I was figuring that it had to be something like that.

I have a spare motor that I am working on rebuilding right now.

I'll wait to see what the dealer says. I picked this up as a fun project to do since I like to tinker with stuff but it has turned out to be an exercise in frustration.

 

I had a problem similar to this a couple of years ago.My Sport would start to stutter and die and the RPM's would surge before it finally died after about 550-600 feet of being ran at wide open throttle, I was racing at my local 1/8th mile IHRA Dragstrip.My problem turned out to be that my fuel petcock was starting to get clogged and couldn't get enough fuel to my carb to keep the bowl full at wide open throttle.I fixed my problem by just switching it to the reserve setting and not using the regular setting on the fuel petcock.

It took me a couple of days of switching out fuel lines, replacing the fuel filter, checking different things on my carb and checking for air leaks around the intake boot, cylinder and reed cage before I finally tried the simplest thing that I could think of.

 

I have the exact problem as described to the letter. Did anyone have a fix?

 

What machine do you have. Year and model?

 

99 Polaris scrambler 400 2 stroke. Exact same symptoms as original post. I have done all the same fixes as the original post, was hoping to see the cause. Top end redone because of age and found broken piston skirts on old piston.

 

What a lot of people do is replace the top end only and don't install a new rod kit,crank bearings and seals.If you have good fuel flow,the carb is clean,have good spark,even with a new top end, if crank seals are leaking it could cause problems also.Plus if crank bearings/ lower rod bearing have a lot of play they can take out a new piston if bearings shatter.When piston skirts break it's hard to get all the trash/shavings out of the bottom end.On a 13 year old machine I would always rebuild the whole thing.

 

You definitely need to follow OPT's rebuild program. I had 3 of those '99 Scrambler 400 2 stroke monsters 4x4's. Can't believe that Polaris let that platform die, but on to your issue. A total motor rebuild is in order, pay close attention to the crank seals as well as the water pump assembly, any grooves on the shaft will cause major antifreeze leakage. Also, make sure you go through the oil pump, Polaris didn't do the owners of these machines any favors by dropping the pump in front of the motor and all Mother natures debris. I'm sure you have done the proper cleaning of the carb assembly, and checked the tank for debris. A quality rebuild will make you smile when done right

 

Thanks for the replies. This has been a very good, problem free machine for 14 years. Yep it is probably time to rebuild everything. Kids won't be happy its out of service for a bit though. Thanks again. Also while you guys are on here, any suggestions for a good pipe? 440 Wiesco piston, jetted to 280 ( but can jet to any), and clutch kit. Keep in mind I want to run pump gas only as we go on lengthy road rides a lot.

 

IMO, for the price, go with a new sleeve and back to stock size piston. As for a pipe, pass and get the silencer, AEEN, and Hot Seat, were my choices and performed very well. Spend the money in your clutching (springs, weights & Helix) and gears, as you like those "lengthy road rides". You can run a cut 10K head on Non-Oxy pump Gas at Sea level. With those simple mods, my boys had no trouble hitting 65mph in 2 wheel drive on the '99 "scrammy's".

 

did you get to the bottom of the issue? I’m dealing with the exact same problem.