Stock 400 except for K&N filter, pilot jet to #40.
First gear is great, pulls the front end right up. Second gear falls on it's face - no power, even when droppin the clutch... any ideas? I checked the plug burn and it's perfect????

 

Maybe try like a 155 main jet?

 

clean you filter and fuel line. they may be clogged

 

check the boot that goes into the carb. Mine keeps poping off causeing my mid to high end to bog down...It comes off every time I ride.

 

Turn the petcock to off and remove the 17mm cap from the bottom of the carb, then unscrew the main jet. It should be around #148 as I recall. Sounds like your main jet is too lean (need at least the #148).

 

Main jet is OK, plug looks good.. I drained the gas tank and dumped high octane in, made quite a bit difference. Pulls hard in first ok in second and can start in third without stallin.

 

check your vacume needle slide in the carb. They have been knowen to stick. If you have a K&N filter get rid of it.They do not work very good. Put your hand inside the intake boot and you will fill the grit that stickes the sides.