STILL MISFIRES

I've got a 98 t'cat 24000 miles started misfiring at 7500 rpm form hot or cold (all the time runs fine upto 7500)flames and pops from exhaust at constant rate above 7500.



I've tried -



tried new fuel and redex

new spark plugs

changed the coils

checked the engine timing



still mifires?



feels like fuel is getting into the exhaust and ignighting (exhaust gets really hot quick)



poss a valve not openen/closing when it should? but why does it only happen at 7500 rpm?



cdi fails at 7500 rpm?





any help appricated Phil

clean the carbs?

I agree the first thing I'd look for is a partial blockage somewhere in the fuel system, leading to starvation at higher revs. Could be one of the main jets in the carbs, or the fuel feed generally - blocked filter? dodgy pump? petrol tap partially closed or blocked? fuel hose collapsed? - lots of possibilities, some sillier than others.

IMHO Redex, and many other so-called "carb-cleaning" additives, are a waste of time. The only one that's worth using is the Silkolene stuff (HST?) that works to prevent carb icing, and even that won't necessarily clear out a blocked jet. I've taken to filling up with 97-98 octane stuff (Shell V-Power etc.) every now and then to keep everything clean, and stop the carbs getting clagged up if the bike's left unused for a few weeks.