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Discussion Starter #1
First of all let me welcome myself! I have been a long time lurker.

I have a 96 sportsman 500 (as if the title didnt tell you that) that is cutting out under load (sometimes).

Repair history is as follows.

Quad was torn completley down for a frame up rebuild, and this problem did occur before tear down. All new fuel system componets. Fuel stems in tank, lines, fuel pump, selector valve, and filter. The carb was torn down, soaked and rebuilt with new jets etc. Float was adjusted (twice). New plug also.

In the begining, I thought that it was starving for fuel when it was cutting out on its top end. However after some careful consideration, testing and thought, I am leaning more towards an ignition problem. It is an intermitant problem, that doesnt happen all the time. Can be anyware from 1/4 to WOT and when it is loaded, hill, pushing snow, etc it begins to backfire and pop.

There is no exhuast restriction, and the ETC switch has been checked and re-checked.

The plug is comming out like it is running a little rich, and when I have another person ride the quad, and make it stumble it does puff some nice carbon out of the exhuast. A compression test was done, as well as a CLD test. The readings are not perfect, but acceptable for a 14 year old engine.

I have tested the coil, and the readings are off, but not by a long shot.
Same goes with the rest of the ignition system.


Thoughts?
 

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First off, welcome to the board!
 

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fuel pump or fuel filter ?
 

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Discussion Starter #4
*Update*
Solution found, and problem repaired.
I have read many posts in this forum regarding the same problem, so I figured I would post a plausible solution.

After having every symptom of running lean, I realized that it was not, and it was in fact running with the correct air fuel ratio, just not enough spark to ignite the fuel.
Story goes; I threw everything at the fuel system you could imagine, including a brand new carburetor. With little to no results, still intermittent high rpm, and low rpm high load cut-out. I began to suspect ignition. While following the Clymer manual coil test procedures, the picture shows to test the coil’s secondary side without the spark plug boot on. With the boot on, coil was 1.4M Ohms, damn near open in my book. Without the boot, 6.3K ohms, just as the book says it should be.
I went ahead and ordered a new coil, with included wire and boot from eBay. Once received, the whole shabang, coil, wire and boot tested to 6.3K on the secondary side. Perfect!
I decided to cut apart the old boot and section cut the inner works to see what the problem was. There is a small wound wire (looks like a spring) that was very brittle, and was the source of the super high resistance in the ignition system.

Moral of the story. Super high resistance in the ignition system (sometimes, depending on temperature) causing a weak spark. Weak spark is not able to keep up with engine load, and causes high rpm cut out, and stumble under load. Head pipe glowing red due to un burnt fuel in system due to weak spark. Running better when air box lid is off, due to leaner mixture. Easier for weak spark to ignite.

I’m sure this won’t be the root of everybody’s problems, but mine runs like new, even pulls wheelies with ease again, with a 39 dollar eBay coil.
 

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*Update*
Solution found, and problem repaired.
I have read many posts in this forum regarding the same problem, so I figured I would post a plausible solution.

After having every symptom of running lean, I realized that it was not, and it was in fact running with the correct air fuel ratio, just not enough spark to ignite the fuel.
Story goes; I threw everything at the fuel system you could imagine, including a brand new carburetor. With little to no results, still intermittent high rpm, and low rpm high load cut-out. I began to suspect ignition. While following the Clymer manual coil test procedures, the picture shows to test the coil’s secondary side without the spark plug boot on. With the boot on, coil was 1.4M Ohms, damn near open in my book. Without the boot, 6.3K ohms, just as the book says it should be.
I went ahead and ordered a new coil, with included wire and boot from eBay. Once received, the whole shabang, coil, wire and boot tested to 6.3K on the secondary side. Perfect!
I decided to cut apart the old boot and section cut the inner works to see what the problem was. There is a small wound wire (looks like a spring) that was very brittle, and was the source of the super high resistance in the ignition system.

Moral of the story. Super high resistance in the ignition system (sometimes, depending on temperature) causing a weak spark. Weak spark is not able to keep up with engine load, and causes high rpm cut out, and stumble under load. Head pipe glowing red due to un burnt fuel in system due to weak spark. Running better when air box lid is off, due to leaner mixture. Easier for weak spark to ignite.

I’m sure this won’t be the root of everybody’s problems, but mine runs like new, even pulls wheelies with ease again, with a 39 dollar eBay coil.
thanks for the info, makes good read
 

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I am having a very similiar issue, now I have a better idea of where to check. Did you check to see you your spark looked beforre and after the repair??

Thanks

Robert
 
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