Hi, Im really pulling my hair out now.

I have a CBR400 NC29 and its a moody bitch.

Starts first time, revs nice up to 4000 rpm starts to gargle and sound 'chokey' past here under no load.

Under load it will not pull properly past 4000. up to this its sweet as a nut but past its just awful.

I have cleaned to carbs numerous times. no better. a have 3 sets none better than the other i also have three throttle position sensors but its the same with each.

The bike has a K&N filter and Scorpion end can

It had originally been jetted up to 116's

i put standard 108's in, it went worse.

i put some 122's i had and seems slightly better but still very poorly and this seems a too big a jump up from standard.

Any help would be great.
Thanks Guys/Girls

 

Check the timing, how's compression? Kinda grasping at straws, it's usually a carb
issue. Sounds like you've covered that end of the problem.

Fuel, air and spark, all delivered at the right moment in the right quanitys.

It's of the era, where Honda was screwing everyone with a cheap R/R. You might
check that and the connectors for 'heat-sign'. Burnt/cracked/melted, etc. Could be the spark is the failure point.

That's my best guess, hope it helps, Ern

 

P.S. Check for exhaust leaks, as well. That can have an effect.

Ern

 

Sounds like a main jet is plugged. Your pilots appear to be working but around 3500-4000, the main jets start to take over.