I have a KLX250s that I bought used with the Bill Blue 351 kit installed. Since I got it, the bike has run decently but not great -- for a while I had terrible gas mileage and was running rich despite trying to tune the carb. I tore it down and found the valve seats in pretty bad shape, had the head remachined, reshimmed the valve, replaced rings, replaced some parts in the carb, and it ran better but still not great (better mileage). It has pretty much always had (and still has) an inconsistent idle, RPM hangs, etc, but seems to get around just fine enough. Now, about 500mi later I lent it to a friend who had overheating problems in the desert (100deg heat and fully loaded, so maybe natural) so I decided to check up on her again.

The plug is caked black and dry, I get about 90psi compression, and the most confounding thing is my leakdown test shows 50-60% loss. I wouldn't call myself super expert, but I followed the instructions, did the test a few different times on different days. Took the covers off, one of my intake valve clearances is just barely out of spec but the others are fine. I can definitely hear air coming thru the crankcase (via the port on the case where you manually turn the crank) and can not hear air thru the exhaust or intake

I would think with that kind of leaking the bike would struggle to run at all???

 

Probably an issue with ring sealing.
If it was severely overheated, the rings may have lost their tension.
If you're not hearing air escaping through the intake or exhaust, it has to get past the rings.

 

I don't have my manual handy, but does the shop manual mention if the KACR can interfere with a leak down test? I don't think it does the way it's designed, so a leak down test should work fine. I've never done a leak down on a KACR equipped Kawasaki. On the compression test, the KACR clearly does interfere with the test, but they still provide a range which is within spec in the manual. It is lower than what the engine actually has for compression.

 

As I recall from many years ago, the leak down test is done with the piston near TDC on the compression stroke. The ACR is not holding the exhaust valve open at that setting, so it won't be interfering with the test.

Ride on
Brewster