I have a 1996 Polaris Magnum 425 2x4, it pops and backfires at idle, have clean carb and changed out fuel pump, any ideas? Also how do you adjust valves?( intake and exhaust)

 

Welcome to the forum!The cam may have a flattened or ground down exhaust lobe! Sounds like it from you description! Just pull the valve cover,pull recoil slowly and look at the center exhaust lobe to see if its elliptical like the intake lobes on each end of the cam OR ground down.
Common problem on early 425 and 500 engines!(1996-2000) Engine would just pop back,sputter,no power! If the lobe is ok, then check when the cam sprocket index pin(locating pin) is straight up,then its at TDC and the valve clearance can be checked. .006 intake and exhaust! OPT

 

Thank you for your help, will try your advice. Will let you know what happens. Also how do you check the timming on it. Mike

 

You can pull the 14 mm plug at the top of the recoil housing and also the square plate covering the cam sprocket. Pull the recoil slowly(easier to have spark plug out) until intake rocker arms go down and start to come up. As the cam sprocket index pin moves toward the top of the head,look in the recoil housing and first you will see the "F"(fire mark) and the the "T"(TDC) line etched into the flywheel. Sometimes hard to see. The TDC mark on the flywheel lines up with the pointer on the recoil housing,at the same time the cam sprocket index pin should be directly center of the head.(This is where you are able to adjust/check the valve clearance) Timing is never a problem unless the lower crank sprocket key breaks or the chain has excessive slack and might jump a tooth! OPT

 

Thanks again, going to try and get to it this weekend. Will give an update next week.

 

Made all repairs, runs little better. Now I have a inline coil wire tester and at low idle does not have a steady spark, but can crack throttle runs fine and has a steady spark. Sounds like it might be an electroic problem. Thank you for any advice, Mike

 

What repairs were made? Inline coil wire "checkers" not an accurate way of testing ignition system . Pull recoil housing, check if any dirt/trash around flywheel and pick up(trigger) coil. Resistance specs on the pick up coil is around 97 ohms on the white to white/red wire coming from the stator that plugs into the cdi. Should be around 440-446 ohms on the green to black stator wires that plug into cdi also. Close as I can remember on the stator specs. Check these out,plus check if any breaks,worn spots on the plug wire from coil to the plug cap, plus plug cap should be close to 5K ohms resistance.Plus check all connections under the front panel along with the grounds (brown wires) where they mount at the coil to make sure they are tight. OPT

 

I had a 325 Magnum that had the wire harness from the stator/pickup coil rub through on the fins on the jug and it just happened to rub through the wire that goes to the CDI from the pickup coil. It would run fine for awhile, then act like you describe yours, pop, backfire, no power. Drag it home, then it would start fine and might run the next 4 or 5 times we used it, then it finally got to where it did it all the time and I found the problem.

 

We talked awhile back, about 96 425 Polaris Magnum, for skipping and back firing. I have removed,clean carb., check and set values, check timming, checked all brown wires and ground wires, check ohms for pick up coil and had 98 ohms, checked green and black wire for stator and had 0 ohms. Check green to red on stator had 4.6 ohms, could this be part of my problem? Also pulled recoil housing, there is no dirt or trash in housing, it is clean.

 

If green and black zero out,then stator charge coil possibly bad! Can cause it to run bad OR not at all! As far as I can remember without a manual,should be around 440 ohms! PLUS did you look carefully at the exhaust cam lobe when you checked the valves?? OPT