ULS pistons and Jugs on a UL

[Norm]

In December my old 912 UL started to run poorly. When I checked the motor with a leak down test it failed. A further inspection revealed the end gap was three times the normal end gap. I talked to Hal and he let me know that he could provide the UL pistons jugs and rings with very little wear for about the price of rings from rotax. He also mentioned that that he could upgrade me to ULS pistons and Jugs for not much more. (actually about twice the price) but it didn't take me long to say yes to that upgrade. I put the pistons and jugs on during the cold snap in Feb in an unheated hanger but it was too cold to fly so I thought I might as well fix.
I saw some improvement and some great top end. In fact my rpms seemed to be about 400 to 500 rpm higher and my top end increased about 5mph. In spite of the improvements the motor was not as smooth as I wanted. It seemed like no matter what I did the carbs would not balance. In talking to Hal he noted that the ULS has smaller jets and a change might be in order. I ordered new jets and a rebuild kit after fighting with the carbs and balance for almost a month. I did my first flight today with the freshly rebuilt carbs and new jets and WoW what a difference. So far I have just synced the carbs mechanically and it is the smoothest the plane has flown in quite a while. I did not see the higher rpms that I had seen previously but I will continue to work on it and do a vacuum balance. As Hanibal from the A Team would say "I love it when a plan comes together."

[avidflyer]

If you don't have the carbmate tool, you can use a single vacuum gauge, a T in the line coming out of the vacuum gauge, 2 valves in lines coming from the T and lines going from the valves to the intake manifolds. Open one valve, read the vacuum, close it and open the other valve and read the vacuum there. Adjust till both sides show same vacuum. JImChuk

[Maverick]

Got a picture of that?

[avidflyer]

Here is a very crude sketch of the system I'm using. I have 1/4" hose from gauge to valves and continuing on to the manifolds. Use a larger hose that fits the fitting on the manifold, and the 1/4" hose fits tight in it so it doesn't leak. If one valve is closed, gauge is reading on other manifold. Close that valve, and open the other valve to read vacuum on second manifold. Here is the type of valve I used. JImChuk
Panel Mount On/Off Fuel Valve, Quarter Turn - Engine & Airframe Accessories (leadingedgeairfoils.com)

[Norm]

I did a carb balance as suggested by Jim Chuck and got the motor nice and smooth. I used a tee fitting and instead of shut off valves as pictured above, I used a set of Welders Vise Grips with the large plate to squeeze each line closed one at a time. Worked like a charm.