Royal Enfield Owners Club,  Humberside Area
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Amal Monobloc Carburettors have no facility to alter the float height and hence the level of fuel in the float chamber.
The fuel height is just as important as in other carburettors however, so it's a bit of a mystery why Amal didn't design in a method of adjustment.

I recently took over a Triumph Cub (not bought yet, just living at my place for a bit) and the carb showed every sign of being on the brink of flooding all the time. Especially annoying was the spluttering when opening the throttle after having it closed on the over-run.

I took the float chamber cover off and found that the float had to be all the way up in the float chamber before the float needle closed  which suggested that the float height was too high.

After Googling round on the net for a bit I found out that early monobloc carbs did not have the washer under the needle jet housing. This is supplied with modern repair kits and often fitted in error.

Sure enough, the Cub had this washer fitted so I removed it. It's not required anyway as the flange is quite wide and seals quite happily without it.

This helped with the flooding somewhat but  having got this far I thought I'd try to find out what the float height should be.

More Googling disclosed that the "pip" on the float chamber cover indicates the correct fuel level.

But how to find out what the actual fuel level is on my carb?

The trick is to remove the cover from the pilot jet (this will drain the float bowl) 

Push a suitable length of plastic pipe on to the pilot jet, and lead it round and up the face of the cover.

When you turn the tap on to fill the float bowl again the level in the pipe shows the fuel height in the bowl.

I found mine was still high even without the washer - came to about here.

So I went and had a cup of tea to puzzle this out for a bit.

I came to the conclusion that the carb. must have had some "odd" bits used at some time for the fuel height to be this far wrong. The only parts which could effect this are the float, float needle and float needle seat. (I'd already checked obvious things like bad needle or leaking float)

I had  no spares to compare so had no idea which was the culprit and I didn't want to buy more spares then I needed (the needle seat especialy is quite expensive) so back to good old Google.

It seems the fix is to machine a bit off the bottom of the needle housing.

It's made of plated brass fortunately, so I was able to do it in my wood turning lathe (I don't have a metal lathe)

I just had to be careful to keep the face flat and square (somewhat time consuming working by hand)

I took off roughly 0.010" which brought the level down somewhat but not quite right.

Another 0.010" and it was spot on!!!

The bike now starts better, runs and ticks over better, and the annoying "cough" as I open the throttle has gone.

It now needs tickling from cold before it will start, which is, of course, how it should be.


I've since been given the following information about adjusting the fuel height.

On the old copper floats you can add a blob of solder at the point where the needle bears.
You could file this down to the correct thickness.

On the newer plastic floats you can wrap a bit of suitable sheet metal round and tuck it under.
Again, where the float needle bears.