my carb over flows

[ae173]

any ideas guys and gals,
i have a two stroke carb that keeps overflowing and tried the usual ie, carb level, float and dog work fine but still overflows, no air leaks, bought new carb and still over flows, ready to get out the matches lol, could it be the flow of fuel ????

[TonyRPH]

Sounds like excessive fuel pressure overwhelming the float valve.

Do you have an electronic fuel pump feeding it?

If so, try fitting a pressure regulator.

[ae173]

its just direct feed from tank and only tap and filter inline but i would of put it down to fuel preasure aswell, but where from, unless the tap is knackered!!!

[littlebasher]

Does the float have a hole in it?

[Tunku]

Missing/worn float needle? Was it a complete replacement carb? is the float chamber upside down?

[TonyRPH]

He said he bought a new carb, so can't be float.

OP - is there any kind of vent to the float chamber?

Is this vent blocked, or getting vacuum from somewhere?

[ae173]

float dosnt have a hole in it and the carb came complete, propa miffed on this after 20yrs of working on these two strokes never had a problem like this one

[Globs]

ae173 said:

unless the tap is knackered!!!

Have you checked the tap?

[Huntsman]

Blow into the banjo where the fuel pipe goes, keep blowing and turn it upside down, can you still blow in?

Flot should flop down when you invert it and then you shouldn't be able to blow.

[ae173]

the carb has two vents which both have bung stops on them as standard, im still thinking it could be the tap alowing too much petrol through

[TonyRPH]

ae173 said:

the carb has two vents which both have bung stops on them as standard, im still thinking it could be the tap alowing too much petrol through

Is this on a bike?

I remember once having problems where if the tap was switched to reserve, the carb could flood. (Old Yamaha 50cc IIRC 1970's)

Cured by only using the reserve position when needed.

But this shouldn't happen as a rule, because surely the tap is only just that - an on off valve, and not a flow regulator?

Edited by TonyRPH on Tuesday 10th May 22:41

[ae173]

i havnt checked the tap yet as the mrs wont let me bring it indoors but first on the list at 6 in the morning when i get up and ive turned the carb upside down on both carbs i have and they do actualy let a bit of air through but obviously i did blow realy hard but its quite normal for these to let the air through at that sort of preasure and at low preasure no air passes

[TonyRPH]

Is the tank breather blocked, causing the fuel tank to pressurise?

[ae173]

i build scooters, quads and whatever i can dream up but this one is a quad 110 moto rama i might of thought if the tap is realy worn as i now suspect it dosnt matter if its on reserve or run it still floods.

[catman]

Surely, if the tank breather was blocked, it would create a vacuum.

This would prevent fuel flow, not increase it.

Tim

[ae173]

the fuel wouldnt come out if the brether pipe was blocked would it or would it lol just another thing to check in the morning

[TonyRPH]

catman said:

Surely, if the tank breather was blocked, it would create a vacuum.

This would prevent fuel flow, not increase it.

Tim

Well it depends if the fuel tank is exposed to sunlight - in which case pressure would build.

Surely you've opened the fuel cap on your car on a warm day, and heard that distinctive 'pssh' as the pressure is released...

Remember, when heated (even mildly) fuel releases vapour which causes pressure build up....

Of course I don't know where the OP is working on his bike / quad / whatever, but if it had been standing in the sun for some time before trying it...

Obviously once the pressure is released and fuel is drawn from the tank, a vacuum will ultimately form eventually restricting the flow..

[Major Fallout]

Tunku said:

Worn float needle?

That's what my money would be on, worn float needle and or seat.

Worn and sticking.

[ae173]

THANKS FOR ALL YOUR HELP GUYS

[cahami]

Adjust the float level, the tap is just a tap the needle valve should be capable of closing the fuel supply at a given level of float travel. check the needle valve seats properly try spinning it in its seat it may need to bed in