[szicree]

I'm finding that the travel on my Vans mixture cable doesn't quite take my mixture from stop to stop on the carb. Will this be an issue? Thanks.

 

[Tom Martin]

Steve
Yes you absolutely need full travel on the mixture. You need full rich for high power settings and if you cannot go to idle cut off you will not be able to stop the engine with the mixture. Chances are the fault is with your quadrant as many of them do not have the holes placed in the right spot. There is probably enough room to drill a hole higher on the arm at the quadrant. Another options would be to shorten the arm at the servo.

 

[szicree]

Nope, not the quad. In fact, I can disconnect the quadrant and slide the cable back and forth and come up just short of full travel. Hmm?

 

[steveciha]

Steve,

I had this happen on both the throttle cable and mixture cable that Van's sold me in their firewall forward kit about 5 years ago. In each case, the cable was perhaps 20 thousandths away from hitting both the high and low stops. I called Vans about it and their answer was to drill another hole in the throttle arm of the carbureator. I thought that that was a stupid answer and never did it. I believe that they had a batch of control cables that were made just a little bit too short. I never changed these cables and my engine operates fine. Idle cut off stops the engine and at full rich the cht's are OK and the fuel burn indicates that the carb is at or very near full rich.

I had a real particular FAA inspector and he told me later that he almost flunked my plane because of the control issues. Ideally the push pull knobs or quadrants should not go all the way to the stops. The stops on the carb should make contact. He told me that if the rest of the plane had not been as good as it was it would have become an issue. He further told me that in all likelyhood the controls will work fine but he still recomended changing them. To this day i have not had any problems.

steve ciha

 

[asav8tor]

If the lever control lever or push-pull knob is hitting the stops and the lever on the mixture/throttle is not, then it is not the case that the cable is too short.

It is a simple geometry problem and yes the solution is to move the atch point closer to the pivot point.

I think you are kind of lucky not having a problem without the mixture being able to hit the full rich stop. There are many possibilities why it's working on your installation, however it's not good advice for everyone to try it. Someone will experience engine damage on another install.

Important to hit the full rich stop (on the carb/fuel servo) when the cockpit lever is full rich!

 

[szicree]

I think there may be some confusion here regarding these cables. There are actually three stops: the one on the carb, the one on the quadrant, and the cable itself has an internal stop. It is this stop that is causing the problem. I'd modify or replace this cable before I start drilling holes in my carb.