Hello all!
I recently bought myself a very clean CBR 600fx, I haven't done a major dig into the bike as of yet however a small inspection has discovered the bike is fitted with a K&N air filter( will probably replace with paper), what I assume to be the original downpipes although I'm not 100 percent sure, aftermarket link pipe with a 350mm delkevic oval muffler, fuel lines look to be replacements and relatively new, fuel filter is yellowish, for the price I'll replace it at some point along with plugs, oil filter and general service. The bike does have a flat spot around 9k which lasts until around 10k in all but 1st gear however gear ratio could be masking it I guess, so far I'm chalking it up to the K&N filter, has anyone had any similar experiences with a flat spot so high up in the revs and have any other tips and ideas, carburetion everywhere else including idling seems absolutely spot on!
Any help, tips and tricks would be massively appreciated and I can't wait to maybe help out and contribute on some other posts!
Thanks,
Adie

 

Greetings & Salutations!!!

Most likely carbs are dirty. Best to do full restoration job with complete disassembly, ultrasonic soaking, micro soda-blasting. Otherwise, you'll be pulling carbs 3-4 times for ever deeper cleaning. I know one guy that had to pull carbs 10x before he got them clean enough. So I recommend full job 1st time around.

 

Thanks for the quick reply!! Just seems really odd that it seems to be that 9-10k spot that's the issue, also do the factory pipes have the cross over between 1-2 and 3-4 as the pipes on my bike seem to be a single unit but don't have the cross over.
Kind Regards,
Adie

 

Crossover improves mid-range flow and torque.

Without it, you have less flow and too-rich AFR in mid-range.

Best to check AFR with wideband-O2 or dyno.

Try finding factory pipe and put it back on.

 

The 9-10k spot is certainly a strange one that I have not heard of before, normally 4-5k, They are certainly aftermarket headers if they do not have the link pipes. Probably Delkevik as well.
Early on they used to put the link pipes in but then removed them (obviously cost driven) I queried this with them a number of years ago and they stated that in their testing it did not make any difference.... I would have though Mr Honda would have been through this and would not have put them there if it did not make a difference.
Good luck trying to find a good used set if you go down that route as we all know to our cost that our winters destroy the mild steel pipes alarmingly.