Yz250 Top End

[eagles22793]

I have a 2000 yz250 that i am doing the top end in it. I been researching and I am not sure if i should get a stock piston and drill out the intake side or get the pro lite piston. I am running 108 octane fuel 40 to 1 mixture with an fmf electronic cdi box. Whick piston is best for my bike and is drilling out the intake side of the piston a good idea?

 

[whenfoxforks-ruled]

Get the wiseco, drill the holes, and run the oil up to 32:1. Then jet the bike. Why 108? high compression, detonation? Vintage Bob

 

[TWRT]

I have never drilled holes in my yz pistons. 00, 01 or 06. I think the holes are for CR types, with a bridge in the center of the power valve area.

Dave

 

[whenfoxforks-ruled]

If they need it, it will come with the directions, should. I have only heard of having the holes on the exhaust bridge. Thanks TWRT. If it has intake bridges, thats different. If the piston is designed to have an intake window, good. I would not make my own if it does not have it though. But, I would make sure any bridge clearance is about .004" to .006". They still seize if they are too tight. Vintage Bob

 

[eagles22793]

I run 108 because I got my head machined down 0.5mm for higher compression and I have an FMF AOF Power Ignition and I dont want to burn my bike up with pump gas. should I just get a wiseco stock piston or the prolite wiseco piston?

 

[whenfoxforks-ruled]

Racing and deal with a shorter ring life, the Pro lite for sure. You cut the head 5mm on a 250, not a big deal. What do you have for a squish clearance? I am still not convinced you need 108 octane of protection. I am pretty sure there is a thread around here about too much octane/you do not need it, will hinder performance. What brand fuel? Vintage Bob

 

[eagles22793]

5mm I am not to sure about that but someone can try besides me I sent the head out and I am going to let the machine shop for dirt bikes figure out the squish clearance beacause I was not sure what to do about that

 

[eagles22793]

I did not start using 108 octane yet but that is what they sell at a dirt bike parts store for dirt bikes and the brand is vp racing fuel the other octane fuel is 93 which is the highest pump gas which one should i use with a fmf power ignition and a head mod

 

[whenfoxforks-ruled]

I sure hope who ever you sent the head to knows what they are doing? Without the rest of the top end, I am suspicious. How do you figure the fancy ignition has effected jetting? Only if the timing is off. I like FMF and all, but they sell power wings also? Vintage Bob

 

[eagles22793]

I am going to call them in a couple of days to go over with them what i want done to the head. I sent it to eric gorr at forward motion I heard they are really good with machining heads. I got a FMF AOF Power Ignition which is a replacment cdi box with a switched that mountes on the handle bars. It have two settings that can be switched from Boost or Torque mode. That is why I am using 108 octane to make sure I wont have preignition or burn the bike up.

 

[whenfoxforks-ruled]

You got the right guy to do the work! When its done, ask Eric what octane fuel the motor needs? Vintage Bob

 

[eagles22793]

I am still going with the 108 octane just because he dose the head he dose not know what is done to my bike so i am going to use 108 only because of the power ignition