I have a Brison 2.4 and I have a question concerning the mix settings. When I fly at half throttle, the engine sounds like it is 4 stroking. It doesn't die, just sounds funny. I don't want to take the chance of making things worse. It idles great and I get about 7400rpm with an APC 20/10. I will fly this way forever but if I may have a potential issue, I would like to address it now.

Why, it is 4 stroking. As long as your idle and top end are correct, there isn't a whole lot you can do with the midrange without changing the carb or the timing curve.

The only thing you could do with the timing curve is have it where you have to run faster before it advances fully. And you can't do much with that either.

As long as it don't quit, does it have to run perfect all the time?

Two cycles are bad about four cycling when they are not loaded very heavy. Apparently the motor makes a lot of power at this rpm for the prop load that is on it? The only thing that retarding the timing at mid range would do is to have it make less power to where it is puilling harder.

Enjoy,

Jim

If you have the room get a walbro ( model wy) for your Brison engine. The advantage of a wy is that they give a very even air/mixture throughout all throttle settings. These carbs are a little bigger, so you may not be able to use it in your cowl setup. I bet you are flyng a scale plane at lower speed and the engine does not sound good at those speeds. Thanks Captin John P.S. you can get a Walbro service book, that shows operation and how to tune or rebuild the carbs. Very nice book. Phone 517 872-2131

G-ware: You can also try a prop that will load it down more at the speed you want to fly.. Good Luck Captin John

If you are running the engine inside a cowl you might also want to try venting the carb diaphragm inside the fuselage. How this diaphragm moves has an effect on mixture and cowl pressure may be screwing it up. The diaphragm now vents through a small hole in its cover, its not hard to install a nipple and a hose, might be worth a try.