I have a 99 explorer 400 that just turned 1000 miles. Anyway when it gets warmed up and about 1/4 to 1/2 throttle it seems to have pre ignition and cuts out from time to time. Open it up and it runs awesome. Going slow it seems to run fine to, just under steady cruising is when I have the most trouble. This is the first time I have ever had to do anything with it. I bought it new changed the air filter and serviced regulary, still has original plug in it, I haven't had to tighten the chain yet, this is really a great machine, it is my first one that I have ever had. Thanks for any input. Also I just took the carb off to make sure it was clean and it is, When it acts up it doesn't get any better when I choke it either so I don't think it is lean.

 

This may not solve your problem, but I change the plug(s) on my 2-strokes at least every year. It's the cheapest, easiest way to eliminate one potential problem before it starts. Less than 2 bucks and 5 minutes.

 

Check your throttlee cable adjustment

 

If it is a light stumble in the mid range, it is probably a little rich. It would be a good idea to have the carb overhauled. What I have heard happens is that over time, the needle and needle jet wear, and make everything rich. I have not experienced this myself, it is just what I have heard from an experienced polaris 2-stroke mechanic.

Waylan

 

Thanks everybody for input.