I can´t get the best RPM with a Propeller 12.25 x 3.75. I am using a Mini Pipe.
First of all I discovered, that the spring of the low needle did not adjust very well, so, I replaced for a new one.
Now I have two questions:

1.- How many turns need the low needle, because the manual said 1.2 mm
2.- How separate should be the Pipe from the tube ? Some said 1/2 inches. some said 2mm

Luizinho,


You did not write what .49 you had.

If it is a new engine, or more importantly with the new #3219 carburettor, the initial position of the low-speed needle is 2 mm out from the throttle arm nut.

If you have the old carburettor, the 1.2 mm setting is correct.

You can tell what carburettor you have by its appearance.

The new carburettor does not have an idle-stop screw on top (it has a grub-screw with lock nut on the back, for barrel location), the air-horn is elaborately dished and the low-speed needle has a flat screwdriver slot.

The old carburettor has a crossed screwdriver slot, a simple air-horn and an idle-stop screw.

See photo of a new engine with the new carburettor.

MVVS strangely still includes the old carburettor instructions with new carburettors and engines...


About the header-coupler, it does depend on the version of the header that you have; there have been longer and shorter versions (3 different lengths), but for this heavy-load prop, you will want a longer combo, about 5.5-6.5" (140 - 165 mm) between the engine's exhaust stack and the front nipple of the black mini-pipe, for best performance, depending on fuel, among other things.

Too short a pipe can cause a lean run (damage to the engine), so longer is better.


About the low speed needle, some Teflon sealing tape can augment the spring and the needle will not move under vibrations.

Hi, DarZeelon, thank you for responding. Here are som pictures, so you may identify.

Luizinho,


From the molted color of the cylinder head, your engine appears to have been run a bit too hot, although this is no cause for immediate concern.

It is definitely the new engine, with the new carburettor. This means the starting setting is 2 mm from the nut.
Adjustments are done in single clicks; not in 1/4, or 1/8 turns. The adjustments for this needle are very fine and 1 'click' out from the ideal setting, could mean a dead-stick landing, or worse, for a low flying 3-D model.

The header that you have appears to be the medium length variety.
You should extend the distance between the header and the silencer to 15-25 mm, for the 12.25x3.75 prop.
And also turn the silencer around itself, to minimize the bend in the silicone coupler.

Dar Zeelon, Thank you. I will follow your advice. I'll let you know.

You should have a look at your carb, the spray bar is pointing in the wrong direction.
The fuel inlet nipple should point more or less parallel with the cooling ribs....not up wards.

Really ?? I will see that !!! Thank You, MicroMac. I could never notice that. Thank You Again !!!