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Discussion Starter #1
This 6X4 Gator is new to me. It has the Kawasaki 620D engine. Hours is not known but everything looks great. The problem is the rear spark plug fouls out after less than 10 hours of use. Three mechanics agree the spark plug is fouling from a too rich gasoline mixture NOT from oil. How can the rear spark plug foul out in less than 10 hours when the front spark plug looks new after 70 hours when both cylinders are fed by the same carb and the same intake manifold? Compression on both cylinders is 180 PSI. The two coils have been swapped with no change. New valve seals have been installed.. The engine uses No oil. The engine does not smoke. The engine starts right up when cold or hot. The engine makes great power. The engine sounds perfect when running until the rear spark fouls and kills the spark. Any ideas will be appreciated.

Thanks........
 

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Is it oil fouling the rear plug? Like valve stem seal leaking?

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Discussion Starter #3
The rear plug is fouling after 10 hours from too much gas. It is not fouled from oil. Compression is 180. Valve stem seals were placed. Engine starts quickly cold or hot. Engine runs great. Engine has great power. Engine does not smoke. Engine does not use any oil. The front plug looks new after 70+ hours of running.
 

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I'd have to guess something with the intake, an external problem could be located with spraying carb cleaner around it when running and note any change in rpm's, internal possible carbon build up not allowing a clean flow.
 

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Discussion Starter #5
Thanks - My next project is to remove the carb and intake manifold to look at carbon or "critters". Since the muffler has two intake pipes and just one exhaust pipe, anybody heard that only one part of the muffler is clogged - the part of the muffler that feeds the rear cylinder? I guess anything is possible at this point in time
 

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Is it possible to swap coils/spark wires in this unit? I'd make certain you don't have a weak spark in the cylinder that is becoming fouled. Good spark at idle doesn't mean there is good spark under load... I'd even swap out the plugs as part of the testing sequence.
 

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Discussion Starter #7
Update - Today I borrowed a true John Deere factory service manual on this Gator. First I removed the carb and intake from the engine. The intake had some crud and what looked like carbon. I also think the previously owner used ethanol gas. The Gator is 18 years old. I cleaned the intake and all the crud came out. Then I inspected the carb. I used carb cleaner and compressed air and cleaned the carb best as I could without tearing it apart. I did not have a rebuild kit.

After reinstalling the carb and the intake on the engine I decided to go through the 3 page instruction in the service manual to adjust the mixture and to adjust the carb in general. The first step was to turn the mixture screw all the way in to the stop and then turn the screw out 3/4 of a turn. 3/4 of a turn "out" was the base line to startt to adjust the carb. The mixture screw on this carb had a plastic limiter cap on it. After removing the limiter cap I started turning the screw to the stop. It took more than 5 turns to get the mixture screw turned all the way "in". Then I turned the mixture screw 3/4 of a turn "out" as stated in the service manual. Then the service stated to turn the key. The engine started right up and ran smoothly.

Then I followed the 3 pages in the service manual to adjust the mixture, the idle and high RPM limit, the operation of carb in general etc. The "sweet spot" on the mixture screw was between 3/4 and 1 turn "out". Remember I found the mixture screw was originally turned more than 5 turns "out" and had a plastic limiter cap on it so I could not turn the screw more than 1/2 of a turn nor could I determine how many turns the mixture screw was turned "out" until I removed the plastic limiter cap..

I installed new spark plugs and I drove the Gator 3.2 hours around my farm. When I got back home I removed the rear spark plug. It looks brand new. Ditto for the front plug. Before I adjusted the carb and cleaned the intake the rear plug would be completely sooted over with black carbon after less than 3.2 hours. I think I found the problem.

I know 3.2 hours is not a full test, but I think I found the problem. Originally when I bought the Gator he mixture was WAY too rich. Why it only fouled the rear plug is still a mystery.

I will report back after I put 20-30 hours on the Gator. I think the rear plug will look just fine after 30 hours. I hope the mystery is solved.

Thanks for all the ideas.
 

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Discussion Starter #8
PS: Yes I swapped the two coils. That did not make any difference. That was one of the first things I tried.
 

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Discussion Starter #9
After several months of work on my "new to me" 2002 vintage 6X4 Gator I thought I should post an update. Thanks for all the posts that helped me.

The rear spark plug fouled out after no more than 6-10 hours of use. The fouling on the rear plug did not look like oil fouling. It looks like fuel fouling. The front spark plug looked new after 100+ hours.

I replaced valve seals, swapped the two coils, checked the muffler for something stuck in it, cleaned the carb and installed a "kit" in it, compession is 180, uses no oil, exhaust is "clear" and no blue or black smoke.

Finally I bought a service kit from John Deere. The kit has 2 qts of oil, oil filter, fuel filter, air filter, and two new NGK spark plugs. I noticed the spark plugs in the John Deere kit were NGK heat range 2 which are" hot" plugs. When I bought the used Gator it has new NGK heat range 5 plugs which are very "cold" plugs. When the rear plug fouled in less than 10 hours, I bought NGK-5 plugs from the NAPA store and the fouling continued.

After installing the "hot" NGK heat range 2 plugs that came in the John Deere service kit, the rear NGK heat range 2 spark plug has been in use for 53 hours with no fouling. I removed the rear spark plug today to inspect it and it looks as new. I still wonder why only the rear spark plug fouled with the "cold" skark plug while the front spark plug did not foul.

Regardless as soon as I realized that my Gator was supposed to use NGK range 2 (hot) spark plugs, my problem went away.
 

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Thanks for reporting your findings.

Glad it wasn’t anything too serious.
 

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After several months of work on my "new to me" 2002 vintage 6X4 Gator I thought I should post an update. Thanks for all the posts that helped me.

The rear spark plug fouled out after no more than 6-10 hours of use. The fouling on the rear plug did not look like oil fouling. It looks like fuel fouling. The front spark plug looked new after 100+ hours.

I replaced valve seals, swapped the two coils, checked the muffler for something stuck in it, cleaned the carb and installed a "kit" in it, compession is 180, uses no oil, exhaust is "clear" and no blue or black smoke.

Finally I bought a service kit from John Deere. The kit has 2 qts of oil, oil filter, fuel filter, air filter, and two new NGK spark plugs. I noticed the spark plugs in the John Deere kit were NGK heat range 2 which are" hot" plugs. When I bought the used Gator it has new NGK heat range 5 plugs which are very "cold" plugs. When the rear plug fouled in less than 10 hours, I bought NGK-5 plugs from the NAPA store and the fouling continued.

After installing the "hot" NGK heat range 2 plugs that came in the John Deere service kit, the rear NGK heat range 2 spark plug has been in use for 53 hours with no fouling. I removed the rear spark plug today to inspect it and it looks as new. I still wonder why only the rear spark plug fouled with the "cold" skark plug while the front spark plug did not foul.

Regardless as soon as I realized that my Gator was supposed to use NGK range 2 (hot) spark plugs, my problem went away.
Do you remember the spark plug number? I am having the same issue.
 
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