RM125 97 rm125 low compression on fresh top end

[Trfsrfr]

I'm gonna go with ran it lean, melted down the piston (and/or cylinder), resulting in low compression for $100 Bob.

 

[Mihylo33]

I'm gonna go with ran it lean, melted down the piston (and/or cylinder), resulting in low compression for $100 Bob.

Thought has crossed my mind....
If that’s your highest bid then I’m going with:
Installing new tire tubes to see if it will start.

 

[2Wheels]

Hmm it’s Wednesday already I would have had it apart in 30 min.

Then again, I have a compression tester too.

 

[Trfsrfr]

Hmm it’s Wednesday already I would have had it apart in 30 min.

30 minutes?
You must be slowing down in your old age.

 

[PALMER84ONE]

140 PSI in a 125 is common upon new rebuild.

Pushing it down with your hand is easy to, but it shouldn't feel like plowing a 40yo hooker, but a tight little fresh hooker.
Just saying.

 

[Trfsrfr]

140 PSI in a 125 is common upon new rebuild.

Well I'm feeling pretty good about my 'new to me yz' then, cuz it has 156.
I was wondering what it should be.

 

[Trfsrfr]

but it shouldn't feel like plowing a 40yo hooker,

You say that like it's a bad thing...

 

[CDA]

4 posts and you guys scared him away..good job!

OP - Did you do a heat cycle on it in the garage after the rebuild or just take it out and pin it? Was the plug fouled from the excess oil when lubing the piston walls during install or did you install dry? I'd pop the head off and see if you are getting blow by pass the rings. what kind of gap you see. Compression tester is good, but if you don't have one, then you are doing the above.

Also as Big D mentioned in the beginning, you did a rebuild, but did you do a carb clean as well?

 

[PALMER84ONE]

Well I'm feeling pretty good about my 'new to me yz' then, cuz it has 156.
I was wondering what it should be.

Remember, gauges can be different, and this is fresh w/o break in.

 

[Rm317]

4 posts and you guys scared him away..good job!

OP - Did you do a heat cycle on it in the garage after the rebuild or just take it out and pin it? Was the plug fouled from the excess oil when lubing the piston walls during install or did you install dry? I'd pop the head off and see if you are getting blow by pass the rings. what kind of gap you see. Compression tester is good, but if you don't have one, then you are doing the above.

Also as Big D mentioned in the beginning, you did a rebuild, but did you do a carb clean as well?

My friend said he did a few heat cycles and rode around but very gently. Plug was new. Ill have to look more into this thanks

 

[Trfsrfr]

Yank the head off. It'll take you 30 mins.
If you need help, ask John.

 

[2Wheels]

hey I can take anything apart.. but I spend 20 minutes digging through all the crap on my bench looking for the tool that I JUST HAD IN MY FKNG HAND

 

[ossagp]

If you can push the kicker down with one hand the compression is too low. If it takes both hands it's just right. Trust me, it's in the manual.

Floyd's uncle "Rooster" told us that if your gf could suck start your bsa that you don't need a vacuum gauge, because she is "just right". I never found that in a bsa manual though (going back to '38).

 

[Mihylo33]

Floyd's uncle "Rooster" told us that if your gf could suck start your bsa that you don't need a vacuum gauge, because she is "just right". I never found that in a bsa manual though (going back to '38).