Hey guys...I need some expert advice here. I picked up a used plane/motor deal and the motor is giving me fits. Unfortunately, like with most deals, I have no actual history on the motor. It is a nearly new Zenoah G-26, ..maybe just a couple of gallons of fuel through it... the piston appears shiny and clean, like new,...standard Zen' stock muffler, 40:1 fresh Amsoil oil/fuel mix, APC 16-8 prop. Here are the symptoms of my problem. It is very difficult to achieve a good prime for starting. I must use an electric starter and I must spin the motor...fully choked and wide open throttle, for perhaps a full minute before fuel is up and she is ready to fire. That's quite unlike any Zenoah I have ever run. The fuel plumbing is Tygon, with no air leaks, and the tank is on line with the carb, and positioned just about 5 inches in back of it. Once running, the motor seems to be OK...on the ground! Idle is around 2200, full throttle is 8600RPM, transition is great too, however, I am unable to shut it down with the throttle alone. I must use the ignition kill switch, and I have (2),...a manual switch on the fuse, and another on a servo operated remotely from the Tx. ...a very handy item to have!!!
After take off, things seem to change. The top high end is OK...I cant tell much difference there, but as soon as I begin to reduce throttle, the motor RPM drops dramatically....much more than what would be anticipated by the minimal throttle stick movement. Mid range, if you can call it that, sounds like it may be much too rich, but it is so weak and unreliable, I have not flown much at that throttle setting. Idle in the air is non-existant....it will immediately go dead if the stick is brought back to the idle position. Challenging, but not much fun.
The carb shows some signs of having been worked on...at least the original stock throttle lever and spring were removed...I guess to accomodate a different (nose-wheel steering arm) type of throttle connection. I added a black plastic velocity stack on it, (the kind you see on the Walbro Go-Ped carbs) which does prevent fuel mixture from spilling out and messing up the side of the fuse. This fuel "saving" did make it run somewhat richer, but a 1/4 turn on the low needle seemed to totally correct that issue. Other than that, the stack doesn't seem to make any noticeable difference to the running of the motor. So....do I have a defective carb or what? Thanks very much for your comments.
Jim