BTW: The A3 is NOT a good plug for the Tower Hobbies .46 engines and above.

The T.H. engines come with and need a "long" plug, such as those used for four strokers.

Also be sure to use a heavier prop, such as an APC. Many engines work and idle much better with the heavier props. This is one of the reasons for the "inconsistencies" between people purchasing these engines.

Keep a long plug on it, with the proper APC prop, and it's an easier to tune, more reliable engine. After it has been run for a while ( 2-3 gallons ) you can usually switch to the lighter props.