Hi all,

Here's the scenario. I have a 95 polaris xplorer 400 2 stroke. It won't idle for more than 5-10 sec and when I give it throttle is will bog and die. Sometimes it will backfire. Takes a while to start again, gotta help it with the starter until it starts to fire.

This is what I have done to troubleshoot.

- pulled carb, tore down, soaked overnight and cleaned with air compressor.
- installed new reed valves (old ones looked good but figure since I am in there, good time to do it)
- new air cleaner
- new plug
- new fuel filter
- adjusted air screw from all the way in to 2 full turns out, very little effect
- tried with choke, without choke, worse with choke, usally won't fire then
- when I had it running and 1/4-1/2 throttle, pressed the reverse override, no difference
- fresh 89 octane fuel
- tank had some junk in it and did my best to clean it out before putting in new fuel
- added a little isopropyl heet
- covered air intake, no difference
- shot carb cleaner into air intake, seems to flood then

One thing I tried was to eliminate the fuel supply. I noticed that with fuel petcock on, slight trickle, reserve gave better flow but not as much as I was expecting. I pulled my tank and hose off my lawn tractor and bypassed atv fuel line and filter and ran it straight from the mower tank to the carb without a fuel filter. That fuel flow is significantly better than coming from the atv tank. This is how I got the most difference in idling, but it still bogs at half throttle and eventually kills. I can get it to idle for longer periods (20-30 secs) and it idles smoother with the mower gas tank connected.

It does seem to smoke more than usual.

Don't know if this is related or not but coincidently, the problems started after this happened. One of the pipe springs popped off on the exhaust manifold and the pipe slid off the jug. I got it back on and replaced the spring. I did start it with the pipe off the jug and this problem was present before reconnecting pipe to jug.

About 2 months ago I brought it in to get serviced because it quit running. Mechanic told me there was water in the tank, lines and carb. They cleaned it and it ran fine after that. 450.00 later. I am trying to avoid that kinda of bill again.

Suggestions?

 

did you do a compression test? how did the plug look when you changed it?

 

i would definatly check compression. after that i would check for and air leak somewhere

 

I have not done a compression test yet. I really am hoping that isn't what it is. I have rebuilt the top end twice in the last 4 years and the bottom end once. If I have to do it again, i will have to get rid of it. Too much nickel and dimes for this dog.

The plug was dark and oily. This has alway been the way plugs look when I replace them since I have had this machine.

 

plug should be a nice tanish color. slight hints of oil is ok on a 2 stroker. shouldnt have carbon buildup tho.
when the exhaust came off was the engine run in dusty conditions. the motor does suck exhaust back into the cylinder while running. it could have sucked dust in and messed the rings up.

 

Wasn't run in dusty conditions. The kid fired it up and realized something was amiss when it broke his ear drums so he killed it right away. I ran it and moved it about 50ft in the yard to the ship, so should be good there. Thanks for the feedback on the plugs. They looked the same as they do from my 95 skidoo STX so I figured it seemed to be ok.

 

Compression is 100 psi. Seems low. What are the next steps?

 

100 psi is the absolute lowest reading that it could still run. next step is to bore the topend with a new piston

 

Update:
I rechecked the compression with a new guage and it's 120 PSI. So I began working on spark and found that I didn't have any. Swapped out CDI unit, ignition coil/plug wire with a buddies and spark came around and then swapped my old parts back. We also pulled the black lead on the CDI which disables override and stop switch. Spark was better, but it still having problems starting. won't idle, bogs, sometimes backfires. We also swapped carbs with the same net effect. I sprayed carb cleaner on the intake between carb and jug, didn't notice any difference.

Thoughts?

 

Have you checked the stator?
I now see this is an older post