G'day Mate,
Sounds like it is too rich, here's what I do, first you need to find your tuning range.
I always use an extension on my needle valves, just a piece of wire, with a circle bent on one end & a flat filed on the other,
put into the needle valve, & tighten the grub screw, it's usually a 2 mm grub screw, & the Allen key comes with the engine.
Start the engine, & at full throttle, very slowly wind the main needle in, until the revs start to drop, this is your leanest point, note the position of the wire circle, on the needle valve extension.
From there wind the needle back out & note when the revs start to drop, this is the rich point of your tuning range. Now you know the tuning range of the engine,
just wind the main needle in, about 3 to 5 clicks, hold the plane vertically, & the engine should speed up slightly, meaning it is rich enough, it is now ready to fly.
The tuning range will vary depending on fuel, ie amount of nitro, more nitro, wider tuning range, prop, temperature, altitude, & other variables.
But whatever you do, don't be tempted to lean it any more than those few clicks.

Cheers.