Ok, so I'm rebuilding my 250 for next race season, and I figured I'd go +2mm over while I'm at it.

I called Duncan Racing and they said it wasn't worth it, and it could cause "reliability issues". Now I cant quite see what issues could possibly arrise from a little boring, so I poked my head around a little and talked to some people that did +2mm bores on 85-86 models. They all said that is wakes the bike up a little and doesn't cause any problems.

So, I sent my cylinder out, and I'm gonna go for it. But I was just sort of thinking, what "reliability issues" was Duncan Racing talking about?

 

mainly overheating, i would think , make sure your jetting is spot on , runing to rich/lean, can cause prob's , not an expert on you'r bike but you should get a lite
piston to offset the weight of the over bore, make sure you break it in like you plan on riding it!

 

ok, maybe ill get one of those little billet inline coolers, too. and what exactly do you mean by "break it in like you plan on riding it"?

 

when you break in the rings i personaly found the bset way to get the rings to seal good [ no blowby] is after warming it up run it hard , [no prolonged hi rpm mind you] but run it , the cylnder pressure help's . alot of people let there motor idle, and don't rev it up , the rings themselves don't have the presure to seal by them selves hope this helps, my 2 cent's

 

by the way i run one of them cooler's on my cr 500, and my ds 650, can't swear to it , but it seem, to help, i don't have any overheating issues .

 

alright thanks alot man, as a matter of fact i've heard quite alot on the break-in procedure debate and things seem to lean towards your method so ima go with it!