SOHC.co.uk Forums > CB350/400

carb cleaing

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59viperman:
 :D after having bother with the carbs on my 77 four I was wondering if anyone on here does cleaning ? they set up well but then start pissing petrol out of a couple of overflows, it had stood for a good while before I got round to it so I think a good clean will sort a lot of problems.

PatM:
In my humble opinion- if you have carb-cleaned them and blown them out with air compressor- then further cleaning will probably only enhance their appearance. My carbs used to piss fuel when I first installed them- but after a few taps on the float-chambers and regular use of the bike- they don't leak any more and the bike runs sweet. I was always on a tight-budget when I brought my 400, so I couldn't afford to have them cleaned ultra-sonically and to be honest, Id rather do any job myself- then Ive no one else to blame.
Just my thoughts..

Lobo:
Surely there is no point whatsoever giving yourself the grief of a carb strip down to cure any overflow! There can only be one issue in this case.... a stuck float, which as Pat said, is cured by a gentle tap on the bowl. (a bad float valve would drip versus 'piss petrol'). My 400F does this too, despite a full carb strip-down, deep clean & meticulous rebuild. It runs sweet as can be, but overflows at fuel on each start I get back to it. (and to be honest, no taps required, just the movement / vibration of starting seems to stop my overflowings)
And I reckon there's the point, if she's left standing any amount of time I get this problem, but after 1st start / run its all cured until next time I go's away. (750K2 does it too, but not to same extent).  Fix in my case is to use the bike regularly....

A question to someone out there.... is the fuel evaporating within the chamber / leaving a sticky residue perhaps the issue... and if so is there any petrol additive which might solve the sticking float problem?

PatM:
Hi- on the subject of card rebuilds and aftercare- my efforts were:-

-Clean outer with carb cleaner and toothbrush- don't fret, I used the wifes and out it back when I was finished!
-dismantle float chamber, remove all jets and DISGUARD.
-Remove Needle through the top- undoing and tag-bending, dropping spacer, scouring garage floor with magnet...
-I don't break the rack of Four...
-Thoroughly soak with carb cleaner.
- Clean all the float assembly- again, with carb cleaner/toothbrush
-Blow out every hole/orifice with air-line (you need an air-compressor and attachments to do this- an tyre inflators not up to it as you really need to be delivering a decent rate of air at about 40psi continuously
-allow to dry.
-carefully rebuild each carb with new jets, seals and float valves
- set float heights if nec- but whats essential here is that the floats are shutting the flow off- I blow down the delivery hose- not v hygienic, but proves the point. I also use a tiny spot of Vaseline when Im butting any new seal into place for the first time- to allow it to seat properly.
- Fit the float bowls
-fit carbs
-fill with fuel
-tap with end of hammer- shaft- if overfills

as for any additive to prevent varnish forming- Id suggest if laying bike up for a long period- drain floats. Any addition to the tank would need to be anti-petrol, so to speak- be likely to contain ethanol and risk dissolving seals and making bike run like a dragster!

I remember my brothers BN 400/f used to sometimes overflow- We all used to turn our fuel taps off when arriving at Pub to stop this. Generally, I find turning tap of unnecessary but do it when I lay bike up for a couple of weeks.

Clem2112:
I wonder if ultrasonic cleaning might just dislodge one of the blanking plugs/pellets ?

Found that the Keyster valves were worse so took the advice of others and used sime metal polish to "gently" clean up to float needle and valve seat.... No piddling carbs since.

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