I have a spring on the Zenith throttle shaft that will pull WOT if the throttle cable breaks. That WOT spring was keeping the butterfly slightly open and not closing fully at idle. Verified operation by loosening the Bug Nut for the Bowden cable on the carb throttle arm: The throttle goes to WOT and stays there. So now there are three springs on the throttle butterfly shaft and everything works fine.
Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA ------------------------------ Years ago I took my Grumman TR2 to get it's annual inspection. The carburetor was rebuilt and I flew it about an hour when the throttle arm came unhooked in flight. If the carburetor had been spring loaded to go to idle, It would have been a very bad thing. However, the carburetor was spring loaded to go to wide open. I flew back to the airport, made sure runway was made, and mixture control to cut off. I was so thankful that day that the carburetor was set up that way. Now I am building this Rotax 582 bird that has two carburetors with springs set up where if I have a throttle cable failure it will go to idle. Bad design and the thought of it makes me cringe. I realize there are a lot of them out there flying all over the place, but that design is wrong for aircraft. Failure mode should be the safest mode....wide open. Kevin Golden Harrisonville, MO Streak Shadow ---------------------------------------------------------------------------------------- In a message dated 6/20/2013 9:00:46 P.M. Central Daylight Time, smwood at md.metrocast.net writes: Finally got my Zenith carb adjusted on my 2180 VW to consistently and reliably idle at 700 RPM. I found that the torsion spring between the butterfly shaft and the throttle arm was not strong enough to return the shaft to the full closed position. I added another extra tension spring from the bracket on the shaft to the throttle arm. Playing with the mixture control from the cockpit while the throttle is closed, I can get idle speeds down to 550 RPM. Don't want to be there - the engine still runs, but is about to shake the plane to pieces. 700 RPM is much smoother and the 4 straight Dragon Fly pipes sound great. Still have to be careful to slowly advance the throttle out of idle or the engine will cough once and die. Above 1000 RPM I can snatch and punch the throttle any which way and the response is quick and positive. Yes, I used an electronic tach checker to verify the Grand Rapids tach readout. I am betting that landing roll outs will be much shorter now. Now, on to fixing the high oil temps. Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA
