Last season my carbs were troubling me with suddenly running to rich then running fine. Then going rich, then going fine.
First a few checks. Do fuellines have the standard length and diameter and are they correctly routed without kinks?
Any inline fuelfilters present that may hinder fuelflow? Remove them, you don't need them. It's a known cause for poor fuel delivery. Some are lucky however.
Tank ventilation in order?
Sometimes floatvalve needles stick on and off. An additive like Tunap or Forté can work miracles.
I've bought a rebuild kit for all 4 now
Most probably you won't need it and if it is an aftermarket brand like Keyster, I'd stick to the original brassware that hardly wears if at all. That's no wonder btw, if you realise how little gas has passed all in all in just a 400cc motor with no less than 4 carbs.
The only thing i cant figure out / google / find on this forum. Is the size of the jets i should be using on my setup. It is a stock CB400F with the marshall deeptone exhaust. (no pods, just the old airbox).
Stick to original size*. Back then Marshall advertised that no rejetting was required.
hence its probably the float system that is worn?
I doubt it, I'd start with the above checks. Just replacing things without diagnose will not learn you anything.
Your carbs are pretty easy to work on. If I were you, I wouldn't separate them from the rack. I would only remove the float bowls and you'll have access to practically all brassware. Clogged or partially clogged slow jets often occur and slow jets openings on your model are very small indeed. After removing the main jets (are those tiny O-rings still Ok and do they seal well?) raise the slides to full open (just imitate full throttle) and you can get the needle jets out from underneath. Either they drop by themselves or they need a little help by inserting a wooden toothpick or something from underneath. You can then wiggle them out. Carefully inspect all jets, slow jets in particular. If necessary you can clean them with stranded copper wire.I wouldn't mess with the needles and I wouldn't mess with the floattangs to 'adjust' the float level. Checking is fine, but think twice before you change something. Most probably no one has ever touched them, so they should be OK. What you could do however, is polish very lightly the float swivel pins so they'll allow smooth movement of the floats. Remember: ultrasonic is no guarantee.
* The CB400F parts list lists no less than three different sizes for both slow and main jets. Consult:
http://www.honda4fun.com/pdf_parts_list/pdf_spac400/CB400F-F1-F2/CB400F-F1-F2.pdf
