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By Graham43
#84280
May seem an obvious answer to my question but I would just like to put it on the forum in case someone has some thoughts about this problem. At times, not always, when I turn on the fuel it floods out of the bottom of the float bowl. Correct me if I am wrong but the brass overflow tube in the float bowl empties out of the small tube cast into the bottom of the float bowl and is not controlled by the float bowl grub screw used to drain the float bowl? Correct? Therefore it must be the float valve leaking? So why is this worse after the bike has stood a while - small leak from the float valve? Is this a common problem possible due to the float not having the strength to close the valve properly? Can this be adjusted to make the float press harder on the valve?
Any thoughts?
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By Wheaters
#84281
The only way to know is to strip the carb and have a look. Check the float itself is working properly (no fuel in it, all intact, especially in the area around the pivot/hinge point and moving freely, not sticking).

If all is OK with that, the float needle and seat probably need renewing.
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By stinkwheel
#84284
Might just be the float "sticking" open too if it's been sat open for a while. When it's leaking, try giving the float bowl a couple of sharp rap with a piece of wood and see if it stops.

Shouldn't happen with a 2005 mikuni but I'd had older (pre 2000) Japanese carbs on other bikes suffer from furring/corrosion on the alloy needle valve which caused it to stick in the channel (both open and closed). I put this down to damage from ethanol in the fuel. This was cured by fitting a more recent, viton-tipped needle valve.

I've also had a situation where the tiny sprung "pin" in the top of the needle valve has stuck in, again I supect due to a period of disuse and/or ethanol damage, this would have the effect of increasing the float height by a couple of mm. Not sure if your needle valve is of this type but it's very common. A squirt of WD40 and a wiggle up and down of the pin usually fixes that one.

In both cases, the answer is still almost certainly to visually inspect and clean the float bowl and needle valve componants and replace/repair anything that looks damaged.

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