Hi,
I have a 2000 Trailblazer 250 that is giving me a problem I don't understand. I have a HOTSEAT exhaust, and an EPI clutch kit that has an orange spring exposed(I guess the primary). Everything else is stock to the best of my knowledge. I'm not certain if a 140 main jet is stock, but the plug burns brown so the mixture is good. The cylinder holds 120 PSI > 2 minutes.
Here's my question for some of you Polaris pro's out there... If I just toodle around for ~ 10 minutes to warm up the machine and then nail it from a stop on tacky clay soil I get a boggy response, front tires seem almost glued to the ground and power seems to be only midrange. I just thought for the longest time the TB 250 power was exactly that... Until one morning while camping with the quads. As soon as I could shut off the choke, I nailed it a bit to get going as normal and it stood up. For the next 5 minutes I had no problem getting the front wheels off the ground, even in light gravel. But soon thereafter, back to the midrange only power. What is it that could be so different while the machine is cold? I claim no expertise in the PVT area and believe that is where the problem lies. This problem is repeatable as long as the quad has been sitting for 2-3 hours. I took the cover off the PVT(as instructed by the local dealer) and watched for smooth transition on the clutch. I see that at a slight thottle increase the clutch moves ~ 1/4" down the shaft and can feel the initial engagement. Then it smoothly moves along the shaft until I'm completely through midrange which I guess is normal.
Any insight would be greatly appreciated.

 

The motor is air cooled so when it gets hotter its not going to give you the best performance and when its cool its going to run a lot better.

 

DGPolaris has a good point. Also, I wonder if you are too rich on your pilot or needle jet. A colder engine and cooler air temps like more fuel (richer jetting), so maybe that is why it responded so well that one time. Don't forget that a nice 'brown' color on your plug may be more representative of the main jet and not your pilot if you ride mid - to wide open throttle a lot. If you were to put a new spark plug in there, ride the atv around for about 15-20 minutes and never exceed 1/4 throttle (ideally staying around 1/8 throttle), stop the engine, pull the plug, and inspect it and if it were still brown, then I would say your pilot jet is OK. My guess is that the plug will be very wet / oily. That blubber or hesitation that you feel is probably in the jetting. The PVT will also affect how well you put the power to the rear wheels, but just because you said you were able to make it take off on you one time when it was cold lends me to believe you need to get your engine dialed in better before you mess with the clutch.

 

Excellent idea Polaridoo.. It's funny how easy it is to run out of ideas when it's your own machine..
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I bought the HOTSEAT pipe since it seems to be favored in the community for good hp bang for your buck. I didn't read anything that said it required a jet change though.
Listening much closer and cracking the throttle wide open(in neutral) as quick as my thumb can, I am hearing a bog. My needle jet is in center setting & I dropped the needle down one(then 2 to the top) notch to see if it wanted more fuel. That wasn't the case. I also tried raising the needle jet 1 notch at a time with a noticable loss of power midrange. Just too lean at this point.
The bog is there(idle to 2K-3K RPMS) no matter where I set the needle, so it's back at midrange where the plug burns nice @ mid-high rpm riding that I do.
The bog is then in the pilot circuit is it not? Once the engine gets to ~3K RPMS it revs up very quickly and raps nicely. The pilot circuit is a combo of the main/needle jet and the pilot from what I remember. Anyone know what is stock for the pilot and if a 140 Mainjet is correct for the stock carb?

Thanks for all the feedback. Maybe I'll soon be able to beat my 8yr old son off the line as he rides a 2002 Sportsman. [img]i/expressions/face-icon-small-mad.gif[/img]

 

Forgot to mention my son's 2002 Sportsman is a 90cc...

 

if the engine is running great while it is cold and once you got it open up for some time then it's loss power that mean is too rich,if it loose power when cold that mean it's too lean,,pretty inconsistent pwerformances can came from the air-cooled motor once every while,,
that just normal heat cyle pain,the 400 suffer bad from this too when coolant is not drained on a regular basis.

 

You seem to be on the right path with your diagnostics. Keep 'fiddling' with the jetting until you get it optimized. Really, the only true way to jet is from the bottom up. So you want to make sure you get your pilot right before you move to your needle and the main. The reason for this is because there is always a tiny bit of overlap in circuits.

If you have owned other air cooled 2 strokes and this one seems to be acting much different, then it probably is in your jetting (and perhpas a bit in your clutching). Air cooled 2 strokes definitely lose a bit of power when they warm up and normally need to be jetted a slight bit rich to protect them against burning down (detonation.. heat... all that)