Model Tech Magic Formula 3D ARF Manual page 37

WARNING To prevent dust and debris from entering your engine during the fitting and aligning of the cowling, we strongly
suggest covering your engine's exhaust port, carburetor opening and needle valve inlet with small pieces of paper towel.
When satisfied with the alignment, use pieces of masking tape to hold the cowling securely in place and aligned.
STEP 2: MOUNTING THE COWLING
Remove the spinner backplate and cowling, then install the muffler assembly onto your engine.
Measure and mark the location on the cowling that you must cut out
to clear your engine's cylinder head.
Scribe lines have been molded into the cowling as a guide for most
two-stroke engines, although we suggest double-checking the location
and adjusting it to suit your particular engine.
Using a rotary tool with a cutting disc and a sanding drum, carefully
cut out the cowling for your engine's cylinder head. Work slowly,
removing small amounts of material at time, checking the fit often.
Temporarily slide the cowling over your engine and onto the fuselage,
then secure the spinner backplate onto your engine's crankshaft.
You may need to remove some material from the front edges of the
engine mounting beams, so that it doesn't interfere with the cowling.
Line up the front of the cowling, using the spinner backplate as your
guide. When aligned properly, the cowl ring should be centered with the
spinner backplate and there should be about a 1/16" wide gap between
the front of the cowling and the back of the spinner backplate. The
painted trim on the cowling should line up with the corresponding trim
on the fuselage, too.
With the cowling held firmly in alignment, drill 5/64" diameter pilot
holes through the cowling and into the fuselage for the four wood screws.
Position the holes 1/8" in front of the back edge of the cowling. Two
holes should be positioned on each side of the cowling, spaced
equally apart.
IMPORTANT Don't drill the pilot holes farther forward than 1/8" in
front of the back edge of the cowling or they will miss the sides of
the fuselage.
Mark and cut out the area of the cowling necessary to clear your
engine's muffler. Again, remove small amounts of material at a time
and test-fit often so you don't remove more material than necessary.
IMPORTANT If you haven't already done so, cut an air-exit hole
in the bottom of the cowling, behind the cutout for the cylinder head.
For proper engine cooling, the total area of the air-exit hole should be
approximately 30% larger than the area of the air-intake hole .
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