Hey guys, my kx 250 had a serious loss of power so I did a top end a couple of months ago. My bike has high compression gaskets, full procircuit pipe, wiseco prolite piston, vforce reeds, geared down a tooth on the front sprocket and has a uni filter. Bike has a new plug, and it doesn't foul much, every now and then it will load with fuel. Basically the bike isn't stock but it doesn't have the power of a stock 125 and I can't figure out why? Maybe my kips is not adjusted correct? Could someone post the procedure for setting this? I think the ignition is non adjustable. My clutch is not slipping.

Did you clean the KIPS system and check out all the gears, rods, etc while you were doing the top end? Is the KIPS valve moving?

Did the top-end job help it at all? Or was it still the same after the top-end job?

When you put the cylinder back on did you line up the KIPS lever?

For instructions your better off buying a manual because since it's a little complicated.

I cleaned the valve really well, took it out soaked it in acetone to loosen it up and wire brushed it, it looked new. The top end did make a difference it added a lot of power, but its not where it should be. I've let a few people try it and they said the same thing, its not as powerful as it should be. My buddys stock yz250 has a lot more power, and snappier throttle responce. I did change the shaft and gear on the rod which moves the kips valve, since I didnt realize the nut holding the gear was a reverse thread until it snapped. I lined up the shaft as I was dropping the cylinder down, and I lined up the gear on the valve with the dots if I remember right. did the rebuild in june, and probably put about 30 hours or so on it since then. Would having the kips valve not adjusted right take that much power away or could I have something else more serious going on?

are the reed petals in good condition

yes, they looked new. The bike starts hard, but it has always done that.

The hard starting and low power both make me think about compression. Have you checked it?

Get a manual and take it back apart.

I'll check the compression again, last time I checked it I had somewhere around 145-155psi and that was a month or 2 ago.

wayfast1500 said:

That's way low, assuming your guage is accurate. My KX250 always measures around 195-205 with a fresh top-end.

Did you actually measure the bore and piston when you rebuilt it to make sure the clearance was in spec?

The piston which came out of it was a stock bore, I didn't have bore guages so I miked out the top which I know is wrong but I made sure I was measuring in a area the piston travels.