I have a 07 250s with hmf can, 45t sprocket, air box lid removed, rejet stock carb, fsw head pipe, crank case breather mod, air injection removed, uni filter, and air box screen removed. What mods are involved to install a tm 36-68 pumper carb? I hear they really help performance. A big bore kit will be added later. I need some advice on this matter.

 

skip the carb and go straight to the big bore

 

With the stock tank, there really isn't any mods needed to install a TM36, it's just a bolt-in. You have to modify the throttle wheel to get it to clear a Clarke tank though. I've only ever used the pull cable, so I don't know what's needed to get the push cable hooked up.

If your heart is set on a pumper carb and you're going to add a big-bore kit, I'd suggest doing both at the same time. That will save you from having to jet and adjust the carb twice. If you can only afford one at a time, I'd also suggest doing the big-bore first. I know some guys are running a TM36 with the stock bore, but it really works best with the extra vacuum signal that more CC's give.

 

Thanks for the info guys. Mustang is your 340 kit from Bill Blue? How much difference did it make on your bike?

 

I have his 331 kit with the pumper. Did the pumper first for about a year then did the big bore last november.

 

I was told the 250 and 300 is the same engine as far as balance goes, and the factory didn't rebalance for the lighter 250 piston. Is that true? Do you notice any more vibration, if any with the 331 kit? I was told the 351 piston is the same weight as the 300 and would bring the engine back in balance. Is that true? I use to build v8 racing engines for a living , and I'm trying to stay away from any balance problems. Thanks.

 

I got my 340 kit from Thumper Racing. I installed the big-bore kit and a pumper carb together, and the difference from stock was night and day. Most notable was the increase in bottom-end torque and throttle response. I didn't notice any more vibration over stock, just boat-loads more power, and more power right now.

I don't know this as fact, but I would imagine all of the pistons with the various big-bore kits are about the same weight as the stock piston. Otherwise, like you said, the reciprocating assembly would be out of balance, and the engine would be able to shake paint at idle.