Hello Everyone.

Im happy as I have been able to have much more power out of my 33cc Mitsubishi conversion taking out the muffler and making my plane much more fun to fly

Anyhow I dont have such a stable idle and transition compared to the one I have when I have the muffler on.

Does the muffler have an effect on carburation? I thought not as it was not pressurizing the tank but seems Im wrong.

Generals of my engine are

- Mitsubishi TLE 33cc
- Original muffler gutted with 2 outlet tubes - Now flying without muffler and get arround 500 RPM more
- DLE 30 cc carb on it (Haven´t opened the manifold yet)
- Spinning a 18x6 Turnigy prop at 7,000 RPM (flying at 2,240 meters over the sea level)

Thanks everyone.
VĂ*ctor.

When you remove the restriction of the exhaust, it will lean the engine out. The carb will need to be retuned and richened up a bit. A GLOW engine will idle and transition better with a bit of muffler pressure because it helps keep the glow plug hot at an idle, but a gasoline engine does not need any back pressure from the muffler at all. Power can be increased by using a tuned pipe, or expansion chamber, but that is a different subject entirely. Some people think a gas, ignition engine needs some back pressure, but it is simply not true.

AV8TOR

What do you think a tuned pipe does...??
If not create a back pressure wave then maybe a few books need to be re-written.

A tuned pipe creates a resonant wave that helps evacuate the exhaust gases, and then a reflected wave helps close the port at the correct time. This is all time critical in relation to port timings, rpms, etc., and generally only works well over a certain, and often small rpm range. This is quite different from back pressure from a muffling device which only reduces power.

One of the tests when tuning an expansion chamber, or tuned pipe, is to record the open exhaust rpms. Then you can start tuning the pipe length and realizing a gain from its unique characteristics. It does not work by back pressure, it works by sonic waves. Indeed, if the outlet on a tuned pipe is too small, it will cause an engine melt down in quite a hurry.

AV8TOR