polaris sportsman misfiring

fish · Joined: 28 May 2007 Posts: 2

I have a polaris sportsman 500.I am having a problem with the engine skipping.It idles just fine.When you give it throttle it skips and backfires real bad.any suggestions?

srbjmw · Joined: 13 Mar 2006 Posts: 40

this may sound weird but check the throttle cable adjustment. i had a scrambler that backfired terrible ended up being the throttle cable adjustment. there is some kind of shut off switch.

fordguy · Joined: 06 Apr 2008 Posts: 3

Hi there, did this advice work? I have the idential problem and am having trouble narrowing it down. I've checked all the obvious and there is certainly nothing staring me in the face, i.e. spark plug, good gas, new air filter, muffler's not plugged, good compression. Problem is just as described, idles fine and runs great to about 1/3 throttle, then pops an backfires. Any suggestions?

4wheelsup · Joined: 17 Jan 2007 Posts: 73

have you serviced the carb and or injector it may be lean due to something pluged up or the choke out of adjustment

fordguy · Joined: 06 Apr 2008 Posts: 3

Ok, thought I'd let you folks know what I found. I read something in here about the throttle switches, well, I could only find the one in the throttle lever itself so I adjusted as I seen fit, no change. I pulled the carb off, fair amount of grit in bowl but no plugged jets, vacuum diaphram looked good. Pulled muffler off and tried running engine again, no change. (except I think I exceeded the "after 10:00 pm" noise rule in my town) Hooked up my neon plug wire to see if ignition was dropping when it started to pop, nice even spark even while backfiring, I'm starting to get the feeling at this point that it is mechanical. Pulled the valve cover and put dial indicator on exhaust valve, turned engine over and recorded .110" of vertical movement of exhaust valve. Moved over to Intake and found approx .350" of vertical movement. Realizing that these two readings should be somewhat close, pulled the cam out and found the center exhaust lobe completely wiped off of cam. Rocker that rides on it was smoked as well. Now, this part doesn't make sense to me, but the two intake lobes look like they have fifty miles on them. (this rig has 7500 miles on it) You'd think bad oil or bad oil pump or whatever the cause would have also affected the other lobes. By the way, there was oil all over everthing up there so I don't think that oil supply or pressure was the problem. Anyone have any ideas? Oh, and does anyone have a good used cam and rocker for a 1996 500 Sportsman? Good luck, eh mate!