Idle Speeds and Carb Sync

First do a mechanical sync using a .004 feeler gauge. A mechanical sync only gets you in the ballpark, but it will get you closer for your idle adjustment. I know the book says 1.5 turns in for the idle stop screw, but I find that idle too high so I only use 3/4 turn in. If your using a Vernier throttle don't use the stop plate on the carbs to stop the throttle. You will bend the idle stop screws and then the engine will quit. Install some cable stops on the throttle cables where it meets the Bowden cable adjuster.

Thank you for the reply Roger.  When you say 3/4 turn your talking about 3/4 turn out after running the idle mixture screw all the way in?

Mark Keiper wrote:

Thank you for the reply Roger.  When you say 3/4 turn your talking about 3/4 turn out after running the idle mixture screw all the way in?

No. The mixture screw on the bottom is turned out 1.5 turns and then leave it alone. It should never need to be messed with. It will stay put. 

I'm talking about the idle stop screw up on top. The one you turn to make the idle higher or lower.

If you are over 600 hours and have no indication that a proper carburetor inspection (involving removal and disassembly) has ever been done, I strongly suggest you get that done before you attempt anything else!

Mark,

The video on how to balance can be troublesome because it does not demonstrate how to address your situation. From your original post, I gather that you did all your off idle synch adjustments on one carb only and you increased the engine rpm using that carb to balance. Then you tried to lower the now too high idle using the idle speed screws. If this is correct, then this is why you are where you are and you need to start over mechanically as Roger recommends, and this time, adjust the off idle on both carbs to balance (e.g. increase rpm on one carb, decrease equally on the other). When you come back into balance, if your idle speed requires adjustment it will be minimal and you will use the idle speed screws, not the mixture screws, to raise or lower idle speed to the recommended rpm (remember to adjust both carb idle speed screws equal amounts in the same direction when doing this, make small adjustments) and you will be fine.