Yeah, those white plastic caps on top of the carb covers that disintegrate after a while. Is there a replacement for it that someone makes?

What I did with mine was to silicone a 1/8" thick nylon washer and a beer bottle cap on top of it but after about 6 months the silicone gave up. I used Ultra Black RTV silicone and the air leaks were so small that using a propane during idle did nothing. When I switched to ether (starting fluid in a can) is when I noticed the leaks. The bike idled fine and it ran perfect but it did pop during deceleration. Chasing this problem I did replace everything else, exhaust gaskets, spark plug caps - wires, and air cut-off valve rubbers. This time I cleaned it all up and I glued it back on with Ultra Copper RTV silicone and I'm just hoping it will last. I have epoxy resin and I didn't want to use it because on many occasions I saw it peeling off the plastic parts.

Epoxy seems to be the way to go:
http://www.randakks.com/TechTip55.htm
Some have used a nickel instead of the bottle cap. Looks kind of cool...

could you jb weld the cap in place

could you jb weld the cap in place

I just got some JB Weld yesterday and I'll try it. As I said in the previous post, I hate to use epoxy because I have seen it peel right off after some time.

JB Weld did work wonderfully. I was surprised of how well it flowed compared to the 3-4 year old tubes I had laying around. The Ultra Copper RTV silicone did not perform well on the nylon washers and the plastic that was on the covers and it peeled right off. I have to keep reminding myself that silicones are only good with a combination of mechanical fasteners.