Adam,

Why would you bother with the problems introduced by rear mounted needle valves?

Any high quality, non-corporate-lawyer managed engine company, like Webra, YS, MVVS, Rossi and others, have the main needle mounted on the carburettor, where it belongs.

Even those 'politically correct' companies, that have the main needle mounted at the rear, still require you to get close to the spinning propeller, to adjust the idle needle, or worse yet, the idle air-bleed screw.

So what is the use of this rear needle?
Just exercise the utmost caution when adjusting the needles, or buy an engine with a rear mounted carburettor... F1 QM...58cc gas...

If you cannot keep your fingers away from the spinning prop, I would suggest knitting as an alternative hobby.