Compression Question

I had never heard of doing compression checks on 2 strokes until the last couple years. I had done it on 4 stroke car engines, but not on 2-smokes. The '85 and '86 are significantly diferent models. The '86 is different inside that cylinder. There is a KIPS exhaust valve on it. What I am getting at is don't make decisions on compression readings alone. I would suggest doing some jetting on the '85 to try to make it stronger.
My '85 did not come with a carb, but I think the one I have is from an '85 KDX200. I have not finished jetting, but it runs OK and starts easily with the following:
pilot jet-40, needle-R6, clip in the top groove, needle jet-5FJ57, main jet-127.5.
I will try to do compression checks on my bikes. The '85 has new piston and rings and the cylinder 'looks' good (I have no ideas what its history is). My '88 is hard to start and I would appreciate your jetting specs. I was told that the top end was recently done on it and I opened it up and it does look very recent.
I would not decide to do a top end job on either one until you open them up, look inside and measure the wear. Contact me directly if I don't get you those compression numbers soon.

Make sure you warm up the bike first. After installing the comp gauge hold the throttle wide open and continue kicking until the gauge stops climbing. I did this on my stock 00 KDX 200 and got a reading of 165lbs, sorry I don't know what your bike should be but anything under 100lbs sounds low.

I think my service manual says it should be around 150lbs but I can't remember exactly.

Compression checks are so subject to variance that they really don't tell you a whole lot. Maybe done the same way with the same guage by the same person on the same bike....that may tell you if something has changed in that bike when you compare measurements taken over time.

Otherwise, you're pretty much wasting your time.

Combustion pressures at kicking speeds have squat to do with what's going on when the engine is running. Besides static compression differences between bikes....port timing, variable port timing assemblies, pipe scavenging..these all will have an effect on combustion pressures.

Comparing one model bike to another doesn't tell you anything.

An extraneous example of dubious import: Manifold vacuum is commonly considered a useful measurement for determining condition of some engine components on 4-stroke motors. It should be around 18-20 inches or so.

My car's engine not only has NO vacuum at idle, but shows pressure spikes at idle. Does that mean my car has something wrong with it?

No. It does mean my engine cost thousands and thousands of dollars.....and is most likely much faster than yours!! ;)

Or (short version) .....don't worry about it. Although 75psi is pretty low...