razorback

If the .91 is like it's smaller brother, the .61, I can say that the engine should not be fussy on plugs. Recently I have used K&B 1L's in mine. They seem to work well and are readily available. MVVS also make a "cool" plug which works well, but is only seems to be available from MVVS dealers and agents.

I have also used Rossi 5's, but they are hard to find and expensive.

It seems they like a standard long reach plug that is just a little cooler than your usual OS A3's, 8's, or Enya 3's.

I found that with Nitro the engine would not peak (pre-ignition at wide open throttle), and that when started by hand (as I prefer to do) it would fire and run backwards.

These are my experiences, others may have had no problems at all with standard warm rated plugs. Try whatever plugs you have on hand (I seem to have a fair collection after many years in the hobby) and see what works best for you.

Another tip - a little loctite thread lock on the muffler hold- down screws works wonders. Apply when engine is at temperature, and let cool. That should stop any tendency for the screws to come loose in flight.

Check out the neat clear "O" ring on the carby intake spigot, and the positionable cylinder for side or rear exhaust. I found them to be nice engineering touches on a well thought out, robustly constructed, engine that sells for a very fair price.

fiery