Carb fitted, fuel coming out on start up

Reinstalled standard cleaned carb and fuel is pouring out of the top hose when I turn the starter that seems to be the overflow one or should it be connected somewhere. Anyone got a pic or diagram of the way all the pipes connect up and where to?

Here how I refitted...


You have a float valve that is not shutting off for whatever reason.  For fuel to come out the vent hose, the fuel level is VERY high.  You have a severe flooding condition.  Must be corrected immediately.

Ok, before I take the carb back off its nothing to do with...

Fuel cap wasn't on or

Any leaks around the carb rubbers etc?

Also,I put a washer on each of the float bowl screws that I replaced with Allen screws; would this mean the gasket isn't pulled up tight enough- should I take these off and reassemble without the washers?

Just trying to attempt the easier stuff before taking the carb to pieces....

No to all your questions.  The problem is internal. There are quite a few possible reasons to the float valve to not shut off.  Sometimes the valve will stick just because the float was down so far with no fuel.  The very easiest thing is to turn the gas on an tap lightly on the float bowl and see if the flooding stops.  But most likely you will have to take the carb off and look inside.


Did you adjust the float setting?

Did you remove the float valve seat?

Did you replace the float valve seat O ring?

Nothing touched as far as I'm aware, just sent for cleaning and reinstalled on bike.

Looks like carb off again....I'll try the tap first

Ahh - always new and significant information not originally presented.  You did not work on the carb, somebody else did.  So anything out of sight is a mystery.

I assume that I've not got fuel in the engine oil from the fuelling problem? seem to remember something about it somewhere or it may have been a 'prime' fuel petcock problem?



Change the oil cheap insurance. Please take the "assume" out of any equation. Well cheaper than engine rebuild. one of the first things I did for my scooter was to change the vacuum petcock to manual one.

Tapping didn't work so carb back off. Float looks to be moving freely so will reinstall and see again. Getting familiar with taking carb off.......applying heat with hairdryer very effective

Also checked diaphragm, gaskets and tiny o ring, seem all ok...

With a little bit of ingenuity you can connect a fuel hose to the carb and see if it floods without installing it on the motor.  Remember, the flooding is fuel getting past the float valve, nothing else.  The seat to body joint could be leaking,  the needle valve could be leaking,  dirt or other foreign material could be stopping the valve from closing, the float level could be set wrong, float installed up side down (probably not but possible on some carbs), wrong parts...........   Whatever the problem is, it is related to the float valve.


Were any new parts installed when the carb was "rebuilt"?

No new parts installed during cleaning..

Update....latest installation had fuel coming out.

Removed again, float bowl off and gasket buggered. New one deliverd today for future fitment. Watch this space....

Relate to the answer "no parts replaced".  I recommend the brass float valve seat be removed and the O ring on the brass valve be replaced OR the valve assembly be replaced,  The rubber tip of the float needle can look fine but still be bad so if just a new O ring does not solve the problem then replace the valve seat assembly.


Also when adjusting the float height, be aware the float needs to contact the spring loaded tip of the needle but no depress the spring loaded tip.  To do this it often requires the carb be held in a position that the weight of the float does not bear on the needle.

Ok, bike now able to rev freely in neutral on test, but carb leaking looks like from the float bowl. New gasket fitted down there so could be misplaced, or maybe due to me using different hex bolts in place of the original chewed up screws? I left off the bracket for the idle adjustment knurled knob as the hex bolt wasn't bottoming to enable me to get a tight feel, is that related? Is this bracket part of the problem...does it need to be on a specific (longer) bolt ( looks like it as the only seems to be one within reach of the bracket). Should I tighten the bolts on the float bowl in any order as I usually go diagonally.

So nearly there.....

Not sure I understand the problem.  The screws holding the bowl on need to be the correct length.  Too long and they will bottom the threads an not clamp the bowl.  Too short and you risk stripping out the threads in the carb body.  Original screws are Phillips drive.  Replacements are usually socket head cap screws (Allen head screws).  Match the lengths with the old screws.  Tightening order is not very critical.

Parts list shows 3 screws of one part number and 1 screw of a different part number for the wire bracket for the idle adjuster.  So yes, it looks like the screw for the bracket is longer.  I do not know the lengths, you will have to compare to the original screws.  Socket head cap screws will work fine.  You can always add some washers to a screw that is a little too long.  The screws need to clamp the bowl to the body but do not need to be excessively tight.  Tighten snug like you would with a screwdriver.

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