The hole truth

It‘s been a carburettor month in Rick’s world, so to kick off here’s a game-changing Amal GP discovery

In last month’s Goldie update I said that, while I’m content with the BSA’S power, I’ve fitted a Concentric carb because starting’s too unpredictable with the original

GP – maybe first kick, maybe nothing... and then it won’t even bump start. Sometimes it just says ‘boof!’ which I translate as ‘gimme more gas’ – but tickle it at your peril, Goldie’s flood easily.

Goldies start well on modern carbs, so the GP gets the blame – ‘It’s a race carb, useless on the road’ – but who wins races on bikes that don’t start? Older friends who had Goldies when they were quite new recall no trouble starting – apart from careless tickler use. In fact, my uncle could bump his Goldie inside his shed – just eight feet long!

I’ve been looking at the pilot system; it affects much more than just tickover on a GP. Where most bikes have a petrol jet and a tapered air-supply screw, the GP1 has an adjustable jet – the pilot screw is a fine-taper needle that regulates fuel flow through a small drilling in the carb body. Goldie lore warns against winding the screw in too far and damaging its taper end, but what about the hole? Mine appears tapered to match the needle and I’ve just realised it shouldn’t be – the needle’s stretched it. Wonder how many other GPS are the same? Hmmm, a taper needle needs a straight-sided hole; with a tapered hole adjustment is not linear, it’ll open up too much, too quickly – making for on/off adjustment. My screw’s always been super-sensitive.

I’ve had this carb since I was at school – it came from my uncle and I rang him to see what he remembered. He said it was a spare he’d never used, not the ‘eight foot start’ one! Phil at Burlen Fuel Systems tells me the original hole was 0.032in, mine’s at least 0.050 at the wide end. Since it’s not a replaceable part, I’m going to have to sleeve the hole hoping I get it right – it’s no good as it is. Wish me luck!

‘MY UNCLE COULD BUMP HIS GOLDIE INSIDE HIS SHED – JUST EIGHT FEET LONG! ’

Examination of the pilot hole on the GP1 has revealed it’s not the taper needle at fault – it’s the hole itself

WHO IS RICK? Rick Parkington has been riding and fixing classic bikes for decades. He lives and fettles in a fully tooled up shed in his back garden.