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View Full Version : 39MM OR 40MM fcr


neals03400
03-04-2003, 08:43 PM
i heard there was a new 40mm FCR carb. i have a 03 400ex with 11:1 piston stage 2 hot cam ported polished head. whitch carb should i run,the 39 or the 40
Mr_Bub400ex
03-04-2003, 08:52 PM
im thinking bigger is better? or bigger is more gas?
Extremeracer167
03-04-2003, 08:53 PM
still stock bore?? Stay with a 39mm
Mr_Bub400ex
03-04-2003, 08:58 PM
would it hurt to go up the 40 or 41mm?
neals03400
03-05-2003, 09:23 AM
what kind of power gains do you get. yes i still have stock bore.
Scott400EX
03-05-2003, 09:26 AM
I would think anywhere from 3 to 5 hp with the 39mm. ( im guessing)

Are you going to Bucleberrys this saturday neal?
Scott400EX
03-05-2003, 09:26 AM
I would think anywhere from 3 to 5 hp with the 39mm. ( im guessing)

Are you going to Bucks this saturday neal?
Extremeracer167
03-05-2003, 09:36 AM
well u will lose bottom end if u jumped to the bigger carb, but gain top end. But if your stock bore, ide stay with a 39mm.
Scott400EX
03-05-2003, 09:42 AM
What about if you plan to go to a 426 bore and 4mm stroke. ( i thinnk that 451 or somthing likt that) would a 40mm or 41mm be ok to run with stock bore for now till that engine work takes place?
airheadedduner
03-05-2003, 10:04 AM
When looking into a carb you always want to err twards a smaller carb. A small carb will hurt your performance less then an overly big one.
Extremeracer167
03-05-2003, 11:07 AM
TC sais that if u are gonna go with any carb for even his 465 stroker kit, the biggest he reccommends is the 40mm FCR(off a CRF450 i believe). But ide still stick with a 39mm
neals03400
03-05-2003, 02:40 PM
yeah scott well be there saturday.