[brucepick]

Also interested to know more.

Mugen, as you're working on this, can you say. What air:fuel ratio the stock HX has? I've always wondered. And of course tell us what AFR ratio(s) you build into your box.

Marvel Mystery Oil has been mentioned here and yes, I use it in every tank. It gets me lean burn down to about 1800-1900 rpm. Could take you a few tanks with MMO to get those results but its worth it.

I tested various ratios for MMO and settled on 2 oz. per 10 gallons fuel. I got a ADJUSTABLE one ounce measuring cup from a cooking store to measure it out, and a funnel with tube. Cup is available from Amazon for just a few bucks, also.