I fly an avistar with a tower 46 pro. The other day I was flying and when I brought the plane in for a landing I noticed the muffler bolts had loosened up. I also noticed that the plane ran better with the muffler loose. Tha rpm's went up on full throttle, and it ran smoother. why did this happen. I did tighten the bolts back up and continued to fly but, why would the engine gain rpm's and sound better with a loose muffler.

You may have too much back pressure.
Try taking the baffle out and see if that's
what you want. Some motors run better
with less pressure and some don't.
Hope this helps.

Doug,

Well this is the point!
The Tower/Hobbico .46 silencer is 'semi-tuned' and does not have a baffle of any kind.

It adds RPM, when compared to a standard OS 783 silencer, for example; even if the OS' silencer had its baffle removed.

But maybe when compared to open-exhaust figures, it is still just a restrictive muffler, not a real tuned-pipe.

But just getting the bolts loose and having some of the back-pressure escape from the joint, does not constitute an open-exhaust situation in my book...

Good point. I had forgotten about the "tuned" muffler.

I have that engine, but I have a different problem with it... It runs like crazy level, but if you point it straight up, it always craps out... Even if you adjust the mixture with the plane pointed up it doesnt work quite right. (I met someone else with the same engine and same problem) I suspected that it was the tuned muffler not creating enough back pressure (plan to try an OS muffler and see if that helps) Im Interested to hear yours ran better with less pressure.

I have a Tower .46 and am very pleased with it. Break it in properly and it will run great. Point the nose of the plane straight up at full throttle and adjust the needle to max rpm. Should be fine in the air.

Mike

Mike,

....That is, max minus 150 RPM.
If not, it will lean out as fuel level goes down and when the engine unloaded at speed.
This is not too good for any engine.

I think when the muffler got loose, you just went lean and that was the reason for Higher RPMs.