3500 rpm flat spot?

[jfwilliams23]

I have rode motocross all my life. I recently bought my first street bike, a 97 Katana 750 with 11k miles. The bike has to be choked slightly to get started and takes a while to warm up, I think I can fix this with a washer on the needle or an adjustable needle. My main problem is a flat spot between 3500 and 4200 rpm, after that it pulls really strong, I'm not really familiar with this type of carb and was wondering if it was a jetting issue. It has a 4 into 1 slip on under it and a Honda silencer?? (I'm not sure how that happened, it was like that when I got it). I am also checking the compression this evening and changing plugs, if there are any suggesttions on the best plugs. Any insight on this bike is greatly appreciated.

[Kila-Beave]

If the 750 is like the 600, 4k is when the main needles should start to move and let the main jets start working. I had a similar flat spot stock and an Ivan's jet kit cured it.

[jfwilliams23]

Thanks, I thought that would be the case, but experience is better than a hunch.

[DumbLuck]

a very good cleaning never hurts either. with a 4-1 exhaust it might already be jetted. a 5* advancer is a simple upgrade too

[md86]

Shimming the needles won't help warm-up time . But it MAY help the low/mid rpm weakness ....
Best plugs are stock plugs . NGK JR9C .
Has the bike been jetted ? Check it out . Many just turn screwdrivers and hope for the best . Also look at the bottom of the slides to see if they've been drilled/tapped . I had to fill mine in and re-drill them the right size because of the aforementioned .

[scottynoface]

If I were a betting man, I'd say the owner took the jet kit out of the bike and sold it seperately before you bought the bike from him.

[whitecl0ver]

take the K&N out and install factory AF

[jfwilliams23]

Don't have a K&N,,,, Do have an AR-15 (and others) though, and I agree.