Hello,

I am working on a 500 sportsman and it will start right up and backfire through carb when you give it some gas. I have changed spark plugs, Set valves to 6 thousands, cleaned carb, tried different settings with needle, it is set on the top slot so it should be running lean, dropped it down no difference, tried running with and without air cleaner, cleaned all the contacts in the throttle housing and the other side, there is no air leak at carb boot, I have cleaned the carb numerous times, i am at a loss as what could be wrong with it, it has 2600 hundred miles on it, any help out here

Thanks in advance

 

Any help out here?

 

Does it only backfire out of the carb or does it rev up as well? Does it act like the rev limiter might be acting up? Is this your quad and have you owned it for a while? Could the flywheel key be sheered so the timing is off? How did the cam look when you adjusted the valves?

 

Thanks for responding,

No it is not my machine, I am working on it for someone else and am waiting for a manual for it. This is the first Polaris I have workrd on. I did a couple of things the last 2 days to it. It was backfiring out of the carb when trying to rev it up. I moved the jet needle clip to the 2nd position from the top, It was on the bottom of the needle. It will rev up now with very little backfire but it still does it. If I put the machine in reverse it will backfire like crazy. I took apart two switches on the transmission and cleaned them and sprayed them with wd-40. So I am assuming it has something to do with a switch somewhere. As far as the cam goes it had some wear on it but the cam lobes are there and not worn off like i have heard from others about this. The valves were way off before I set them like 008 intake and 011 exaust so the machine probably never had the valves set in its life. 2600 miles on it. It is running better but the problem still exists. For the heck of it I ordered a new main jet and neddle. The cam chain and everything there seems to be in good shape, Maybe it slipped but I do not think so right now ,I will check timing as soon as I get a book. Thanks in advance for your help

 

Ok first off , the backfire while in reverse is normal .That is the speed limiter for reverse that kicks in at about 3000 rpm.To make that stop push the OVERRIDE button Warning it will go full throttle now in reverse it also activates 4 wheel drive for reverse gear.
Needle and seat is always a good change.
I would check coil and wires at night to see if any sparking or arching.
possible cracked coil.
From there update you should fix it with the needle and seat

 

Thanks for reply, I will wait for parts and in the meantime will check coil.

 

Check to see if the exhaust valve is opening all the way, and at the proper time. Because if it is not it could be the build up of exhaust poping out of the carb.