os 55ax tuning with pitts muffler

[nguyen]

I have an os 55ax with pitts muffler and I just cant get the tuning right. It runs ok at full throttle and not bad at 1/2 throttle. But the rpm is unstable. At 1/4 throttle and idle the engine really shakes and cuts out. I have tried richening and leaning it and even blocked off one of the pipes. Nothing works. The engine runs and idles nicely with the os muffler. Please help

[eagleclaws]

Got O.S 55sx for 3D flying. I used 13x4 APC props. The problem is, at full throttle the engine seems to quit, rpm slows down. However, at half throttle the engine seems normal. Tried tunning it thru air/fuel mixture but still the same. It was installed with a pitt muffler.

Please HELP

[nguyencuongaa]

It's important to understand that there is a reputation for glow-engines to be difficult to tune. This is a common error in thinking. With a little bit of know-how, tuning a glow engine can really be a simple, pain-free process. People that don't properly understand the basics can easily become frustrated by what should be a simple, straightforward process. Here's how you do it:
Glow Engine Tuning

[Texastbird]

This tuning guide is completely ignoring types of fuel used, glowplug heat range and there is also more than one type of carb. If you have trouble with an engine with a pitts style muffler, I usually suspect that it may have too little back pressure. Its not unusual to have to block off one of the exits on a dual outlet pitts. If you are running too big a prop, the engine will slow down as it overheats. Try a smaller prop and see if the engine runs more consistantly.

[fastace]

example ; the OS 55 AX is very easy to tune with its stock muffler. what happens when the pitts muffler is fitted is back pressure problems arise, i found this out when i was setting up a GP Revolver and many guys did say its the pitts muffler and there are 2 cures; one is buy a different type that has smaller and longer outlet pipes or the simple fix is to add the next size down exit pipes that fit inside the existing pipes , also make these a little longer. by doing this mod to the pitts you will get more engine back pressure and the engine will run alot better.

[WaterLogged]

	Quote: Originally Posted by fastace
	example ; the OS 55 AX is very easy to tune with its stock muffler. what happens when the pitts muffler is fitted is back pressure problems arise, i found this out when i was setting up a GP Revolver and many guys did say its the pitts muffler and there are 2 cures; one is buy a different type that has smaller and longer outlet pipes or the simple fix is to add the next size down exit pipes that fit inside the existing pipes , also make these a little longer. by doing this mod to the pitts you will get more engine back pressure and the engine will run alot better.

You wouldn't happen to have a link or a little more information on how to perform this mod would you? I picked up this motor with a slimline q series as a gift from my job without doing enough research on the pitts. It's for a Fall/Winter project, so I won't be able to confirm the power loss (if any) until next flying season. But I might strap the motor on another plane just to get it broken in and tuned this season. Anyway, any help would be appreciated. Thanks!

[alfycat]

This is another great option: http://www3.towerhobbies.com/cgi-bin...&I=LXDG59&P=ML

[ThumbSkull]

Measure the exit port on the stock muffler and just make the pitts combined port area the same. Usually it is easier to close off one port and make the other one the same size as the stock port.

[3Dguy]

I've got no problems with my 55AX. Using a Bisson pitts muffler and APC 13x4W prop. Slow, reliable idle, smooth transition, and strong top end. Backpressure is also normal.

[ThumbSkull]

It's be worth knowing how it runs on the stock exhaust. May still be a rich low end.

[fastace]

	Quote: Originally Posted by WaterLogged
	You wouldn't happen to have a link or a little more information on how to perform this mod would you? I picked up this motor with a slimline q series as a gift from my job without doing enough research on the pitts. It's for a Fall/Winter project, so I won't be able to confirm the power loss (if any) until next flying season. But I might strap the motor on another plane just to get it broken in and tuned this season. Anyway, any help would be appreciated. Thanks!

to do this mod to the outlet pipes only requires 2 extra lengths of alloy tube that fits inside your existing pipe outlets, use a heat resistent sealant to fix these into the muffler pipe ends and have them approx 1 inch longer than the stock lengths.

[WaterLogged]

	Quote: Originally Posted by fastace
	to do this mod to the outlet pipes only requires 2 extra lengths of alloy tube that fits inside your existing pipe outlets, use a heat resistent sealant to fix these into the muffler pipe ends and have them approx 1 inch longer than the stock lengths.

This sounds like a great idea. Any idea where I can find the alloy tubing you speak of? Would my local hardware store have such a thing or would I need to go to a specialty shop or pick something up online?

Thank you!

[Dewayne Vaughn]

K&S used to sell it. Check with your hobby shop.
alloy tube = aluminum tube...although it could also be brass or bronze or whatever... it's easier to use similar metals.


Luck, Dewayne

[WaterLogged]

My local hobby shop has a K&S display with all sorts of tubing. I should be covered when I go through with this install.

Thanks!

[jesknow]

Why does this always happen to me? I wonder why it is all the fixes I find on the web are exactly for the opposite of what happens to me. I have a new just broken in OS55AX with bison pitts muffle specifically for the OS55AX and even when I lean it to the highest pitch rpm, when I hold the nose down she floods out. I use a 10*8 apc and 10*7 wood cause I'm into speed not so much power. I hope you find the answer to your problem man.