I'd appreciate some further input into this issue.
I got a new gasket the other day to replace the faulty one - Amal 622/073 Float Bowl Gasket - MK I Amal Concentric Carbs. This is a genuine Amal part, but is different to the old gasket and the one on the other carb - which I assume to also have been a genuine Amal part as it was attached to the new Amal 930 carbs that were installed when the motor was rebuilt a few years ago; the float bowl has never been removed until now. On one of the vendor sites that I looked at there were several different part numbers for gaskets, with a statement "use 622/073"; so I wonder if there were different forms of gaskets produced by Amal in the past, now all replaced with 622/073.
I don't have a photo of the new gasket but below are pictures of the two carbs; one with the original gasket which is visible and red; the other with the new gasket installed which is narrower and thinner and invisible.
The issue that I now have is that with the new gasket in place the float bowl is leaking petrol past the gasket onto the outside of the float bowl. This has happened when the bike is on the side stand, so that the level of petrol may have gone above the gasket, but I didn't feel like starting the bike with petrol dripping so close to the cylinder block. If it leaks on the side stand presumably it will leak when the bike is leaned; even if it does not when the bike is upright.
It seems to me that the issue is that the new gasket is thinner than the one that it has replaced. It is possible that the float bowl has formed itself to the prior thicker gasket, and that there is a slight curvature in the bowl; the photo suggests that at the point where the screws attach the bowl the gap between the bowl and the carb is less than around the body of the bowl.
I have emailed Amal to ask about this; and have received a pretty prompt reply asking for more information, and expressing surprise, so this enquiry to members is running in tandem with my communication with Amal.
When I took the float bowl off the float came out, so I have had to reinsert it. It is possible that I have mucked up the level of the float, but I don't think so, I just put back the little pin and hooked the float to it, and made sure that the rod running through the float was in proper position.
So the question is how to stop the leak. I am assuming that there is no replacement Amal gasket that is thicker like the last one was.
Subject to what Amal suggests I suspect that I have the following alternatives:
1. See if I can bend down or file off the part of the float bowl where the screws attach the bowl to the carb - the gap between the bowl and carb at these points is less than around the rest of the bowl; but that might just be a function of the bowl bowing when the screws are tight;
2. carefully rub down the float bowl on sandpaper over glass to try and get the bowl absolutely level - a variation on 1.
3. try using two gaskets together instead of one. That would be my preference, as it would be the easiest solution. But would it work? Would there be a potential leak between the two gaskets? Is the thickness of the gasket of essential importance for the operation of the carburettor i.e. would the level of the float be compromised?
4. Get a non original thicker gasket. Is there such a thing?
Thoughts appreciated.
Isn't it typical with these old bikes that a minor issue - in this case touching a $2 part, can cause hours of communication and frustration sourcing a part and weeks of the bike being off the road (as it happens I ordered the gasket from one NZ supplier with some other things; the order was processed and the gasket omitted - out of stock despite the website stating it was available - and the other non essential stuff arrived - I had to reorder from another supplier - so a week or more lost right there).
