Ok, I've worked on dirt bikes and atv's most of my life. I rebuilt a-many motors and never seen this. All the 2 strokes I've worked on had reed valves. I have even seen rotorary/port injected 2 strokes but never just the carb going into the cylinder the way the polaris does. I thought there was something wrong with it and maybe someone was messing around. I looked the polaris parts up on a parts fiche and there is no reed valve installed. This quad just had the top end rebuilt and starts great now but bogs out on the top end bad. The carb is cleaned and it is getting plenty of gas. What could be wrong?

Thanks for your help,
Otto

 

Otto, the 250 is a piston port engine,one of the first 2-stroke designs invented. Long before the rotary valve and reed valve came along, the little put-put piston port has been chugging along! There are fellas on this forum that can help you get a little more out of it,BUT dont expect a fire breathing monster! As far as bogging out on top end you can start by raising and lowering the carb needle a couple positions and see if it helps either way. Also see if it runs better at top end with the choke pulled out a tad,if does then upping main jet may help. Good luck OPT

 

just like all the 2 strokes, reading the spark plug wil tell you if it running rich or lean. is it stock? clutch,air box/filter, piped? if all stock, then the needle clip shouldn't need to be raised to run correctly if everything else if fine. imo

 

With proper porting pipe and clutching these 250s will run with most stock 400s

 

it does have an aftermarket expansion chamber but everything else is stock. I will try the chock thing on the top end speed to see if it runs a little better. Thanks for the help, I will let you all know what i find out.