Hello,I just put a new top end in a 2004 kx250(ran before, bought it used and it was what appeared to be the original top end). after re assembling(also cleaned power valves,had some help timing those) it won't start. I did get it to fire for about 3 secs 2 times. I have spark(although it is more white than blue), compression is 110(which seems low to me although rings haven't seated in). I even squirted fuel directly into cylinder and nothing.I took the reeds out and noticed there are small gaps on the side,but not the front( v-force delta 2), would they have worked with the old worn out top end and not the new one? I have tried 2 different plugs. Never had this problem-it's a 2 stroke!Any tips would be awesome.Thanks,
Hello how are you
Your compression readings are way low. Is the cylinder sleeved?
No it's not, the cycle shop said it looks OK(no score marks-just slight discoloring in a few spots-I measured approx. .0025" with the new piston on the skirt to wall.
Give me a moment to look a couple things up. Have you measured ring end gap in a couple different spots in the cylinder?
I did in just on spot and filed one ring.
What is / was the gap?
Fyi , compression min is 119psi, normal is right around 185 psi
the top I think was .009 and the bottom was .013. I never have done this before(just always put the rings in- no problem-now I take my time and might have fubarred it!
Ok looking up the info now
I just used some 400 grit paper and sanded one end of the ring(is this correct?).
End gap should be .0098-.0177 in
My thoughts on this is the cylinder is worn, I will post those numbers for you as well. one moment
Maybe I should have the cylinder checked by machine shop and order up some new rings. Do you think the reeds would affect this?
2.617 or more then .020 difference between any two measurements. That is the service limit
Reeds will not cause this. Didnt you just install new rings?
Yes I did just put in new rings, but maybe I filed too much- didn't measure accurately? Don't know as the bike ran before and now it doesn't. Would air gaps in the reed sides cause issues?
That will not cause a reduction in compression.
Sorry air gaps will not cause this however filing the rings too much will
Have everything measured before ordering parts that may not be needed
I think I need to take it apart and and have it re plated. Can I use a Wiseco with a fresh re plate-I heard you need a couple thou. more clearance than a cast piston?
Yes you can, i will also provide you with the piston - wall clearance
Ok sounds good
So I should have higher than 120psi even before the rings seat?
If you have any further questions let me know. Please remember to rate my answer ok service or better so i can be compensated for my time...Thanks
Ok, thanks-just never had this problem-think I might have filed too much
20 years of experience in mostly but not limited to metric machines including atv, watercraft ,mule