99 Polaris Sportsman 335, idles fine but when you give it gas it sounds like it bogging out. We have replaced plug and needle and seat. Runs even worse with the air cleaner on. Help
It sounds like the camshaft is going flat. The exhaust lobe on the camshaft is the first to wear. Basically the exhaust isn't opening the entire duration it needs to expel the exhaust. This will cause the bogging issue. Polaris uses an overhead camshaft, which fortunately, makes it easier to replace. To check the camshaft:
1. Remove spark plug
2. Remove the large bolt on top of the recoil starter
3. Rotate the engine with the pull rope until the "T" mark on the flywheel is visible through the hole the bolt was removed from
4. Remove 8 screws on valve cover, fuel tank removal is not necessary but gives you more room
5. Remove 4 bolts from rocker arms, lift rocker arms off camshaft
6. Rotate engine again with pull rope to inspect camshaft. The center of the camshaft is the exhaust lobe, intake lobes are on the outsides of cam. The exhaust lobe should be about the same height as the intake lobes, and will be noticeably flat
To replace the camshaft:
1. Remove camshaft gear access cover on right side of engine
2. Rotate engine again until the "T" mark on flywheel is visible, 2 dots on the camshaft gear should be at the top of the gear and will be parallel to the mating surface of the valve cover
3. Locate the chain tensioner, 2 small bolts holding tensioner to cylinder and 1 large bolt in the center. Remove the large center bolt to remove tension. There will be a spring and pin inside tensioner so be careful not to let it fly out.
4. Remove screws holding gear to camshaft, leave the gear on the chain
5. On the left side of the engine, clamp the coolant hose going into the thermostat cover
6. Remove thermostat cover, some coolant will come out but is ok
7. There will be a round cover on left side of engine with 3 screws, remove that cover and pull the camshaft out through that hole.
8. Install new camshaft, make sure the automatic decompression lever does not come out while handling. Keep pressure on decompression lever and hold cam so that the little ball inside the cam is facing downwards, this will help to keep the lever inside the cam
9. Install cover on the left side
10. Install cam gear on camshaft
11. Remove exhaust rocker arm from the shaft and replace with a new exhaust rocker arm
12. Install spring, pin, and bolt in tensioner once the gear is in place
13. Install rocker arms, set valve clearance to .006 in for intake and exhaust
14. Reinstall covers and thermostat cover
15. Option B is to take it to a Polaris dealer to avoid the hassle of trying to do it yourself!
Hope this helps, if you need any more assistance let me know, Daniel
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