RE: MVVS .49 Glow Plug Recommendation
Dai,
This is the oldest carburettor...
This engine must have been produced about 20 years ago, when 3D flying was non-existent.
It has a blunt-ended low-speed needle, which has an adjustable effect at idle, but is very non-linear from just above that.
If adjusted for a perfect idle, in the 10%-70% throttle range the engine will be running very rich, loading-up heavily; to the point of stumbling and cutting-out, if you suddenly open the throttle, following a short period around ¼-½ throttle.
If you only fly at full-throttle and close it to idle just to land (or can limit your flying to this regime), you can get along with it and your idle-to-full transition will be great!
But you cannot be anywhere in between - no part-throttle flying...
This carburettor is virtually a two-position switch; idle, or full power.
Unfortunately, there is no upgrade kit available for this carburettor...
For the 'in-between' carburettor design, that had virtually the same body, with a rigid high-speed needle, with an external thread, there was such a kit (#3216-0253), but it will not fit onto the carburettor that you have.
On the positive side, this carburettor has its O-ring located at the bottom of the insert - below the draw-bolt, where it potentially precludes all leaks from affecting the engine...
If you intend to run your engine reliably, at varying throttle settings, you will need to replace that carburettor with the new one #3216 (see photo), which is probably the most linear glow carburettor you can get (several members here can attest to that).
Thankfully it is not very expensive.
This engine seems very clean and in good condition, so the investment is probably worth it.