Dear Bax,

Sorry, this may qualify as a double post since I just found this forum. I have been trying with only modest success to tune the idle on my 46 FX - it has been run in according to instructions, and is set slightly rich ( - 300rpm for a final on the ground of 11,000rpm) on high speed, with reliable idle around 2800, #8 plug. It's a "new" engine - just in storage for a number of years. Prop is APC 11 x 6, Fuel 5% nitro, 20% oil (synthetic/castor), mounted in a Great Planes PT 40. I followed the instructions for screw re-set (I think I may have gone past the sweet spot by using increments that were too large). The instruction for the 46 FX (not AX) say to wind the screw out around 1.5 turns after having closed the carburetor barrel and wind the screw down to the stop position (clockwise). My question is that there reaches a point where winding the mixture screw down itself seems to open the carburetor barrel, is this normal? If so, I assume that the true "stop point" for the idle mixture screw is the point at which it begins to force open the carburetor barrel and I need to wind out around 1.5 turns from this point. Under normal circumstances (ie, 1.5 x turns out) would you normally expect that to be set slightly on the rich or lean side for smooth idle and transition? At my best setting so far before starting over (and so, my question above!), I got good transition but some hesitancy at the medium- high end, and at idle the "pinch test" needs at least 10-15 seconds to note any increase in speed (too rich?)

Any help, much appreciated.

best

Beej

When the carb is closed, you'll feel it gently touch. Then open it.

We usually set it so that there's about 3-4 mm of gap when the engine's wide open.