Hello,
I picked up a YS-140 sport engine a couple weeks ago for my Somenzini Yak-73" and have had some problems with transitioning from low/mid to high speed. I've broken in the engine as specified, use Power Master 20/20 fuel with an 18x6 prop, and have very good low speed idle (using an onboard glow driver). When I first start the engine and rev up to full power, the transition is smooth - the difficulty occurs when I run at low speed for a minute or so (say, during taxing) and then transition up to high speed. When I transition slowly, the engine consistently sputters and dies. However, when I transition very quickly, the engine spools up great and runs well. Therafter, slow transitions are smooth, as long as I dont idle too long. At first I though I was running too rich (the sputtering and good "quick" transition seemed to indicate this); however, adjusting the low-speed idle the full range (full open to full closed) didn't seem to improve this. Has anyone had this problem before, and do you know what can be done to resolve it? Thanks.

-Rob