yz 125 loading up?

[Howser]

i have a 93 yz 125 that runs decent but seems to load up on the low end and be down on power in the low end right up into most of the mid range. i cant seem to find much information about the jetting, needle clip position and air screw position as far as how it came stock. i know it came with a 330 main jet, 20 pilot and a 56 needle but no luck on clip position.as of now i have the clip on the second notch down and the air screw i have tried in many spots. At 1.5 turns on the screw it still seems to want to load up but when i try any more than 2 turns it idles high but runs slightly better. but regardless of air screw position when i let the bike idle down it will idle good for a little bit then start loading up again and i have to play with the throttle to keep it from stalling.
i got the bike giving to me as a gift and have been trying to fix it up. when i took the carb off for the first time it didnt even have the needle retainer so the needle just kind floated around it there. so i went and bought that little 25 dollar plastic piece thinking it would fix my problem but it didnt. it made it a little bit better but not fixed it.
the first time i took the head pipe off (stock) it had so much carbon build up right off the from the edge of the exhaust port far down into the pipe, i couldnt believe it. i cleaned it all up the best i could (from what i can see) but with still no luck.
i have taken the cylinder off and it has a wiseco piston. with the cylinder off i cleaned it up and put it back together. i can open the power valve open easy so i dont think its sticking/stuck. oh and it blew 135psi of on my compression tester with about 15 kicks.
really sorry for the long thread guys but i just really want to figure this problem out. i know these bikes dont have the best low end any way but it shouldnt be like it is i know that. with that much carbon build up in the pipe do you think it could have a bad crank seal causing it to burn tranny fluid and cause my issue if thats even possible? any help or thoughts would be great guys. thanks for your time to read my long thread.

 

[helio lucas]

well, i guess you hit the nail. so much carbon build up usually is the right crank seal. they are cheap so just replace both of them. the left one is behind the stator and you can just pull it out with a small screw driver. the right one is more difficult since you have to drain the oil, pull the clutch cover and the clutch assembly to get access.
also make sure you have no leak on the carb boot and on the head gasket. :cool:

if you don´t have a service manual, get one. they are invaluable and should help you in the task.

 

[Howser]

well i guess ill start with the crank seal and see how it goes from there and report back....

oh and how do i know where to set the carb slide height?

 

[helio lucas]

i am not sure what do you mean with carb slide height.
you have two screws on the carb. the one in the middle controls the idle air flow, the other controls the fuel mixture. to adjust to more air flow you just turn the screw in, it will be yeld by hold the carb slide from being totally closed.
if you mean the needle on the carb slide, then the middle position is a good start.

here is a link to carb fine tuning (jetting) process to help you to understand the basic procedure :cool:
http://justkdx.dirtrider.net/carbtuning.html

 

[Howser]

the adjuster in the center of the top of the carb is the one im talking about. the more i turn it in/out the more it lowers/raises the slide. its my understanding that the idle is adjusted from the adjuster screw on the side of the carb(not the mixture screw) and the slide is set to a certain height from the top of the carb. any small engine i have worked on has had a set carb slide height but maybe these Yz's are different...

 

[helio lucas]

the two screws act together. the simple way is: turn the air screw until the engine idles but not too high. then turn the mixture screw until the engine gets the highest possible idle. after that, simple turn the air screw again to get the best possible idle.
this is pretty basic but will get you clode enough.