250r help

[count nesko]

i just got an 86 250r. i want to know what the compression should be at, what would be the minimums before re-ringing, i was told it was bored 040 over and has a fmf gold sieres pipe. what should be the jet sizes and the air box lid is still on, can i take that off? what is a power valve and how can i tell if i have one?

[sly400ex]

Not sure, but fairly accurate......i would re-ring once the compression falls below 140psi, if you take the air box lid off(which is OK if you have a GOOD airfilter) I would start off by getting a main jet around 160 and go from there. If it is a stock cylinder, you DO NOT have PV. A power valve cylinder has a valve mechanism on the exhaust side of the cylinder. It looks like a regular cylinder with a box on the front of it, all molded as one......hope this helps.

[count nesko]

thanks it does help. i have a kn filter and a aftermarket piston don't know what kind tho. i haven't taken it apart to look.
what is normal compression?

[sly400ex]

Again, I'm not positive, but I'd say somewhere in the 180psi range......And something else to think about, there aren't such things as different compression pistons for 2 strokes, you up the compression by milling the head or using thinner head gaskets...and other ways too......

[count nesko]

i have no clue whats been do to it. i just bought it this weekend. and this is my first 2 stroke. and i never delt with a 250r

[250rmike]

a normal freshly rebuilt good running r should have compression around 175. unless it has anything to raise compression i would not let the compression fall below 150-155 before rebuild

Originally posted by count nesko
i just got an 86 250r. i want to know what the compression should be at, what would be the minimums before re-ringing, i was told it was bored 040 over and has a fmf gold sieres pipe. what should be the jet sizes and the air box lid is still on, can i take that off? what is a power valve and how can i tell if i have one? the above statements are true if you have a stock head gasket ,but ..
your compression could be different depending on what head gaskets is being used ..

[count nesko]

how much of a difference does the head gasket make? and then what kind should i get. the head is still stock size and has not been milled and has been bored 080 over

[250rmike]

i dont know the exact difference but get a cr250 head gasket if you want more compression cause it is a thinner gasket. dave please let him know what year cr cause i am really tired and cant remember

every cylinder varies depending on the bore ...
I dont use CR gaskets ...I split the stock trx ..
I have gotten up to 230 lbs in the past

[Bean]

the gasket, and the dome will all change the compression of the piston, but if you have a stock head, that narrows it down to the gasket, and you will probably have either the stock one, a trike one, or the cr one, which i run, im getting around 200lbs on a fresh piston with my dome

[count nesko]

at what point do you need to start mixing race gas. the compression seems high at 230 to be running 93

[310Rduner]

You need to start running race gas at around 185lbs of compression in some engines. Some engines will not detonate until 190lbs, but mine however detonates 93 octane at 185lbs.

I'm running 110 octane Vp-c12 at 185lbs.

Some people will just mix the gas at 185lbs, but i prefer to not have anything to worry about like separation of the two gases or just any kind of freak occurances that somehow manage to find me.:)

[lil400exman]

what year cr gasket do you run? i got a 88 cr headgasket and it doesn not quite fit up right what all years do you guys run?:confused: