Katana Owners Club U.K.

Just been changing the oil/filter and try to stop the blowing exhaust issue that surfaced at Mankee. Anyhow I noticed that the exhaust on 1&4 were sooty and 2&3 white . I’d expect the middle cylinders to run a bit hotter but the difference was really noticeable. Any potential issues I should be checking out? Cheers

A few possible reasons ,
Coil , only because it's 1&4 and2&3. Just swap over see if issue moves. Not too likely.
Blowing exhaust altering settings ....possible not too likely.
Float heights .......possible
Mixture screws not set the same for outer and inner........if the plugs are white white may vey well drop a valve....but if reddy white it's ok.
Not jetted for the exhaust you have ....kinda covered by all the above carb points .
For me if the white isn't white white and the bike runs ok , put in new plugs as part of service and run it with plug checks after a run just to monitor.

Had a similar thing with my bike when I was chasing fuel problems. I inadvertently left the vacuum tube off no2 carb (fuel tap on prime) and went for a test run, strangely cylinders plugs 1&2 where very lean yet 3&4 where still sooty?
It was a very short run only a mile or so so no damage was done and new plugs where fitted before the run.
Maybe worth checking?

try taking the ht caps off and clipping a quarter inch off the lead before refitting. if the coils permit the same then do that end too. in fact, if you can remove the ht lead from the coil, if its even remotely brittle, bin them and get a new set. as normal, check your earths too. it might be just a tiny misfire that you arent even noticing.