Carburetor hole in one.

[GrahamH]

Whilst fitting the carburetor to my 66' 305 Dream I noticed a hole, probably a drain hole, which sits under the carb' and leads through to inside the right hand casing. I didn't measure the hole but it is certainly big enough to swallow a dropped M6 nut. Don't ask how I know this, just be careful and put a piece of rag to cover it whilst fitting the carburetor. It's probably the same on the more sporty twin carb bikes too.

.............GrahamH

[Tim Allman]

This sounds like the path for the breather tube. The nipple is on the top of the engine. The tube should be attached there, go under the crankcase cover and through the hole that swallows hardware.