Last fall I picked up a Funtana with a YS .63 for a fair price. I was told the engine was only broke in, but when I ran it on my test stand it kept betting air bubbles in the line feeding the carb. I put a gasket set in and replaced the diaphram. it seemed to work on the test stand. I reinstalled it on the Funtana and under load it started to run lean again (air bubbles in the line feeding the carb). I'm at my wits end and asking for help.

Thanks
Dave Simmons

The bubbles in the feed line are NORMAL. Look to a cooling issue for your lean problem. Either it's over-propped for the fuel you are using, or you are running the wrong fuel for your local conditions.

Dave, I finally got some time to try your suggestions. Running Omega 15%, I got 12k rpm with a 12.75 x 3.75 prop.

Thanks Dave Simmons

Let me know how it works out.

Is The regulator screw set flush to the housing. I was having the same problem with my YS 63FZ in a funtana. My friend who has several YS engines suggested setting up the engine with the regulator screw set flush. I had the ability to run the engine 3/4 turn leaner with the reg screw set flush. Also I was having problems with air bubbles. Are you running the engine with a fuel filter? Is the filter screwed in tight?