SOHC.co.uk Forums > CB350/400

Starting Mystery

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exvalvesetdabbler:
A thin cocktail stick with cotton wool wrapped around the end to make a skinny cotton swab does work well to clean up the float valve seat with a minimum amount of metal polish.  It's usually the ridge worn into the pointy end of the float needle that spells trouble.

I wish you could get the float needles with a viton tip like Ford used in their carbs.


Dave

DomP:
I managed to find viton tipped float needles for my xs650 that were intended for another bike entirely, often wondered if you could get them for cb's

Seabeowner:
My CB550 came with a mix of float needles, a couple are rubber tipped (probably not viton but they have caused no issues) so I am sure they are available.

Otis:

--- Quote from: K2-K6 on November 25, 2025, 02:59:31 PM ---The ignition isn't common to 3/4 and so has half-a coil, point etc involved in each .... suggesting they are ok up the line.

I've had plug caps give similar to this for individual items before. Dead cylinder at cold, chiming in when running, to ultimately run ok when all up to temp. One of those was a disconnect from HT lead in top of cap. Jumping across effectively when it got going. Took some time to find that  :)

Possible to swap #1 & 4 leads over  ? (Enough length available  ? ) to give functionality check either much work.

Start it in the dark, then look for "tracking" sparks around caps snd HT leads on 3 & 4 that may give you indication of leak that is improved by heat etc.


--- End quote ---

I don't wish to speak too soon but have just been tinkering along the lines outlined above. Regrettably leads 1&4 were not interchangeable as that was a good starting point. However, I thought it worth checking the cap connections to the leads and found that the two problem cylinder leads could be tightened by a good half to three quarter turn; the other two were sound. I thought, give it a try and to my amazement she fired up up and all downpipes got hot simultaneously.

I'm really hoping that this was a simple fix although I guess it won't do any harm to replace the leads and caps in due course.

Thanks again for the tips and advice given.

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