650 flat spot

[artgwebb]

Morning all

Just bought a really nice 650 - yes, another one... It's very sweet up to 5100rpm but has a flat spot/misfire from here until around 5400rpm. thereafter it pulls well but doesn't feel as sweet as it should. I'm concearned it might be running too lean above this flatspot band and possibly detonating, and that I'm not hearing it with the ambient noise at this rpm) I suspect incorrect needle positions and/or worn needles, but before I go tearing it down, I wondered if anyone else has experienced similar problems. As it seems to be the easiest thing to do, I'm going to swap black boxes first, though my gut feeling is that it's fuel delivery

Anyone got any ideas?

Gavin
Scotland

[Tusk]

I had this on my 88 for a long time. The problem was (bare with me):
First I put in a Factory Stage 1 jet kit (stock air box - Supertrapp exhaust with around 8 discs)
Then I took off the stock box and put on K&N pods.
Problem arose! A bit of a stumble around 4500 to 5K I believe.

After -well- many years I finally broke down and fixed it. I installed a Factory Stage 3 kit and WOW... stumble gone and power delivery across the board is better and smoother.

So, what (if any) mods might be on this Stumbler?