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K321 High Rpm Misfire Fixed


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#1 Clippnalawn OFFLINE  

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Posted May 06, 2013 - 07:48 PM

I have a jd 140 that had been giving me some issues at high rpm, it would pop and miss fire at high rpm. Some days seemed worse than others and it was driving me nuts! I started with new points, set the gap, plug was pretty new, new plug wire, new coil/points wire, readjusted the carburetor(had readjusted the carb numerous times and it would improve just not to my standards), swapped the condenser with a good used one and still missing and popping....

So I put the adjustable spark tester on it, ran it until it was good and hot then full throttle. The engine was running terrible but the the spark looked great.... Assuming it must be a carb issue I started looking for intake leaks etc, finally found that the choke was closing just the tiniest bit(looks fully open from first glance). If I hold the choke all the way open she runs like a champ!!
Not sure if the detent ball in the choke shaft isn't holding it open or if the cable is pulling on it. I tried adjusting the cable a few times but it still pulls closed a little bit with the vibration. I think the next step is tightening up the choke lever...maybe that will help hold fully open..
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#2 IlovemyCub OFFLINE  

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Posted May 06, 2013 - 07:55 PM

Interesting how a little problem can cause a big mess! My Cub Cadet 122 would backfire and stuff, and I replaced the points and condenser, re-built the carb, and a lot more! But, it ended up being the main needle off just a hair. now she runs very smooth and well. Glad you fixed the problem. Good luck with her. Ian  


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#3 superaben OFFLINE  

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Posted May 06, 2013 - 08:02 PM

Kohlers are very picky about their choke.  That was a good diagnosis you did on a very tricky problem.

 

Ben W.


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#4 lyall ONLINE  

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Posted May 06, 2013 - 09:49 PM

have you checked the push rod for the points?

It could be worn and it might be sticking a little

 

have you checked the gap for the valves lately?


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#5 Clippnalawn OFFLINE  

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Posted May 07, 2013 - 12:07 AM

have you checked the push rod for the points?
It could be worn and it might be sticking a little
 
have you checked the gap for the valves lately?


When I replaced the points I looked at the push rod, it had a small ridge so I rubbed it down with scotch brite, I didn't measure the length though. The valves have been adjusted within the last 20 hours of use(when I flattened the head and installed a new head gasket).

It's funny how there are so many little things that can affect the operation...but if its all in tip top shape they sure do run good!
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#6 JDBrian OFFLINE  

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Posted May 07, 2013 - 04:58 AM

Thanks for that tip. I'll have a close look at my 314 and see if it's doing the same thing. i get an occasional stutter at high speed. In my case it could also be the throttle bushing on the carb which has a bit of slack in it.


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