My mate's got a cbr 600 and has'nt been used for a while , he's just put it back on the road and at 4 to 5000rpm holds back and splutters then clears, then again at about 9000 rpm , any ideas ? plugs been changed , thinking that a coil pack could be breaking down as it's ok just revving it , only does it when loaded .

Air box / filter in or connected etc?

Hondas are known for week reg / rects, although that would normally mainifest itself as problem from 5-6k upwards, not clear again until 9k. Worth a look though.

If it has been standing then perhaps the petrol has gone a bit manky in the float bowls (assuming it's carbed!). Any bike that's been standing a while it's worth giving them a blast out.

What age of bike is it??

Sounds like a fuel blockage problem,, if they are not used you can get gumming up of the fuel system, is it on carbs?

If it has been standing then perhaps the petrol has gone a bit manky in the float bowls (assuming it's carbed!). Any bike that's been standing a while it's worth giving them a blast out.



Ditto this, had this when I bought a Blade that had been laid up, unused unleaded turns to a 'varnish' type lawer in the floatbowls and jets - then breaks up into flakes causing fueling problems, this would be after the fuel filter so a new filter won't cure it.

Drop the floatbowls, clean then & the jets (may need to replace jets if too bad).

He said the fuel has been replaced and the carbs taken off and cleaned , dont know about the jets . Heard it the other day as he was going and it sounded like a missfire as he was just starting off , only does it under load .

If the carbs have been done already then next step is coil & HT leads, then Regulator / Rectifier I'd say.

Something like this can be a real PITA to trace down!!

Said to him to disconnect one coil and start it , although will run really bad on two cylinders , then swop over and start it on the other coil and see which is worse , as i suspect one of the coils is producing a weak spark , so if wont start on one at all that may be the coil thats had it .

i had a CBR6 with a problem like this, it turned out to be a split exhaust can (std) it just wouldn't run correctly under 9k but would idle fine, went like stink over 9k mind you :D