So I have had a weekend of fighting Polaris. I have a 2008 500 that when it came to me to would not run so I checked fuel flow and it was pumping fuel to the carb at a steady rate so I pulled it a rebuilt and cleaned the carb. Then it would start but it was hard to start and popping out the intake. So checked the timing, Cam lobes and adjusted the valves. Now it will start and run and idle then die then it will start and cut out cough and pop back through the intake. Then it will be very hard to start and then repeat one of the above. It is not constant. The only thing I have not checked on this is the flywheel key. Any thoughts of what else to check? Thanks in advance.

 

Busy beaver today!! Check that you have good spark first.Check the flywheel key,plus behind the stator is the slotted nut that holds the lower cam sprocket in place. You can see if it's backed off. If it has,the sprocket can shear it's woodruff key and jump timing a tad enough to cause problems also. Seems like the Sportsman 500 was the main one on shearing woodruff keys.

 

It was the flywheel and key. It rolled the key and now the grove in the flywheel is about double what it should be. So while I was in there I went ahead and looked at the cam gear the nut was loose almost spun off and the key was just starting to get a grove in it. So how do I tighten that nut and keep it in place. I can not believe it does not have a locking tab on it. Is there anything else I should replace while I am in there? I am going to put in both keys and the flywheel. The bike only has 300 hours on it.

Thanks

 

Mine was hard to start with a back fire , turned out the pulse coil's magnetic face was dirty with metal filings stuck to it . Once it was cleaned up everything was fine again.

 

This was the key is was almost cut in half and the flywheel slot for the key is almost double width now. Not going to be a cheap fix but got to pay to play.

 

Had this happen several times also along with the crank sprocket key way splits on the 500. Had a good local machine shop buildup the flywheel key slot and cut down to proper size. Like I mentioned the 500 was the worst on this happening. On the slotted nut use red locktite and stake this nut down tight with a punch if you don't have a slotted nut socket this size. Shouldn't have anymore problems after this. Even though the nut is reverse threads and shouldn't back off,they do. Plus You'll notice that from the factory Fugi doesn't use locktite on these threads.

 

OPT, I have a 2006 Sportsman 500 HO and a 2002 Magnum 500. Does this problem apply to these machines also?

 

Any 500 engine can have this happen no matter what year or model it's in. Never had one happen in the Magnum 500 just the Sportsman 500s,but that could be because we sold so many Sportsmans versus any other model.But the engines are the same. Like I mention you wouldn't think the slotted nut could back off also since it had reverse threads and force to keep the nut tightened was on it as the engine ran,but they did back off. When that happened I just used red Loctite on the threads and tightened the nut. Possible when the flywheel keys shear and the engine back fires,enough rearward force can cause this to happen,but I've also had slotted nuts back off and flywheel keys were still intact and the flywheel nuts were tight.. Strange engines.

 

Ok So I got a new used flywheel and new keys for both the cam gear and the flywheel. Put it all back together and it will start every time but it is popping out the carb. Not as bad as it was but it still popping enough it would not run right driving. Valves are all in speck, timing is on, carb is clean, new spark plug, good compression. Don't know where to go from here.

 

If it's still popping back through the carb then somethings still wrong. If it came in this way possible that it's an electrical problem,breaking down that could have caused a back fire that may have sheared the flywheel key in the first place. If you're sure the mechanical timing is good,cam and valves ok,carb ok,then that's be my guess.You can hook a timing light up to the plug wire and see if the light is continuous or intermittent as rpm increases up until when the engine backfires.This is just one old fashioned way off telling that it might be an electrical problem that started all this mess. In a case like this a 5 buck manual that gives stator,coil specs and other electrical trouble shooting guides can help narrow it down.2008 Polaris Sportsman 500 Service Manual PDF Download