later model. Engine parts machining technologies were still primative on the early Farmall M's and H's.



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Janicholson

03-16-2006 06:31:02




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 Re: 39 M won't run smooth; HELP!! in reply to ih650, 03-15-2006 20:19:21  
Wayne has great ideas below,
I would ask if you replaced the distributor when "changing" ignitions. A worn set of bushings can act poorly at specific speeds, and not others.
A simple way to look at the issue is to hook up a timing light and aim at the front pulley (you are not looking for the timing mark, you are looking at any single mark or spot on the pulley to watch for lariations in timing). If the timing light shows the pulley to be rock steady when the tractor is acting up, try a different plug and look again. If this shows steady pulley location, I believe the distributor shaft to be ok. Distributor advance could still be an issue. check the springs and weights. Good luck, it is a complex problem.
JimN

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Wayne Swenson

03-15-2006 20:57:08




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 Re: 39 M won't run smooth; HELP!! in reply to ih650, 03-15-2006 20:19:21  
I think you need to check the governor-to-carburetor synchronization.
These adjustments are done with the engine off. 1. Loosen the 2 screws that are holding the governor tube to the governor housing & gently tap it so it "centers" itself then tighten the screws. 2. Remove the top cover on the governor housing (has the pipe going to the top of the engine) and check governor to carburetor synchronization. With the throttle lever set wide open, the clevis pin should just slip into the governor connecting rod that is in the tube. Adjust the clevis height if needed & lock the nut. You may need small fingers & a right angle needle nose pliers to make the job easier. Does the governor spring need replacing?
3. With the engine warm & running at wide open throttle (WOT), turn high speed mixture screw in until the engine begins to starve for fuel. Then turn the screw out until the engine begins to blubber. Now find the "sweet spot" in between the two settings. If you are working the engine (plowing, etc.), then the high speed screw needs to be turned out 1 turn or more beyond the "sweet spot" to be sure the engine isn"t starving for fuel and can develop its rated power.
4. The same procedure can be followed for idle mixture with the addition of the ldle stop screw to set the low speed RPM.
5. On the "M" carb, the idle mixture screw is an air adjusting screw so turning in will richen the mixture and out will lean the mixture.

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