Hi Guys, hope you all can help me here. I have a Minicraft (Hangar 9) cap 73" powered by a Moki 135 turning a 18 x 8 Bolly wood prop. This engine / prop setup seems perfectly matched to this plane, unlimited vertical and most manouvers usually only require half throttle. Here in lies the problem.
The motor starts easily, idles very well, excellerates to full throttle without hesitation BUT while flying and the throttle is returned to half throttle it gets a real burble up, sounds like a miss but it does not cut out, sounds like it is going to but just keeps on flying well. Went into panic mode the first few times it happened as we thought we were in for a dead stick landing.
When the stick is either moved to lower or higher position the motor responds instantly and loses the Burble. Any ideas, Please????

I think I know the sound you are talking about. Its not a pop sound but a burble that keeps going if at a certain throttle setting. I had this sound on my Moki and it concerned me at first but it was determined to be ok. It wouldn't make the sound on the ground right? Your engine sounds fine to me. Just make sure you check the low idle "disk" every couple of flights and make sure it doesn't move on you. It sounds like you have a happy and strong Moki. Just make sure you are running a bit rich. When a Moki runs lean or hot it will die quickly, without warning.

hope this helps

You might want to lean out the idle disc a hair. Try to reach a compromise between best idle and cleanest midrange. Also, if you are not using an OS F plug, try one.

Jim

Hope you're not using too much nitro. Take a tremendous amount of time to break in as well

Thanks for the help so far guys. Manfred I am using 5% Nitro, what do you think, too much or should be ok?? The motor has probably only had 6 litres of fuel through it. I will try the os F plug, currently using a K & B plug.

Thanks again, I welcome any more advice.