Another Monoblock carb problem...

[BOBLAN]

I have a 1946 B31 and bought a brand new 276 Amal from Burlens a year or two ago. I haven't used the bike much since then, but I am having real trouble with the float chamber continually flooding. As soon as I open the tank tap, fuel spurts out of the two holes in the screw cap of the float chamber and out of the carb itself.

Having stripped the float chamber many times, it seems that the fuel enters from the bottom until the float rises and seals the "valve". The "valve£ just seems to consist of the cone shaped end of the bottom of the float spindle being pushed (by the pressure of the fuel), against the brass seating. With the problem as described above, it seems to point to the valve not sealing properly, even though it is a new carb.

Is my thinking correct, or is the "valve" missing something? Any ideas how to cure it?

Thanks for any suggestions!

[Spaceman]

It should be possible with the float chamber cover off to see what is going on and to check if you raise the float or needle whether or not it cuts off the fuel.

I vaguely remember there were 2 x types of float fitted to the 276 carb but I understand this one has the valve in the bottom of the float bowl. I believe there are 2 x positions for the float needle and, if so, it might be worth raising the needle to the upper notch is not already set at this. If the valve appears to be sealing, it might be worth checking that the top of the needle is not fouling on the cover.

[BOBLAN]

Yes, thanks, I have tried the float. The float spindle does have 2 grooves in it, marked C (top one) and P (bottom one). The Amal instructions state that the newer plastic floats need to be in the lower P groove. I have tried both, but it doesn't make any difference to the flooding.

Thought I had sorted it today, just by stripping it again, cleaning and reassembling. Nothing flooded when I turned the petrol tap on, even after 10 minutes. So I started the engine and all ran OK with no leaks. Stopped the engine, turmed the tap off and left it for a while. Then turned the tap on again, and it flooded out of both the top of the float chamber and the mixing chamber!

There is no dirt in the vlave or the float chamber, and the float does not leak. I have also tested it in water, and can see the water come up to the correct level at the top of the float.

So I have no idea. Perhaps I need to talk to Burlen? 

[Dean Southall]

I have had this problem with the 278 floar chamber flooding. Filing a little off the bottom of the tickler fixed it!

[BOBLAN]

Thanks

I did wonder about the tickler. But I checked it with the float on the upper groove setting and there was about 1/8" play before the tickler touched the top of the piston. But with the float in its correct lower groove setting, there is more like 1/2" clearance, so I think that might be ok.

However, your suggestion then prompted to think about the length of the float spindle. If that is fractionally too long, it might prevent the float coming right back up. I'll check that out tomorrow.....

[Dean Southall]

Check there is not a blockage or friction in the hole in the float chamber top. More likely than an overlong needle.

[Steve.S]

From what you have said, I'm sure we are talking about a pre-monobloc carburettor, even tough you have entitled it Monobloc.
It's interesting that you have had a situation where it doesn't flood, indicating that there is not some manufacturing fault.
As Spaceman suggests, you should see what happens with the float chamber top removed. Is the needle bent at all?
It maybe worth using a little Brasso on the seating, just to polish it, in case there any high spots. You should then be able to see where it's seating or not.
I wonder if the needle is sticking in the float chamber top. Maybe apply a little light oil, although it won't stay there long.
I assume that if you pull the needle upwards with the top removed, it stops flooding?
It doesn't take much to prevent the needle from seating, so it may be worth filling an in line filter.
Let us know what you find.