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Rough Running B

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Kelly

10-29-2001 12:50:16




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I've got a 38 B that doesn't want to run smoothly no matter what I do. It's got a professionally rebuilt mag and carb, the engine is rebuilt, no airleaks around the manifold, timing is perfect, starts easily, idles down low, but still spits and sputters at all RPM's. If you put it under load, it smoothes out and runs perfect.

I just got my 44 B running and I've never seen a two-cylinder run so smooth - you'd think it was a four-cylinder,(perish the thought!)

A couple of guys much more knowledgable than I have told me that the 38 B runs OK and that's as good as it's going to get. I've seen and heard plenty of other B's of that same year run a lot smoother.

I'd like a second opinion. (If you have chest pains and the doctor tells you that you're fine, then..... ..)

I'm out of ideas and appreciate yours.

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Fred-CT

10-30-2001 19:17:39




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 Re: Rough Running B in reply to Kelly, 10-29-2001 12:50:16  
Kelly, something out of left field - is the clutch drive disc installed in the proper position (and the flywheel for that matter)? I just went through this with my "A" and it made a big difference in how smooth it ran. Good luck!!



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Kenny

10-30-2001 08:42:57




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 Re: Rough Running B in reply to Kelly, 10-29-2001 12:50:16  
Problem could be several different things, I had the same problem once with a later model and I pulled my hair out, but when I finally fixed it it was as simple as changing plug wires as someone had put new automotive wires on it and that will not work properly. Check wires and plugs and then be sure that the valves are properly adjusted, and if that don't fix it then it will most likely be a cam or govenor problem.

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geoff

10-30-2001 08:03:54




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 Re: Rough Running B in reply to Kelly, 10-29-2001 12:50:16  
It's running rough because it only has 2-cylinders.

Just kidding!
I don't have anything against John Deere.



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KWB

10-29-2001 17:44:04




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 Re: Rough Running B in reply to Kelly, 10-29-2001 12:50:16  
An excellent post by Clooney, sure would be nice to have him in the neighborhood. I would like to add one thing. I smoothed the idle out some on my 40 B by switching to champion W89D plugs. These are a deep hot plug and seem to be able to light off things a bit better. Worth a try.



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Kelly

10-29-2001 17:48:29




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 Re: Re: Rough Running B in reply to KWB, 10-29-2001 17:44:04  
I'm running the Autolite 386's in it now. Would the Champion's be better than these?



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KWB

10-30-2001 16:18:46




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 Re: Re: Re: Rough Running B in reply to Kelly, 10-29-2001 17:48:29  
I can't answer that question without being able to compare both plugs, but the idea is to get the spark as deep into the combustion chamber as possible.



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Clooney

10-29-2001 14:37:18




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 Re: Rough Running B in reply to Kelly, 10-29-2001 12:50:16  
Kelly, that uneven running at no load is part of the 2 cylinder history. Some are worse than others & can be aggravating to improve. Things I have found over the years that effect the uneven running are: (worn camshaft, quite common on older high hour J.D.s), (worn valve guides), (worn magneto bushings), (worn cam gear to governor gears, effects running timing), (worn throttle plate in the carb, common & really effects low speed operation), (worn throttle shaft bushings, effects low & no load operation), (carburetor type & idle fuel hole size & cleanliness, all-fuel carbs are worse because they are designed to meter thicker fuel, idle fuel hole size due to rust & improper use of a drill bit to clean them, especially critical if the idle needle needs to be set different for idle/mid-range/off-idle operation), (ignition timing, sometimes a little less running timing will make the engine work harder & smooth it out some), (plugged or plugging air cleaner wire mesh, try running without air cleaner installed), (worn throttle linkage pivots & worn hole in carb throttle arm), (leaking float bowl gasket, causes part throttle metering problem), (plugged or plugging carb vent, causes metering problem & carb siphoning), (probably a lot more but that is all I have for now)..... Is it actually running poorly with no load or does it just sound bad? If it has a Wico C or X mag the spark plug fires every time the piston comes to TDC & will sometimes pop in the exhaust if there is un-burnt fuel that ignites with the spark on an open exhaust valve.....The best way I have found to try to isolate the uneven running is to try different parts, & seeing as you have a 44 B that runs good that would make a good donor to swap the carb & mag from. If you are running an open pipe instead of a muffler try a muffler also as that helps even out the errant pops. Remember, that just because a carb, mag or other device is rebuilt by a "professional" DOESN'T necessarily make it right, so don't assume it CAN'T be the problem

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Kelly

10-29-2001 17:44:27




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 Re: Re: Rough Running B in reply to Clooney, 10-29-2001 14:37:18  
I tried another rebuilt carb right out of the box and it ran exactly the same. Also the same results with another freshly rebuilt Wico X. The head's been rebuilt with new valve guides and seats. It's got a new muffler and the air cleaner is clear. Another guy rebuilt the engine and he said the cam was in good shape. He got into the governor and replaced a bearing and had to replace one of the bevel gears (the one on the fan shaft), and now the governor howls a little. I'm convinced the mag and carb are OK, and that it's something else causing the rough running. I don't have the experience or trained ear to pinpoint the problem and need someone like you to hear it run. Going to be in the OKC area anytime soon?

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Clooney

10-29-2001 18:48:44




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 Re: Re: Re: Rough Running B in reply to Kelly, 10-29-2001 17:44:27  
Kelly, just looking at the cam with out actually measuring the lobe lift, opening & closing profile is just a guess at best. I have worked with many old J.D. cams & unless the cam is worn with flat spots or the ends of the lobe are flattened out I have to measure the profile to determine if it is serviceable or not..... ..Try varying the ignition timing a little in each direction to see if that helps your problem..... ..... ..The other thing to keep in mind on a single induction J.D. 2 cylinder is due to the 180/540* firing order the L/H cylinder gets most of the fuel/air mixture at low throttle openings (the L/H cylinder fires then 180* later the R/H cylinder fires, then the engine coasts for 540* at which time the intake manifold fills with a full load of fuel/air, the L/H cylinder uses most of that & the R/H cylinder only gets what's left). At higher throttle openings there is more fuel/air available for both cylinders & the R/H gets a bigger share). That is why the old single induction 2 cylinders run much better under load, because the throttle plate is open farther & more fuel/air is flowing.

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