Need port work and head cutting who to use?

[sangheraent]

I don't understand why people are saying I cant use a yfz for baseline. Im not saying I want to beat him I'm not some rookie who wants to beat their buddy. I can use anything as a baseline as long as it is consistant in its power output. Heck I could use a lawnmower as long as it puts out the exact same power each time. Im not comparing my reaction time in a 100ft drag race, Iv thoroughly tested my bike, rolling starts, full pinned holding different different gearing.

Rablack21 is right the guy is a hack, I have tested everything I tried 3 different carbs, 2 different ignitions, 3 pipes, weeks of jetting, different octane fuels, different reeds, different spark plugs coils.  Like I said the only option that I believe would result in my 310 big bore to have less power then my 262 is poor porting.

[udontknowme]

maybe it doesnt have any porting and you paid for nothing ?  which might be the best thing at this point so your not fixing someone hack job. worst case is its butchered to hell. take some pics and we could give some idea if it looks pooched or not

[JesseA420]

clearly you knew the guy was a hack before you posted here then. also u probably shouldnt have had it built by him after your friend already had him mess up his motor. if you want quality work, go with someone who specializes in whatever given make/model engine you are having built. all the best have been mentioned here, and some have even responded here. good luck.

[Jerry Hall]

................Rablack21 is right the guy is a hack, I have tested everything I tried 3 different carbs, 2 different ignitions, 3 pipes, weeks of jetting, different octane fuels, different reeds, different spark plugs coils.  Like I said the only option that I believe would result in my 310 big bore to have less power then my 262 is poor porting.

I never tried to developed a stock cylinder 262 cc displacement kit.  I would think the porting, head and pipe specs on a 262 would be very close to a well developed OEM 250cc top end.  A well developed OEM top end, stock stroke std bore to 0.50mm over sized piston will make low to mid 50s with a wide power curve and still have a lot of mid range for a 250. I would expect the 262 cc engine to make about 2 to 2.5 more HP than a 250 with similar modifications.  Our old CR250s built in the late 1990s for shifter kart applications would make mid 60s on gas and the micro-sprint CR250s on methanol would make 68 to 72 hp.  I have not done any development on the latest model CR250s but I think I could get more power from these than the 1996-1997 CR250s that we developed.  

A 310 big bore cylinder properly done will make 3 to 5 more HP in the RPM range 1000 to 1500 RPM below the RPM where the engine makes its peak power, than a well developed 250 making the same peak HP.  This 3 to 5 HP more in the mid range is what makes the big bores pull good off the corners and produce really good acceleration in a drag race