Pit-Viper 1

My Feedback: (12)

I have a brand new .75AX and an older .91FX and both of these motors knock loudly when running. I am wondering if this is normal or is this a pre-ign. knock? I am at 3500' above sea level. I've read that shimming the head helps this. I've tried different plugs (warmer, colder) but no change. I use Powermaster fuel 20/20. Here's a video of what I'm talking about.

[link]http://www.youtube.com/watch?v=rr85ZFguNG8[/link]

Thanks Shane

Bax

My Feedback: (11)

What you're hearing is not "knocking". At the part-throttle setting you're using in the video, the engine is misfiring a bit. That's of absolutely no concern. ANY model engine will tend to do that. You're hearing an exhaust note and no actual metal-to-metal contact, nor are you hearing true ignition knock, which is caused by a too-lean setting at high power levels.

Get the engine running well at full throttle, get the low-end properly-set, and you'll be OK.

Pit-Viper 1

My Feedback: (12)

Ok thanks Bax.