SOHC.co.uk Forums > CB350/400

Fuel tap causing flooding?

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Seabeowner:
Strange, the pressure when there is no flow will be the same as it's the height of the fuel in the tank to the needle valves in the carbs that determines the pressure. When there is flow there will be a change dependent on restrictions in the path. But the needle valves should be strong enough to hold back pressure from a tank filled to the brim. (but in practice they often drip a tiny bit, so always turn it off)

TrickyMicky:
The floats and float valves will do their job irrespective of what position the fuel tap is in, the fuel can only pass down through the same delivery pipe.  Is there a chance that the tap is actually leaking in that position, and gravity is allowing the fuel to run down the outside of the pipe, running over the outside of the carbs, and following the easiest path downwards which would be via the overflow pipes.  Make sure everything is bone dry, kneel down next to the bike, then using a torch,(NOT A MATCH!!), turn on the fuel and see if the outside of the delivery pipe becomes wet and shiny. Have fun, we love this hobby don't we?  Late PS:-  I meant to say that it really does sound as though the tap has been wrongly assembled. There's an exploded parts diagram on the CMSNL website, might possibly help.

Athame57:
I think I would be looking for a new tap myself by now!

350Simon:

--- Quote from: TrickyMicky on August 07, 2022, 08:03:24 PM ---The floats and float valves will do their job irrespective of what position the fuel tap is in, the fuel can only pass down through the same delivery pipe.  Is there a chance that the tap is actually leaking in that position, and gravity is allowing the fuel to run down the outside of the pipe, running over the outside of the carbs, and following the easiest path downwards which would be via the overflow pipes.  Make sure everything is bone dry, kneel down next to the bike, then using a torch,(NOT A MATCH!!), turn on the fuel and see if the outside of the delivery pipe becomes wet and shiny. Have fun, we love this hobby don't we?  Late PS:-  I meant to say that it really does sound as though the tap has been wrongly assembled. There's an exploded parts diagram on the CMSNL website, might possibly help.

--- End quote ---

This seems like the most plausible answer to this conundrum. I shall try tonight when I get home and see what happens, a leak at the tap crossed my mind but I just imagined it would drip down onto the crank cases and so dismissed the idea but as you say the fuel may well be flowing down the outside of the feed pipe!

Ta

350Simon:

--- Quote from: Athame57 on August 08, 2022, 09:01:33 PM ---I think I would be looking for a new tap myself by now!

--- End quote ---

I don't really want a shiny new tap as my bike is nicely aged apart from the exhaust which will tarnish fairly soon anyway. If anything I'll try and rebuild the old tap I think.

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