We recently acquired a BSA goldstar fully restored by Len Haggis. It has the giant AMAL GP competition carburetor on it. The problem I am having is as soon as the fuel taps are turned on and the float chamber fills the petrol continues to run and flows from the carburetor top. I assumed this to be a failure of the needle and seat assembly, but upon removing the carburetor top I find that it has no such mechanism. I am now scratching my head wondering how this unit is supposed to function, what keeps the fuel flow from running continuously? Anyone have any information that can help me out with this?
Hi, welcome to the GS forum ....you should find inside the FLOAT chamber, on top of the float itself a VITON tipped float needle which effectively shuts off the flow of petrol, the original float needles did not have the VITON tip and leaked like a sieve .... . It has been several years since I last had a GP Carb in hand so if I am in error one of the guru's will guide us. I can't imagine that Peter ( Len Haggis ) would have omitted the needle .... but who knows ??
On my last Goldie I had the big GP carb., the float chamber leaked like a sieve, I bought a VITON tipped needle direct from AMAL and that cured the leaking immediately, the original needle was machined aluminium .... metal to metal contact ... did not work or me ...or many other I suspect. Prior to fitting the VITON tipped needle I lapped the seat with a mixture of toothpaste and silver polish to get a good seal .... worked fine.
By memory, if the float chamber has had a Phil Pearson conversion, then this is meant to eliminate this problem. I had this problem and sent my float chamber to Phil, he calls it a webber conversion, but can't remember if the flat bowl was retained.