My 1989 LT250R had gobbs of low end with the stock pipe however the high end power was lacking. I recently put on an FMF Fatty with a Power Core (not a Power Core II)Silencer. Now my low end power is horrible but the top end screams. I was hopeing the Power Valve would help me keep some power on the low end. Does this seem normal ? or might I have a problem with the motor? Ideas?
Stock Bore
No Port modifications.
K&N with Lid Removed

 

The bigger pipes don't work all that well with stock set ups. I assume you re-jetted for the pipe change. The best thing to do now is start thinking about other mods to go with the big pipe. Carb, reeds, porting, and head work.

 

Mine is equipped a little differently, but the (Paul Turner) pipe on mine has excellent low end power. I would say spend a little time with your carb, play with needle position/main jet size. You might also look at your power valve window, and goose the throttle in nuetral and see if the arm moves. Sometimes they can stick in the open position and make your bottom end go kaput.

I have 170 psi, 39PWK carb, reeds, no airbox so I'm set up a little different but I still think you should have good bottom end with that Fatty.

 

Check your jetting, I had a FMF pipe/silencer on mine before I sold it and the low end ripped. Keep an eyes on your powervalve too, make sure the bearings aren't shot in that. That was my problem with mine. When I fixed that a made a HUGE differance.

chuck

 

Thanks for all the good advice. I checked the Power valve, it's good. What I have not done is rejet after putting on the new pipe !!duh!! I also started to run a more oil rich fuel mixture on this past trip. That would make it a bit more lean. Also cleaned the filter just prior to the trip. That would also make it a bit more lean. Also changed the silencer from the "Turbine Core" I typically run to the "Power Core" I think the "Power Core" is a bit less restrictive == more lean. Guess What!! the low - mid range felt like it was running waaay lean, the pipe started to discolor "BLUE", and I blew out some radiator fluid while riding. All signs I was too lean. I was lucky I didn't blow the motor. I was so busy having fun with the new Top End power that I didn't stop to think about the source of the Bottom end loss of power. I'll need to spend some time with carb this weekend.

Thanks Again