Constant

A constant air leak is where there is an additional non varying opening in the  carburettor allowing extra air into the mixture. An example would be a missing  carburettor fixing bolt.

1. A reliable idle cannot be set because the idle RPM is set by the carburettor barrel (rotor) opening. With extra air going into the mixture, e.g. through a missing carburettor fixing bolt, the best idle achievable will normally be faster than required, increasing landing speeds. Effectively the tiny gap needed for the barrel idle setting is bigger than it should be, thus commanding a higher RPM than the model pilot expects.

2. With an air leak present, maximum RPM can still be achieved. The air needed for full throttle RPM is normally given when the carburettor barrel (rotor) is fully open. With an air leak present however, full throttle air is reached when the carburettor barrel (rotor) is not fully open; the difference in needed air being made up by the air leak. This difference in barrel position makes it quite easy to end up with a slightly rich full throttle mixture. The result of this can be unburnt fuel pooling in the crankcase. If fuels pools in this way in the crankcase, then after an idle run in flight, on returning to a full thottle setting, the engine can easily be flooded, as the pooled crankcase fuel is also sucked into the cylinder head, leading to a deadstick. This will often occur when a decision is taken to go round again, only to find the engine sputters and dies as the engine is throttled up from idle to max., i.e. a very bad position to encounter a deadstick.

Variable

A variable air leak is where the extra air admitted into the mixture is changing. Examples would be a loose  carburettor fixing bolt or a worn 'O' ring.

The two conditions indicated for a constant air leak still apply but the tuning now becomes variable depending on the conditions at the instant of tuning the engine, thereby forcing the model pilot to constantly retune the engine.

The solution is always the same. Cure all air leaks.

LSNV setting is way too rich

If the LSNV setting is way too rich, the engine will sputter and die as soon as the the idle RPM is commanded by the throttle stick, leading to a deadstick.

LSNV setting is too rich

If the LSNV setting is too rich, but not rich enough to stop the engine as soon as low throttle setting is commanded, then unburnt fuel will accumulate in the crankcase.

If fuels pools in this way during an idle run in flight, then, on returning to a full thottle setting, the engine can easily be flooded, as the pooled crankcase fuel is also sucked into the cylinder head, leading to a deadstick.

This will often occur when a decision is taken to go round again, only to find the engine sputters and dies as the engine is throttled up from idle to max., i.e. a very bad position to encounter a deadstick.