Hello, Im new here and Just bought a used 1995 Polaris Magnum 4x4. It starts and runs good but when ever you goto rev it up it backfires and sputters. It will never rev wide open, I checked the plug it looks like new also cleaned the carb and made sure its getting plenty of fuel. Im puzzled cause it idles great?? Any ideas? EJ

 

Hold the override button in and see what it does.Make sure the muffler isnt stopped up.Let us know.

 

Hello, thanks for the reply, just tried holding the override button and its still acting the same, idles good but acts like its lugging and starts backfiring when you start giving it throttle. Check the exhaust also its not plugged up. Anymore ideas please let me know. EJ

 

Hate to say but it sounds like a bad cam.Take the valve cover off and check the valve settings should be .004 on both int and ext while there inspect the cam for wear.These motors are known for eating cams if the oil isnt changed enough.

 

EJ dose it have a rubber boot between the carb and the head.If it dose take it off and look real close for any splits in the rubber...

 

sorry told you wrong on the settings its .006 the .004 was for our old Breeze.

 

First thing that comes to mind is the camshaft, but, those older Magnums were also known for the Reverse Limiter to go out (acts as if it is in revers all the time, override button will not affect it) - if the camshaft checks out OK, then try bypassing the reverse limiter. Remove the plastic around the fuel tank to expose the wiring panel. Find the Reverse Limiter (black rectangular box in front of the steering shaft) and unplug the black?? wire (I think it was the black - and don't have my book handy) coming from the limiter to the panel.

Just remember that bypassing the Reverse limiter will allow the bike to go as fast in reverse as it will in forward.

 

Thanks for the replys! I just checked the reverse limiter and it seems to work fine, it runs faster with the buttom pushed in also unhooked the black wire and no difference going forward. I will pull the valve cover next and check that out. How much compression should this motor have? Also anyone rebuild a 425cc? I rebuilt a couple truck engines but this thing looks abit hard to get at. EJ

 

100+ PSI on compression

 

Hey, Good call on the camshaft Looks like its the problem, I have pic of it if I knew how to post it. Also I check the compression before tearing it apart and it showed 115 psi. Should I tear it on down and give it a ring job while im this far in? EJ