Hey,

It has been a good while since I posted about this, and it can really cause you some problems; especially if you are new to gasoline engines, so I am going to mention it again.

With the rotary carbs common to most all glow engines, a little slop in the throttle linkage, while not good practice, wouldn't normally cause a lot of problems. However, with the butterfly throttles in our gasoline engines, (Walbro, Zama), slop in the carb linkage can cause big problems.

I had this happen to me a few years ago, and it caused me some "head scratching" until I figured it out. If the linkage on a butterfly type carb is not completely slop free, the engine "vacuum" will try to draw the butterfly closed. So what can happen is that you look at your carb butterfly during your radio setup, and see that it is right at full throttle when you want it to be, so you call it "good to go". However, if there is slop in the linkage, through a bellcrank setup, loose linkage, or whatever, when the engine is running it will partially close the butterfly when you "THINK' you are at full throttle. This will screw up not only your high speed mixture adjustments, but also overall power! I would even go so far as recommending that you tune your EPA (end point adjustment) for the throttle with the engine running and a tach in hand to avoid this problem. Just have someone there to help with the "juggling act" for safety.

Just thought I would pass this one along again. I bet there are many setups out there that are less than optimum, due to this problem.

Keep flying!
AV8TOR

You are probably right. Same goes for idle adjustments. On several occasions unreliable unstable idle rpm could be traced back to the linkage.

YUP...That is exactly what I told my flying friend, he can never get RPM to return to the same exact idle speed, which is needed for his airplane and the way he lands!!! Capt,n