Here is the latest update on my balance tube installation.
When I installed the balance tube adapter blocks I had to move the carbs back toward the firewall 2". The throttle cable holes in the firewall weren't perfectly aligned with the carb brackets during the airplane build, but worked well. Now that they are closer they were more out of line and did't work as well. I made a couple of bulkhead fittings and enlarged the holes, biasing them towards the correct position. Now the hole is much smoother and will not chafe the cables and, being closer aligned, the throttle moves perfectly. The installation required me to completely unhook the cables and re-install requiring a carb sync.
The required sync allowed a perfect opportunity to do a "balance tube test". With only a rough mechanical sync and the balance tube installed I started the engine and warmed it up. I noticed how smooth the engine ran and idled. I then removed the tube and fitted the new adapter plugs in it's place and hooked up the gauge manifold I had made years ago. The engine ran extremely rough and would barely idle! Fuel was flying from the vent tubes. I shut it down after just a few seconds.
I'm here to tell you that this invention of Bill's WORKS!
I then did a careful carb sync just like Roger recommends; i.e. at idle and 3500rpm. This is so it is tuned perfectly from the start. The balance tube is there for smooth running. The test flight, after re-installing the balance tube, resulted in absolutely smooth operation at every throttle setting from takeoff through landing and taxi. During this flight I started with no limiters on the throttle arm and added -4 washers until I still had 5200rpm in full climb with no sign of engine miss. I ended up with 4 washers installed behind the knob. Even with limiting the throttle I still get the same RPM as before the balance tube.
I am really happy with this mod. Thank you Bill! Thank you to everyone who commented and made suggestions about this installation.
Alan
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