Fuel in crankcase

[Rusty]

Isn't it an E model? No diaphragm.

[Daisy]

Correct. Its an E model. The D model has a vac tap and no reserve switch - just the warning light. Can't be swapped over either, because the E model has a deeper tank that is lower than the carby bowls and fuel has to be pumped.

[Daisy]

Ok, I finally braved the cold and removed the carbs from the bike. I set them in a jig to mimic the location in the bike and connected the fuel tank about 20cm above them. I turned on the fuel tap and there were no leaks - but, after I blew air into the breather pipe they all leaked.
The top one stopped after a couple of minutes, but one was still leaking after an hour. Looks like I'm in the cold again tomorrow to strip them down again.