YZ 125 Compression?

[KawiRider]

I checked my compression on my YZ 125, 145 PSI. I just bought the bike, and me and my father are going over the whole bike. My repair book said that the compression should be around 120 PSI for a good result. If it is higher, there could be carbon build up, I didn't want to take apart the top end, but if I have to I will. What is the average reading of a good top end for a 1998 YZ 125? Does carbon normally build up on top of the piston? How often should we clean the powervalve? The bike is used for hare scrambles only.
-Thanks for any replies

 

[cr250]

I found that I normally have a little carbon buildup on top of my piston 96 yz 125...proably better than none...Not sure but am very interestyed in the normal value for 125 compression...my 125 seemed to lose compression after I put a new top end in...very strange...
Vanessa

 

[Pit_Monkey]

a strong 125 should have about 150 psi for compression however the average is about 125-135 and a bike will start with as little as 105 -100 psi however it will be very difficult to get it to fir up.;)

 

[KawiRider]

Thanks

Thanks for the great and quick replies!

 

[anton]

Compression

I'm not too sure that there can be a standard. Every type of compression tester comes with a slightly different adapter. Mine came with two, the short one gives 175 psi, the long one 130 psi.
My advice? Buy a tester, the best one, replate your barrel, insert new rings and piston and establish your own benchmark.
Regards
Anton

 

[MikeT]

Originally posted by cr250
my 125 seemed to lose compression after I put a new top end in...very strange...
Vanessa

It will lose compression with a new top end until the new parts get broken in. That is a normal occurance.

 

[cr250]

Ok thanks I was really confused by that for a long long time...The bike has been running great since I rejetted and got new tires. :)
Vanessa