I own a CBR400 (NC29) which appears to me to be running lean, the bike is lethargic above 8K in gears 4-6 generally. The bike had previously restrictor discs in the carbs, I assume the jets may also have been changed to suit?

Either way I wish to check the main jets and possibly change them. I have done this once before on an old car which was very easy. However on a bike with 4 carbs it's not something I wish to tackle unless it's something someone says is easy to do (already had an easy comment on the general section), appreciate the positivity CMSMJ1, but forgot there was a workshop section for this sort of query.

If anyone could go through how it's done or show me a your tube clip I would really be grateful. Can the carbs remain in situ?

Regards,

Cosy

You need to remove the carbs to do this.

There's a DIY sticky in the V4 section, although the carbs look a bit different the process is the same.

viewforum.php?f=24

Removal and installation of the carbs for the first time will take longer than rejetting them.

Thank you for that, it was a great help and now fixed. Found it was over fuelling due to a loose emulsion jet on number four.

Good work.