I was having problems with the TH .46's (I have a couple of them) until I started bench testing them.

I found that it is best to bench test the engines before installing them on your plane.

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First, if possible tune the engine with the included muffler. The included muffler seems to be the optimal configuration for this engine.

The manual tells you to start with the high speed. However you should really start with the low speed.

As suggested here, open the carb about 2-3 mm. Hold or fix it in this position temporarily.

Now close the low speed needle until hit hits the stops. Do this carefully and do not apply a lot of force so as not to damage the needle itself.

Once done back off about 1 1/2 turns.

Using a piece of tubing, blow through the fuel inlet port.

You should be able to produce enough pressure at the needle to hear a hiss of air. If you merely get a slow lessening of pressure, back off the needle until you get some flow... preferably enough to cause a hiss.

Now release the carb throttle and try the same thing with the throttle 1/2 open. The air should release far more quickly if you've done it right.

Turn the high speed needle fully in, and as per the directions turn it out about 3 turns.

Prime the engine and get it running.

Now work on the low speed needle to stabilize the idle at about 2500 RPM w/o any cutting out (though I can now get far less while still running very reliably). Adjust the LS needle in 1/2 turn increments... get it a little lean, then back off 1/2 turn or more.

Perform the pinch test.


Once done work on the high speed.

Maximize RPM's and back off 1/4 turn.

Pinch test again.


Bring the engine to a very fast idle.

Tilt the engine and tank down about 30 degrees.

Does the speed of the engine go down because it is getting rich?

If so lean the low speed out out until you get almost no change when you nose the engine/tank down.

Now tilt the engine and tank up about 30 degrees.

Does the engine stall out?

If it stalls out quickly richen the high and low a bit.

Get it to the point that it will go lean, but not stall out.

Level it off and check RPM's.

Again try to maximize RPM's at level, but richen the engine enough to where it will not stall out when pointed up.

This will be about optimal with the TH .46

Double check with your pinch tests again.

My .46's will idle very slowly, 4 stroking all the time, after all of this, and has no rough spots throughout it's entire range.

It produces very good output for it's size, and appears more powerful than my similiar O.S. AX engines.