szr660(xt660) running problems

I just found this forum when the post below popped up on google. I'm having a similar problem, and thought you may be able to help!

http://www.yamahaclub.com/forums/index.php...9&hl=szr660

I bought an SZR660 with 5k miles on the clock 6 months ago which had been standing for a while. The previous owner had replaced the battery and got it running.

The bike came with a k&n air filter and renegade straight through exhaust. When I first got it there was a massive flat spot in the midrange which the bike would struggle to pull through on full throttle, and the fueling felt out everywhere. If the throttle was opened quickly the bike would bog down like hitting the rev limiter.

I stripped and cleaned the carbs,but the only thing I found was a little fluff in the choke mechanism. While I had them apart I also lowered the clip on the CV carb main jet needle one notch. This didn't really help so I put it back to stock.

As part of a service on the bike I adjusted the valve clearances as a couple of the inlets were tight. This made a massive difference, and the bike ran much better, although it started popping and banging from the exhaust on a partially closed throttle (not necessarily a bad thing! )

The petrol mileage also improved slightly.

As I have a 102db limit track day at brands on thursday (05/05/08) I purchased a standard can, but after fitting it the midrange flat spot is back with a vengeance! This is a nightmare as it's my first track day and the last thing I need is a bike that doesn't run properly.

I will be fitting a standard air filter in the hope that it sorts the problem out, but would appreciate any advice as I'm not especially confident it will.

Thanks,

David