Need help

[pault]

I have a 2008 Polaris sportman 400. Went riding last weekend an it started losing power. At wide open throttle, max speed was 13 MPH. I drained and replaced the fuel and cleaned the air filter and its doing the same thing. It will start and idle, but loses speed and power while riding. Any suggestions. Thanks

[Chevy1500z71]

theres a few things id check. first of all, check the quality of your gas, drain some into a glass jar and wait a few minutes and see if the jar of gas becomes half water, half gas.

second, your carb is probably a mikuni cv series or something like it, meaning it has a vacuum slide. iv seen the diaphragm on the top of the slide get ripped causing the slide to never open. if your diaphragm is ripped, you can give it throttle and open the buterfly up all you want, but the slide wont follow. this causes effects pretty similar to what you describe. iv seen this happen from the rivets that attach diaphragm to the carb just becoming loose, but if your only going 13mph, id have to think you have a big rip.

you may also want to just go through your carb and make sure no jets are clogged up.

[pault]

Thank you sir. I drained the gas and spark plug, added 2 gallons of fresh gas and added some Sea Foam. It idles better and only misses a little when wide open and I can get it up to 25 MPH. I want to run the sea foam through it and see what happens. Worst case is I will disassemble and clean the carb. The diaphragm your refering to must be the one I see at the very top of the carb. under a 3 inch round disk. FYI, the old plug was black and covered with soot. Thanks for the help.

[Chevy1500z71]

yup, the black plastic round cover on top is where the diaphragm is under.

sounds to me like new gas fixed half the problem, if the gas you drained out wasn't any good, you can bet the carb has gotten fouled up from it. the moisture that this ethanol blend gas attracts creates a gelly sludge in the carb in no time. sea foam is never a bad idea, i like to use it along side of a vacuum clean. alot of times if i bike is running a little rough i can save the time of taking the carb apart by doing a "vacuum clean", i take the airfilter off and rev the motor up, as the rpms run up ill put my hand over the intake to cut the air going in, at this point id also open the throttle completely, you will see the intake tube collapse from the extreme vacuum. ill just sit there with the throttle wide open and control the rpms from going to high by slaping my hand over the intake over and over. let it wind up, cut it off until its ready to die and then pull your hand off and let it wind up again. alot of times the high vacuum will suck any any junk from the jets, doesnt always work but its a little trick that iv used from time to time. when your pouring the seafaom in the intake youl notice its difficult to get the motor to consume the seafoam because the vacuum slide never wants to really open up in neutral, do the vacuum clean trick and youl really move some sea foam through the engine.

so next time your buddys bike is running a little rough while your out riding, show him your new trick you learned on the forum lol.

[pault]

Thanks for the trick. I will give it a shot and thanks for the advice.