Hello Peter,

I just got my bike ready and running. So this is a work in progress. I had exactly the same problem. It took loads and loads of messing about to get the float height right and the needle valve to seal when the float bowl is full. I was told that it is very important to get the top little button of the needle moving really freely in the little fork on the float leaver. I took it out and polished it and tweaked it so many times. An long experienced Indian guy told me this is the only way!

I have the mixture about right now. So float height is okay. The sealing on the needle is okay while the bike is running, but if I leave the fuel on with the bike stopped the fuel slowly fills the bowl and overflows. So when I start the bike I turn the fuel on and let the bowl fill then turn the fuel off. Once the engine starts I turn the fuel on again, Also I make sure I turn off the fuel as soon as I stop the bike and it's okay. 

Cheers, Jon

Sad to hear that you have had several issues with your restoration!

A refurbished carb to factory specifications should not dribble!

Was the old needle cone ground and polished to mirror finish? It should be ground to somewhere 30-45 deg, but the angle is not overly important, if the needle is used to form the seat. In that case you should perhaps save and use it because in some cases the orig needle is lighter than a reproduction. 

Is the needle seat thin? I like mine to be about 0,4mm/.015in when refurbished, in order to seat easy and be less sensitive to side loads that can knock it out of alignment. And I always burnish the seat only with hand pressure, never tapping. Never ever in any case I got a seat tight with any grinding compound. Even tried toothpaste but that is useless, doing absolutely nothing. 

The needle arm needs a fine fitting on it's pin. A sloppy twist- and side-to-side fit and the needle is easily knocked out of alignment to the seat.

Most people think that a wider seat will be tighter, but in fact it is the opposite if the force that the float is exerting upon the needle is the same. The force per square mm or In. is higher the thinner the seat is. A larger surface area does not seal better, on the contrary, the force per area unit lessens and makes it easier for the fluid to pass. Because of the fluid viscosity of the petrol, and imperfections in the valve, alignment and wear resistance, the seat however might need to be broader than just knife edge thin.

Most importantly, one needs to visualise the float working in situ, before it is affixed to the carb body !  Floats float, so with the carb bowl detached, observe it floating whilst adding fuel directly to the bowl.  It may act like a 'sinker' and stay on the bottom, or it may have partial bouyancy.  You may also sight any restrictive contact, that the float may have, with the bowl side.  Observe the bowl for sometime, for leaks, in and around the needle seat area.  Float height, as mentioned is important.  It measures 7/16" from the bowl's top rim, to float, once fully floated by fuel.  Hope this helps.  A bung or finger may be used to plug the bowl hole before filling.

Mine suffered from exactly this issue.  The root cause turned out to be the needle seat was loose in the carb. casting, allowing fuel past the needle/seat joint, even when the needle was a perfect match to the seat.

I carefully tapped the seat back into the casting, and have seen no more leaks to date.