BSA Owners' Club Workshop Discussions

I am nearing completion of restoring a 1946 BSA B31. The bike starts and runs OK but it runs very rich such that after a few minutes to warm up and a few hundred yards up the track the plug is covered in black soot. The air screw is well open and the needle is at position 1, the lowest. I have installed a new main jet as it was easily available on eBay.

I would be grateful for any suggestions as to what else I might try.

Thanks

The AMAL web site gives a 150 main jet and assume this is roughly what your carb has? I would definitely start by checking the float level and checking that the cut-off valve is working correctly and the float bowl is not flooding.

Thanks. I will investigate the float chamber although petrol is not flooding out. I can confirm that the main jet is 150.

I am not particularly familiar with the AMAL 276 carb but looking at the parts diagram it looks as though there were two versions: one with the fuel valve at the bottom of the float chamber and the other one with the valve in the top cover. For the former version, it appears to come with two needle positions and, if you have this version, it might be worth checking which needle position you have.

I don't know how to set the float level on a 276 but I saw a video of someone doing this by fitting a manometer tube after removing the screw in the feed flange underneath the carb and then checking the fuel in the tube was level with the air screw. Not sure whether AMAL provided a pip on the float chamber for this purpose as they did on the float cover on the Monobloc?

Thanks again, I will check to see if there are 2 positions for the float needle. The fuel valve is at the bottom.

I thought it might be useful to post the resolution of my problem with the carb running very rich. The problem was with the float where the clip on top was waggling about and causing the float ball to slide up the needle valve. I found out from Burlen that a replacement float and needle was available in plastic so I bought one and my problem is solved. Thanks to all for your help which is much appreciated.