Curlew carby issue .... I think ...

[Arbian]

Motor was sent to me with head nuts loose as tank was removed for transit so I had head off and had a look. All looked fine with head and bore so I got new gasket and refitted with sealant and torqued to 18 ftlbs. Are there any issues I might have missed that could be causing this?

[Collector Inspector]

This sounds like a classic air leak to me.

Crankcase or similar perhaps.

Yes strip it down.

BnC

[Oyster 49]

Have you tried fitting an alternative carb? This could help isolate the problem? Is the carb slide worn?

[Arbian]

I don't have another 418, could I try it with a 416 off a non QB? Is the carb slide the piston that the needle sits in? There was a tiny bit of corrosion on the side of it ... still seemed to slide smooth enough but that was by hand without the force of a trapped spring behind it ... everything else seems corrosion free.

[Oyster 49]

Yes if the slide is worn, then it is the classic cause of an uneven tickover in a classic bike with an Amal carb..
It could even be a sticking slide that will not slide fully down, due to a distorted bore.

[Arbian]

Well, after being on hols I thought I would have another crack at the Curlew. Sparked her up and all as before. Removed the carb piston assembly and noticed the plating on the bottom of the needle was worn. I didn't imagine this could have much impact but swapped it with another off a spare 416 carb (both seemed to have an 'R' stamped at top). Anyway after so doing things seemed greatly improved and I re ran Charles carb set up routine. Lo and behold it now seems to be running ok. Can't get it to near Hugz tickover but it seems quite acceptable.