Read the thread on Saitos and their "ugly" mufflers. I have been running my Saito 72 w/out the muffler for one season now and have not had any problems. Does anyone else do this with their 4C? It is a little louder (but sounds good on my P-51), can hardly see the header pipe where it exits the cowl (looks great this way). Will this cause any long term problems with the engine? On a side note, this thing runs like a top this way, very low idle speed and runs very smooth on the high end. No need for the pressure line to the gas tank, it seems to draw fuel fine without it.

Old 4-stroke engines came without muffler, just the header pipes. They were a little loud. I had a Saito 45 which also came only with header pipe. Some early YS120s also without muffler.
No problem with that, but I would use muffler just to keep the noise down.

Saito make a new header pipe with a welded pipe off of it for your pressure hose. I have one on my Saito 56 and it's not that much louder.

I personally like the louder gruff 4c sound it makes. Just right for warbirds. I guess I will keep running it this way since it doesn't seem to be harming the engine performance at all. I think it's kinda funny how people get concerned about where to put the muffler, just leave it off, it really isn't so loud that it would be a noise issue. Plus you don't have to worry about losing it during a flight..........and it doesn't ruin a beautiful cowl this way.....try doing that with a 2c!

A friend of mine has been running a YS 1.40 for several years now without a muffler. No harmful effects that we can see.

The YS engines don't use muffler pressure to their tanks, (they use crankcase pressure to pressurize the tank and a fuel regulator instead), so they don't "need" a muffler at all other than to keep the nosie down. Like the others above, I found that many of the early four stroke only had a straight pipe with no pressure tap (my Enya .60 four stroke is this way) and they ran fine on just carb suction. I think the fact that many of them also have pretty conservative carb throat sizes also helps create good suction/fuel draw, even without muffler pressure.

Lee

I would suggest doing one thing after you stop the engine - turn it over slowly by hand until you feel the compression resistance. This will put it in position with both valves closed (seated) which allows the excess heat to be conducted, closes off the ports to dirt and bugs, and helps to keep your valves symetrical and takes the load off of your valve springs. The alcohol gokarters do this religiously.

That's pretty good advice, setting one up at TDC when sitting, never thought about that before!

Hi.
Can I fly an OS 120 4-stroke III just with the flex pipe attached and without the muffler at the end of it?

Thanks:
Daniel Maia

Sure, if your field allows it. Some don't because of the added noise. It won't hurt the engine as long as you have a "header' on the engine.

Some fields have already been shut down because of noise complaints, so use your best judgement when running an engine without a muffler.

As Danny says, You have to have at least short pipe on it.

Enjoy,

Jim