250 Mono Carb Fault

[scrappington]

Picture this cleaned carb, (spotless) fitted carb, turned petrol on, petrol leaking from botton overflow not the top 2. Tried blowing down the fuel pipe and the cut off valve is working ok.

Please help im sick of taking it to bits and finding nothing wrong.

[john collins]

Very often the float needle and seat on the mono.

Asume you have checked float height - measure float height with carb upside down - if you have no manual I can look that up for you.

Although it then often seems that the valve is shutting off the flow - it does not always do so.

Sometimes this becomes more obvious if you attach a piece of tube to petrol intake pipe and see if you can very gently blow through when the carb is still in upside down position - if you can ie the weight of upside down float is not shuting off the flow of your blow !!! - then I would suspect you need new needle.

If you change both the valve and the brass seating insert - which screws out it usually does the trick

[feetupfun]

The top "overflows" are vents. Fuel will only come out them at extreme angles ie if the bike is lying down or upside down.

If the float needle valve really is sealing properly, you may have a split in the overflow tube (the 3mm diameter brass tube that sticks up through the bottom of the float bowl and has a nipple under the float bowl) The split may be very hard to see.

Depending how you are doing the blow test for the float needle, you may not have eliminated the possibility of the float level being set too low.

If the overflow tube is not split, check the float needle a different way ie by connecting the carby up to a fuel source with the float bowl off and very gently lift the float arms to replicate what the floats do then turn the fuel on.