KX250 not responding to idle speed screw.......

[IQRaceworks]

I pulled the top end off of my KX250 and rebuilt it with a new piston and rings, and cleaned up the power valve parts. After I got it all back together and fired it up......no matter when I did, I could not get the bike to idle, even if I ran the idle speed screw all the way in.  I tried different pilot screw settings.....everywhere from 1.5 turns out to 3 turns out....nothing make a difference.  I could hold the throttle open a little bit and get it to run down to a pretty low speed, but not really an idle.  Isn't the idle speed screw supposed to lift up the slide a little bit when you screw it in so it will idle faster?  I can bottom out the screw, and it doesn't make a bit of difference.

The motor has great compression now, the reeds are in good shape, the carb has been cleaned, I checked the float level,  and it's jetted close to stock just until I have a chance to get out and ride it and jet it properly.  I'm running a 48 pilot jet, and 165 main.

Any ideas?

[IQRaceworks]

Well....I pulled the pipe off and looked down in the cylinder...CRAP!!   The side of the piston has a rectangular port in it, the port that's supposed to be on the INTAKE side!! Not sure how I screwed that up, I guess I must have had to many other things on my mind at the time. What a bonehead mistake!!  So the piston in in backwards...great!   From what I could tell, nothing looked damaged, the piston and rings looked fine. I only ran the motor for a minute or two, and never rev'd it much past an idle.  I guess I'll pull the jog off tomorrow, and if it all looks decent, I'm just going to turn the piston around, put it all back together, and ride the hell out of it.  I can't believe I put the piston in backwards.......brain fart!!  No wonder it was so hard to start and didn't want to idle unless I gave it a bunch of throttle.

[bens87braap]

done that too just a couple of weeks ago but i noticed before it was too late maybe check to see if the rings are facing the right way up too,  Might have been in the same head space time?  hehe

[KXDINO]

Gee your lucky , heard of a guy with a cr250 do that once , but he kept on riding it till it destroyed it self in less than a hour , sometimes it pays to double check things , or get a manual to see how things go its easy to forget how things go , especially if there left pulled apart for a long time.

[IQRaceworks]

Well I pulled the jug off last night....the only real damage I saw was that one of the rings has a small little chip right on the end of it....other than that, the cylinder and piston looked just fine. I guess I lucked out!  I'm going to pick up a new set of rings, and then put it together the right way!

[IQRaceworks]

Well.....it's amazing how easy the bike starts, and how well it runs if you have the piston the right way!  Once I got the motor back together it took two good kicks and it fired right up into a fast idle.  I let it warm up for about 10min, and then shut it off to let it cool fully.  Then I fired it up again and took a few easy laps around the yard to break in the new rings. Every now and then I would blip the gas....wow, with the powervalve working now it's like a completely different bike.  I can't wait to dial in the jetting a little more and really put it through it's paces!   

[sandblaster]

That's good news but I need pics as I have poor reading comprehension 

[IQRaceworks]

Here are a few pictures.......I've just about got it all finished up.  Just need to put the fork guards on it, and it's ready to ride.  Once of these days I'd like to do something about the wheels....they look pretty crummy.

[sandblaster]

Looks great.
Thanks for posting.

[Foxx4Beaver]

I really like the blacked out look on the 250's...I'll be doing that to mine over the winter.