havent had it running for a few years changed cdi box, stator ,regulator got it running after unplugging reverse override switch. went for three short rides ran great went for a four mile ride exhaust pipe got hot figured muffler was plugged shut it off three times while on this trip started up everytime loaded it back up went home when i got home went to start it turns over but wont start.checked and have spark checked and have gas .gave it a shot of ether backfired took off exhaust pipe still backfires and wont start up no idea what could have happened after i shut it off.

 

I have that same problem,backfiring through both ends.. sounds like a common problem on these early 500 engines. Sounds like a flattened exhaust cam lobe. Pull the cam cover and see if the lobe is ground down. See if it looks like this cam a member posted on his Scrambler 500.Bad Cam Pic - ATVConnection.com ATV Enthusiast Community If a cam is needed always replace the exhaust rocker arm also. Plenty of aftermarket ones on ebay now. http://www.ebay.com/itm/POLARIS-SPOR...0a5f81&vxp=mtr

 

thanx for the quick response opt i do recall the engine backfiring the last time i started it before i rode it the last mile and a half would that cam go that fast what i mean is ,it was running so good before that when i loaded it it was idling fine when i shut it off.

 

They can do some strange things. They can run ok,then seem like all of a sudden problems start happening,but actually they can wear down gradually over time and then start back firing,will idle ok,but wont take throttle. This may or may not be the problem,it may be something else such as stopped up fuel filter,carb problems,a bad fuel pump,but with all the cams that did this,I'd check this out first and go from there.

 

hi opt if i take the top cover off do i just pull the rocker arm off to observe the cam? i see they do not sell gaskets with the cam, can you reuse the old one? also when i took the carb. apart, the plastic washer that holds the diaphram down would not stay down on the one side i glued it down. i suppose that could have let go. i had also bypassed the fuel pump as it was hardly pumping gas out, would you reccomend hooking it back up it seemed to run ok without it?

 

You can reuse the cam cover gasket. You don't have to remove the rocker arm to check the cam lobe. It's pretty evident if it's ground down when you compare it to both intake lobes. Don't glue anything down in the carb! Look at this carb break down.Order any parts if needed.Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse Plus bypassing the fuel pump may not allow enough fuel to reach the carb. Order a cheap new one.This alone could be causing problems.http://www.ebay.com/itm/Fuel-Pump-For-Polaris-Sportsman-400-500-600-Magnum-325-Outlaw-450-Predator-ATV-/181568842571?hash=item2a4658ab4b&vxp=mtr

 

after our last talk opt i went ouy in the garage to check a few things i hit the starter button she turned over and then started free wheeling i took a small hose slid down the spark plug hole pulled it over by hand [recoil rope] could not feel piston moving . i am thinking connecting rod what do you think? any thought as to why this would happen ? again thanks for your time and input i really appreciate it . dave

 

Using a small hose or straw down the plug hole and slowly pulling the recoil and piston isn't moving it up? Then that doesn't sound too good.. Might be time to invest in a good service manual.. Don't think I've ever had a 500 break a rod,but who knows.. P.S. pull the recoil housing and see if the flywheel has sheared a key. If it has this may be the problem if it's sheared bad enough to where the flywheel is just spinning on the crank shaft.

 

i took your advice and pulled recoil and sure enough the key was broke now i am wondering if that is why it wouldnt start . key was already breaking .your knowledge is irreplaceable im up here in wisconsin and its the big push to get jobs done before winter so i have been working dawn to dark so havent had much time to look at 4 wheeler it is truly wonderful to have a person like you that is willing to share your knowledge i am sure i will be talking to you again and thank you for your help i owe you. dave

 

500s were the worst on shearing flywheel keys. That in itself is probably the reason for the backfiring and no start as it probably jumped ignition timing. Takes a 5 mm woodruff key.Look over the flywheel carefully to make sure the key slot isn't wallowed out.3081447 KEY $5.68