Carb sync for beginners

Hi Roger,

I've perfectly mechanically synched my new carbs on a 912 ULS, but each time the idle RPM has been over 3000 RPM, not even near the ballpark. I started with the 1 /1/2 turns in of the idle screw in the manual but the second time backed that off to 3/4 turn based on your advice. The RPM actually went up the 2nd time. The throttle lever the coin cockpit is at idle and hits its stop before starting the mech synch procedure. Throttle levers on carb travel full range and hit their stops equally. Mixture is at the recommended 1 1/2 turns out. I'm not sure what to try next. Any ideas? Thanks

The cause of your issue many times is the throttle system itself. When you open and close the throttle it never goes back EXACTLY where it was before so it looks like there is an issue. About 20 years ago I had a plane that drove me nuts for an hour. I finally did a little research and trouble shooting and found it was just his throttle system. So you can get the sync good once, but everytime you move the throttle open and closed it never goes back to the same exact position. There are so many types and ways to mount throttles there isn't a way to keep track. The one I really like is on The Flight Design CTSW or CTLS. It has a relatively small cable running through the cable sleeve and the carb spring does an excellent job pulling it back where you last had it. The throttle in those planes also have a good cable stop for idle so it always goes back to the same place,

There's a good chance you will have to settle for a tiny variance unless you redo the whole throttle system and then there may not be any guarantees. 

Forget about the cockpit throttle for a second... when the throttle levers on the carbs are in the idle position, can you verify that the throttle valves are actually fully closed?

Also, are the starting carburetors fully off?

I cannot imagine the engine running anywhere near 3000 rpm with both of these closed.