I have a 2006 TB 330. The issue is the bike start and run. When I say run it runs "ok" it seems to initially be down on power but runs ok. You can drive it up and down the street for several minutes. After about 3-5 min the bike runs worse and worse going slower and slower and then eventually dies. Once it has died it will not restart. After some time (I have never timed it) it will start fine and the same cycle continues.


I have cleaned the carb and new jets.
Replaced the fuel pump.
New spark plug.


It seems as if over time the engine slowly starts starving for fuel. Like the fuel pump can't keep the bowl full (which is why I replaced the pump).


I'm pretty stumped. Any educated guesses would be appreciated.

 

Check the valve clearance when cold. Should be .006 intake and exhaust. Then do a compression test. With the decompression device on the cam, the manual says you should get between 70-90 psi standard compression. If lower than this could be piston rings are loosing a tight seal against the cylinder walls when hot and looses power and dies.For a more accurate test a leak down test can point out where an engine looses compression. Either through the intake valve,can hear air hiss through the back of the carb, exhaust valve, can hear air hiss through the muffler or the piston and rings,can hear an air hiss through the crank case vent hose. Or even possibly through all! 10% loss is max loss allowed on any leakage. Either way,sounds like you need to address this fairly quick in case it is a piston to keep it from breaking and causing even more damage. Here's a simple video on a lawn mower ,but uses the same principle. PLUS you can pull the plug when it does this and make sure you still have spark. If not mechanical,could be an electrical problem that breaks down when hot..

 

Thanks old Polaris tech, I will look into that, however I have never run a compression test before, I'm sure I can pick up a tester and follow the vid instructions. Perhaps dumb question, but how do you know your piston is at TDC? what is the easiest way to find TDC?


Also, if you don't mind moving onto a 2nd possible solution, if we assume the bike leaks down "fine" then where do I look?


admittedly, this bike as been neglected. It's kind of the "red headed step child" it's just an extra bike I have for kids to ride. It seems every year it has "issues" after a long rest over winter but every spring once you get it up and running (maybe with some starter fluid) it ran fine. Not fine like perfect but fine like good enough for the kids.


Thanks again for any input.

 

Easiest way to get to tdc is to pull the spark plug,pull the intake valve cover,then pull the recoil and watch the intake rocker arm go down. As the rocker arm rises,have a straw in the plug hole and watch as the straw rises to it's highest point. This is one way to get close to tdc with out having to pull the cam cover and looking at the index marks on the cam. Plus you have a 14mm plug on the recoil cover that you can remove and see if you can see the tdc mark on the flywheel line up with the case pointer. Then you can at least check/adjust valve clearance on both valves,then do the compression check. If it turns out to not be a mechanical but an electrical problem,you need to check resistance on the stator,coil and go by the trouble shooting guide the service manual shows.That's where the 5 buck manual can save you time,headaches and money. 2006 Polaris Trail Boss 330 Service Manual PDF Download