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Steve Howard

1997 Polaris Magnum 425 4X4 back firing through the carburetor

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Ran find shut down the quad next day would start and idle when you try to accelerate it would start popping through the carb got a rebuild kit soaked it in chem clean after break down for 12 hours on slow vibrate reassembled and adjusted per manual still the same thing any help would be really appreciated thanks and happy ridding  

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Only other thing I can think of is the throttle controller.  Are there two wires coming from that throttle ?  You would have to take the two screws off of the top of the throttle on the handle bars and see.  

I think that bike is to early to have the rev limiter on it but let me know.   

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On the throttle in the handlebars ? If so open it up and see what’s going on with the wires. I believe it’s a normally open circuit. It may be bad.  There is a plastic partition that separates the two contacts.   Sometimes that falls apart or water is inside the throttle compartment.  Separate the wires or disconnect them and see how it runs.  

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I took the cover off everything is clean and dry? I disconnected the wires from the throttle lever and still the same starts right up but wont accelerate  

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Ok good so that eliminates that.  I think your next move is back to the fuel.  I know you soaked/vibrated the carburetor good but sometimes the clogs are not as easy as soaking and if something got wedged in like a small piece of dirt or rust.    You may want to take that carb off and take a pice of wire and clean all the jets and ports out good.  I like to take a piece of brake cable from a bike and separate the strands and use one of the strands. It fits right in the little holes. Blow it out with air and re assemble.   

Make sure the float is good and set right and not closing to early.

Double check the gas petcock on the tank and make sure it’s clear and free flowing.  

This will eliminate any fuel delivery problems or questions. Put a fresh plug in and see what happens. 

If this clears it up great  if not you have to start looking at spark issues  or a breakdown in the ignition system. 

Double check that your kill switch is not faulty and shorting or a loose contact or full of water.  

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You can double check the wiring all the way back to see if there is a bust in the wires. 

Have you tested the spark for any breakdown.   I purchased an in line spark tester after another member pointed  me in the direction of the rev limiter and found my spark was breaking down due to the rev limiter having a fault but my problem was in the handlebars at the throttle.  I separated the wires and it ran fine.

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I bought a inline spark tester and checked the quad not loosing spark I can hod my hand lightly over the carburetor and I can get it up to about a 1/4 throttle and it starts popping through the carb real bad Thanks 

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Have you checked the boot connecting the carburetor to the engine for any cracks or leaks ? If you have good spark then I’m leaning toward a fuel problem.   It’s sounds like you did the right job on the carburetor but covering the intake starving the engine for air allows it to rev then it appears it’s within the carburetor. Is that bike gravity fed from the gas tank or a fuel pump ? 

 

The only other item I can take a guess at is the gap between the flywheel and pick up coil.  Take a look and see if that gap is within speck.  Double check the pick up coil is tight and all is ok inside that cover.   

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Get a can of carb cleaner. As you give it gas, give it a little shot of carb cleaner through the intake hole and see this extra fuel makes it rev. If it does, then you know you have a fuel starvation problem.

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Welcome back

I don't think it would be the cam, maybe its time to start going over the testable electrical parts. Regulator, stator coil and pick up coil.  
If you have the manual its stated what the readings should be as well as the process. We can also help you along, its not hard to do and all you need is a multi meter.  

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Absolutely could be a cam problem. Polaris had big problems with cams wearing out in short order back then. They fixed the problem I think in 2001. But do the test I mentioned above first and report back the results.

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I would agree with @BuggyMasters if it was a problem that slowly got worse. BUT for the atv to be running fine one day and the next day have this problem?  Polaris did have a cam issue but it showed up over time, not over night.  Spark plugs started to foul and the backfiring once in a while.   I just don't see it happening over night.  

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Hey just wanted to get back with everyone on the Magnum I finally got time to work on it again this weekend I pulled the valve cover and rocker arms to find the exhaust lobe on the cam was worn all the way down replaced cam and exhaust rocker arm put back together and runs great I want to thank everybody for the input  

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