Hi all still having fun with my carb try lots of things now found its a little hole under the throttle screw where the petrol leaking from!!!
Any one know what's causing the petrol to come out of there is it the jet block? Any help would be great regards Keith.
The reason is usually the fuel level at the float chamber.
Few things can be the reason:
The float chamber valve could be leaking and may need some lapping
With a fine carborundum, or if this needle valve has 2 notches,
Mybe the top notch/grove is at use and not the bottom one,
Sometimes, in the brass floats, the lock for the needle
Was soldered few times and deformed,
(But that usually would lower the fuel level, not raise it)
And because the fuel level is relative between the carb body and the float chamber,
Sometimes it can be just the usage of gaskets of the correct thickness at the correct places.
Thanks Noam check them seems to be okay but you can never tell can anybody tell me what the small hole is for? once again thank you for your help Keith ps. Don't you just love things you can't see in Front of your nose it would be something simple and easy to do but just can't see it struggling but will persevere ha ha!!!
The small hole on the 276/R (the 'R' is important as it indicates this aspect amongst others) is an overflow. In the absence of this overflow, excess fuel would either enter the engine or flow back out of the inlet.
Fuel cannot reach this overflow from underneath which means that it is flowing from the needle jet and out of the jet block.
There are only two possible causes for this. One is that the float level is too high. This can be checked by removing the float chamber cover (the engine will run statically quite happily like this). Fuel level should be half way up the level of the pilot air screw. You can jury-rig a clear plastic pipe for a better view.
It seems possible that the specific gravity of modern fuels may be a little low for some of the heavier original brass floats. I now run my Norton with a 'long' mixing chamber nut originally from an OHV in order to lower the float level. The brass float is noticeably 'slow' to shut off and will sink at the slightest touch.
The other cause is simply that the float needle is not shutting off properly. Seats and needles do wear.
I've tried lapping but never really been successful. The best option seems to be to tap the needle onto the seat with a parallel punch...but not too hard.
I suspect that if I wasn't keen to experiment, a new chamber from Burlen with new-type float and needle would probably be the thing to do.
There may not be anything wrong with it. Petrol will seep out of that hole (and also the hole in the float chamber lid) when you tickle the float chamber for starting, as the level is raised. You only have a problem if it comes out when motoring normally. Its not like a modern bike, there will always be a small trace of petrol around the carb, just live with it.
