My ZDZ80 starts fairly easily, and runs ok, but it sometimes quits when I give it quick full throttle (usually, on the ground when I'm heading out to the runway for a flight). This would make me think that it is a bit lean on the low needle, but in the air, it gargles every once in a while at mid throttle like it is a bit rich. It does not stop running when I goose it in the air. Any ideas why this might be happening?

when u do it on the ground is this only on a cold motor?

Good call Krazy, sounds like it's just not warmed up yet.

Is the engine warmed up and at operating temperature when you are taxiing out? a bit lean on the low end can cause a transition problem on a "cold" engine, but it will go away when the engine is at operating temperatures, I guess it won't be considered lean at that point.

It is also possible that the diaphragm in the carburetor is getting some air pressure on it during flight causing it to go a little rich in the air, I had this condition on both of the rear carburetor engines I have, both were under a cowl.

Thanks very much for taking the time to respond guys. I thought it may have been a cold engine, but it happened on the second and third flights of the evening also. I should have tried to gun it on the ground after the flight to see what it would do. I'll try that next time out. If it persist I thought I might try the new WJ71 carb I just bought for a spare engine. Also, what are the symptoms of a bent crank? My spinner looks like it a has slight wobble when the engine is running.

never gun a cold engine. Thinking of that, never gun a gas engine ever unless the carb has an accelerator pump! I would propose to use a 0.3 second servo delay on the throttle stick just for that matter. Smooth throttle application does not have to mean the prop spools up slower. It spools up more secure. That is fact.

A bent crank will shake your plane apart, or at least impart a bunch of vibration, the amplitude of which isdetermined by the severity of the bend. The part that the spinner cone is bolted to is not the crankshaft but rather a pilot shaft screwed onto the crankshaft, it could be bent itself or you could have a spinner that is out of whack itself. The pilot shaft is actually shipped un-installed with instructions on how to install it.

Jody,
I'm glad I included the question about the crank shaft because now I'm pretty certain that the shaft itself is ok...the engine runs VERY smoothly. The plane vibrates very little. I may check the threaded part to see if it is bent, but I don't think that is too big a deal if it is. Thanks for the great information.

Pi Reivers,
I don't gun the engine in flight because I like to fly smoothly, and in a scale like fashion. On the ground however, I like to give quick throttle bursts just to make sure the engine is properly tuned, and running tip-top. Good, crisp throttle responce sure gives me confidence that I have the engine set up propertly. Once the engine is completely warmed up I can't see how that would do any harm.

That is what we all do. I have a delay programmed in, and am ready to go if the engine responds well.
A well tuned idle will hesitate to respond to throttle when the engine is still cold. I need to hold idle for about 1 minute before I can go to faster idle for another minute. Then the engine is warm enough to go fly.  If the warm engine will still hesitate ever so slightly, the engine will run smoother down to lower rpm. This tuning however can cause flameouts because most Walbro carbs have no acceleration pump. A delay in the trottle channel will help you set up the carb better and it will prevent flameouts. If with delay the warm engine still stumbles you know you have crossed the line.