kx 125 jetting or clutch problems

[jdager]

Hi all,
I just bought a 1984 kx125 I am having a few problems with. I can start it up easily and it runs good. I can rev it all the way through the powerband in neutral, with no hesitation, but when I put it into gear, when I try to go, I have to give it a lot of gas, and very slowly feather the clutch to get it to get going, once I am moving at a descent clip, it screams, but if the rpms fall into the lower half of the rpm range, it seems to bog out. I initially thought it was a jetting problem, but I was wondering if it would still act up in neutral. also, the bike doesnt seem to smoke too much, and the plug looks great, chocolate brown, and doesnt fowl. I am wondering if this is more likely a tranny issue, and if so, where I can start to look? thanks for the ideas
Jim Dager

 

[_JOE_]

Do you have experience with an old 125 2t? They have ZERO bottom end. That being said, it's possible the compression is getting low.

 

[digifox]

Do you have experience with an old 125 2t? They have ZERO bottom end. That being said, it's possible the compression is getting low.

 

[jdager]

no, this is the first one I have rode older than a 98 kx125, so maybe that is it. I think the compression is good, it was just rebuilt, and it has much more compression by feel than my 2000 kx125, and that one has about 150 psi. any other ideas, or is it all just in my head?
thanks,
Jim

 

[yz80nbeast]

my 1985 yz80 did the same thing when the clutch was burning out time to change those plates

 

[_JOE_]

Does it have a power valve? If not that is probly why it feels so weak on the bottom. The PV in a modern bike changes the port timing at lower rpm letting the engine build better low end.