CF650 flat spot? on 2800-3000RPM

I have had like flat spot in about 2800-3000RPM it works smooth under that and over that. but if I hit that magic rev zone bike will start to stumble/sputtering.. it feels like.. hell not sure.. if you rev fast from idle to higher RPM range its ok.

If I just rev engine and try to hold it 3000rpm you can clearly hear exhaust making sputtering noises.

but it's not stick coils as I did try different ones already,cleaned the tank pump.. lots of rust btw... :/

It also has new fuel inside (as I did run it empty by accident, if bike can't hold idle.. do check before taking tank off that there is fuel in the tank.. :lol8: )



This problem has been already long time and really start to annoy me only if I am in traffic and have to hold that speed :) really hate that sound and jerkiness of the bike at that moment.

I've always found rev range to be snatchy and not so great in that area, but yours sounds more pronounced, dirty injectors? Dirty air filter? Tried new plugs? Tried higher octane fuel? Just guessing.....but that rev range does feel better in every gear than 1st, 1st gear being pretty snatchy, but these fuelling woes are hardly restricted to our bikes, nearly every other euro3 bike onwards has similar issues.

It has new air filter already, plugs i haven't change yet.
Normally I use 91 (get from any station) 95 I have tried but it worked the same.

I have run injector cleaner but this was while back.. might try it again.

as i just came back from ride it does feel like one cylinder would be missing. this could be from spark but at the very specific RPM range??

Try NGK Iridium plugs, maybe injector cleaner and 95 octane. Can't guarantee, but maybe....:icon10: Also Asian fuel is high in water and ethanol, don't trust the numbers. :rolleyes1:

I have already Iridium.. Not NGK cos when i bought them they only had Denso.. :thumbsup:
but this is about 7000km ago..

Tell me about it!! I try only fill it up at my local gas station where I never had problems.. unlike one time when I did venture unknown station and decided to fill up 95... bad idea !! Had to empty gas tank as that fuel was full of some Sh**!!

As you ran the tank empty, you probably sucked all dirt into your system.
Forums are full of this situation, not only bikes.

Clean or replace the fuel filter first.
If it does not help, and the injector cleaner doesn't help as well, you might be in for some professional cleaning of the injectors.

The symptoms you are describing are the same I had ages ago with my 1975 BMW, when there was water in the carburators (I never found out how it got in sometimes after wshing the bike, but never when driving in hte rain). Maybe some water ended up in your gasoline tank causing the problems.

Could be bad fuel ? I came to this thread thinking I had the solution... hahaha I thought you meant flat spots on tires.

I don't think its water in the fuel as i have change fuel completely and this problem has been longer than I run out of fuel.

already took fuel pump out of the tank and cleaned its filter, will try to replace second fuel filter or just take it out completely.

There is a change that this was small air leak, as I did tight throttle body lower screws.. if air leak is not there it might be in in butterfly valves shafts o rings that are leaking.

It was super good today, enjoyed riding.. even in the city.