Fuel leak fixed

[GrahamFountain]

Had a smell fuel leak from the overflow pipe on the front carb - more than a drip, but less than a drizzle – but only on tickover. I had noticed that the tickover would fall a bit while stood, presumably as the chamber overfilled and mix went rich on the front, but the fuel consumption wasn't obviously up, and I could only smell petrol when stopped.

At first I thought it must be the float chamber needle valve. But I had replaced those after the engine swap last summer with black Viton rubber tipped ones – after being stood for a while, the red tipped ones in there were sticking to the seats and starving the carbs of fuel –, and was rather expecting the new ones to last more than 6 months.

Anyway, I had a couple of goes at taking the needle out and giving it a good clean, inspecting it for damage or embedded crap. There was a discernible ring indented into the rubber, obviously where it sits on the seat; however, no damage or grit obvious with a pair of Poundland's best 300 reading glasses.

So I ordered a replacement, and muttered. When it arrived, I went to pull the valve seat only to find that it wasn't fully screwed into the lid. Not so loose that I'd felt it when I'd pulled the needle, but obvious when I put a socket on the seat. So I just tightened it up and put it all back together, and the leak's gone.

I know I'm a bit leery of over tightening the brass seat into the s##t metal (zinc-aluminium alloy) cap, but I thought I had it tight enough it wouldn't shake loose. But obviously I'd just wasn't tight enough, and it had managed to unscrew itself and leak down the threads.
I'll see if the wandering tickover problem's cured today when I go to market to buy a fat pig. The jiggerty jig on the return home should see if I've nipped the seat up enough this time.

Graham

[trackerjack]

There I s a great feeling of satisfaction from finding a fault and knowing you have fixed it.
I have had many problems with SU parts over the years as they are so crude when compared with motorbike carbs fitted to Jap vehicles that use the same principle as SU's. However they (Jap) are much superior in manufacturing technique than the old fashioned Brit stuff.

[tony g]

Nice find Graham, one for the memory banks

Tony