Carb Question

[Blackpaladin]

I have a 1994 Yamaha Banchee with a 1986 250R motor in it. Upon taking the top end apart to figure out what kind of work had been done to the motor, I measured the piston to be 84mm wide, and some port and polish work to the jug. I am running a full FMF pipe/silencer combo, I think the reeds are stock, and so is the cage. I did replace the carb with a 38mm Mikuni model from Denniskirk.com. What I would like to know is what kind of jetting should be in this carb for the above motor setup, and could someone recommend a reed/reed cage setup for me? Thanks

[wilkin250r]

Are you sure you measured that correctly? An 84mm piston would be 400cc on the stock stroke. That's HUGE, there is only one company I know that makes a top-end kit that size. I'm not saying it's impossible, just REALLY unlikely.

If you DO have that top end kit, I'm almost certain it's not the stock reed cage.

I'm sure we can help you, but first we need to all be on the same page, talking the same language, and make sure our information is correct, because the bore size is going to have a big impact on your jetting.

On a side note, your combination is really odd (be prepared for negative comments about it). Where/Why on earth would you have a banshee frame with a 250r motor?!?:huh

[Blackpaladin]

Negitive comments??:( I don't know why the combination, I just bought it that way. It is a 94 Banchee frame, and an 86 ATC 250r swingarm, rear suspension, and motor. When I measured the piston I measured across and although it was with a ruler and not a caliper, it was 84mm take or leave 2 mm. On a side note, would it really be a 400? I thought it would be more like a 310.

[250r rider 88]

84 mm piston would be exactly 398.8 cc with stock stroke
beerocks sticly at the top of the page can help you figure this out ur piston is 84 mm divide by 2 is 42 move dedimal over make it 4.2 times by pie which is 3.14 times the stroke 7.2 and then again by the piston size 4.2 gives you the above cc measurement i would recommend going to your local hardware store and pick up a plastic caliper with metric measurements and get the right number

or if you can get the numbers off of the piston we can tell you the piston size

hope thats helps

[kiesta00]

Originally posted by Blackpaladin
Negitive comments??:( I don't know why the combination, I just bought it that way. It is a 94 Banchee frame, and an 86 ATC 250r swingarm, rear suspension, and motor. When I measured the piston I measured across and although it was with a ruler and not a caliper, it was 84mm take or leave 2 mm. On a side note, would it really be a 400? I thought it would be more like a 310.


banShee frame, 86 atc swingarm, motor? lets see some pics of this beast