Vibrations above 4.5k rpm in neutral/all gears

[MetModMan]

Hello friends,

Recently picked up a 2006 Ninja 250r with ~25k miles. It wasn’t well maintained by previous owners. Ended up replacing the carbs, rebuilding the petcock, adding an inline fuel filter, a new air filter, and putting in new plugs to get it riding again. Adjusted the valves to keep it running for more than about 10-15 minutes.

Started having problems with really bad vibrations starting around 4.5k rpms that just get worse with higher rpms. I think they might have started after dropping the bike after stalling in 1st gear when parking. The vibrations happen in neutral in the driveway and in all gears when riding.
I’ve tried:
-carb sync x2
-replacing the plugs again (one went out of spec - gap too small)
-adjusting the valves again (two went out of spec, but this might have been because I didn’t have a torque wrench the first time)
-reinstalling and retorquing the engine mount bolts
-replacing the cam chain tensioner
-replacing both muffler gaskets
-adding an extra nut to both muffler clamps (kept getting loose on the right side)
-tightened the kickstand nuts (were loose)
-oil and oil filter change

None of these things have helped, and it seems that the vibrations may be getting worse the more that I ride. Is there anything else worth checking here? Or is it time for the shop/replacing the engine?

Thanks

[Triple Jim]

Originally Posted by MetModMan

-replacing the plugs again (one went out of spec - gap too small)

Are there any unusual sounds? My experience with self-closing spark plugs is that they can be caused by serious internal engine problems. In my case it was a failed connecting rod bearing that was letting the piston travel too far!

Welcome to the board, MetModMan!