SOHC.co.uk Forums > CB500/550
CB550 Tuning Advice
Neilw:
--- Quote from: deltarider on October 20, 2026, 10:51:03 AM ---In general: do not position an auxiliary tank much higher than the bike's own tank. This to prevent floatvalves opening and as a consequence carbs overflowing.
--- End quote ---
Got that; tried to keep the differential the same.
Got the float heights about right; fuel is settling a few mm below where the float bowl joins the body of the carb.
I've double-checked the drain screws for debris and cleaned them with carb cleaner and compressed air.
Also flushed the carbs through with petrol, and for the most part the fuel is clear. I flushed about a litre of petrol through; there may be two really tiny black bits, which you can barely see with the naked eye. It's as good as I can get it, so accept that perfect doesn't exist, and there will be natural contaminants in fuel that I can't do anything about, but I'm not going to put a filter in at this stage, as the bike as standard didn't have one. Might be a different story when I get to the Tank.
OK, back to bench syncing and sticking them on the bike.
McCabe-Thiele (Ted):
It's ironic, when I first started my 500 it ran great, I had treated myself to a new auxillary petrol tank that came with a T piece and pipe.
A few days later just before I was going to fit the tank I started it up again, iirc the pipe had swollen and was a bit sticky to the touch. When I started the engine it ran like a camel and started flooding.
There were black bits off the inside of the pipe in all the bowls. I was so gutted I walked away for a few weeks before I could find the motivation to take the carbs off to strip & clean them again.
That's why I added the Aeroline filters, yes they are not original, they are pretty well hidden under the carbs, you have to look to notice them. I just figured an old bike needs some extra help, probably ott, peace of mind.
When you eventually fix the problem anf post the cause/fix it will be satisfying, sharing here helps us all.
badger_eng:
From my experience of using the auxiliary tanks that are cheap as chips from all the usual places, the tubing that comes with them is very poor quality. I have my doubts that the tubing is even fuel compatible.
After using the cheap aux tank for my first resto 5 years ago, the tubing had perished within a year.
I replaced with cheap clear polyflo style tubing. Whilst this quickly goes hard / brittle, it does not shed its guts into the carbs like the ‘’rubber’’ variants do.
deltarider:
It's another advantage of my simple method for checking the fuel levels: by draining the bowls you'll detect any contaminants rightaway. http://forums.sohc4.net/index.php/topic,185754.msg2151647.html#msg2151647.
scottly:
--- Quote from: Neilw on October 20, 2026, 08:18:36 AM ---
--- Quote from: K2-K6 on October 20, 2026, 07:55:32 AM ---
--- Quote from: scottly on October 20, 2026, 12:45:15 AM ---Could the rubber bits be coming from the rubber sealing washer inside the petcock?
--- End quote ---
On the auxiliary tank fuel supply ?
I don't know what config is there, but running some fuel i to clear container should show anything not desirable.
--- End quote ---
I'm using a clear auxiliary tank with a clear pipe.
--- End quote ---
Sorry, I missed that an auxiliary tank was being used. I was thinking of the petcock in the stock tank. :-[
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