ttmullen

Do you need to run a three line tank with a 4 stroke engine with a pressure line from exhaust to tank (vent)? Can I use three....one from tank to eng, one for filling, and one for overflow? I want to use a slimline f1 fittings, so I just don't know if the 4 stroke will suck good enough without any help from the exhaust fitting. I'm putting it on my funtana X 50. Thanks, any help would be great.........

da Rock

You don't mention which engine?

But, it's usually worthwhile to follow the engine mfg's recommendations. And if you don't have the engine manual anymore, the next best thing is to look at the muffler that came with the engine. If it has a pressure tap, then there is an excellent probability that the engine is designed to use pressure, and very probably needs it to operate as close to trouble free as it's going to.

MinnFlyer

My Feedback: (4)

It depends on the engine. OS engines (With the exception of the new (Within the last year) 91 Surpass will run just fine without pressure. You'll just have to open the needles a little bit more. The new 91 Surpass (That one that has a line from just behind the cam to the intake manifold) MUST have pressure.

I have also run a few Saitos successfully without pressure.

da Rock

so...........

what is your engine?

drone pilot

If you hook the "overflow" to the muffer pressure tap, you have solved your problem. When you fill the tank, and it overflows, it will run out the muffler... EASY NO?

ttmullen

My engine is a saito .80 4 stroke. I have the stock muffler, but want to use just a straight bendable one I have as so it looks better, but there lies my question......Can I use that, and not run a pressure line from tank to exhaust? I just don't want to have to deal with deadsticks if doing this will cause that to happen any more than normal. thanks for all your help....

da Rock

I've no experience with that particular engine but would offer a number of suggestions nonetheless.

I've found that trying to run an engine that was designed for pressure feed without the pressure feed was possible. It was also less than a pleasant experience. It often depends on your intended use. Almost any engine will draw fuel without pressure even if it was designed for pressure. The problems usually come when you put the airplane into maneuvers that create a G-load on the fuel.

Yes, most engines can have their needle valves adjusted to deal with the lack of pressure feed help, but some won't do very well with that ground setting when G-load on the fuel increases. Muffler pressure was developed as a solution to that problem. Back in the days when Control Line combat was cranking up as a popular event, guys discovered that any pressure made the needle settings "hold better" in the air when pulling Gs. They discovered it by comparing the lifespan of engines that didn't have pressure help to engines that did. The engines that did have pressure feed not only held speed and power better in the air but lasted longer before they were worn out. They seemed to be more powerful, but guys discovered they actually weren't. They just lost it when they ran appreciably leaner in the turns.

Guys described it as "not holding the needle setting in the turns". Obviously the needle valve wasn't loosening up. It was the setting not holding up. The Gs made the fuel "heavier" and the engine simply couldn't draw under load the amount it could when the airplane's needle was being adjusted on the ground.

But it depends on the engine. Free flight guys had discovered the same thing and their engine runs were just for one short blast-off climbing run. Some of their engines were much more sensitive than the combat guys' engines. So even back then, it depended on the engine and it's use.

Just how sensitive is the response to pressure from some engines? Well, the combat guys often held high Gs just slightly longer than the precision aerobatics guys. And the stunt flyers discovered that muffler pressure was good enough. But the combat guys stayed with the bladders and balloons (and some of them balloons are pretty stout). But none of them were successful without. And of course, scale flyers seldom bothered. Depends on intended use.

da Rock

BTW, it's actually not really a difficult job to install a pressure tap in a muffler.

If the muffler walls are thick enough, it's relatively easy to drill and tap the sucker. It they're not very thick, it's still easy to drill and tap, knowing it won't be strong enough. You simply use a dab of J&B Weld when you turn the pressure fitting into the thin hole. And you don't tighten it down, you just snugg it. J&B is good stuff. (and it's not a bad idea to always use it even when the muffler walls are thick enough)

ttmullen

Thank you for your time and information. I'll try and do just that, put a pressure line on the new exhaust pipe. I'm sure I'll be able to make it look ok too. Thanks again for your help...

pt19 flyer

My Feedback: (1)

hi
depends on how your engine is cowled and how fully enclosed. a 3 line system is conventient at times when engine is completely cowl and enclosed. just remember to plug the 3rd fill line to maintain pressure. dubro makes plugs for this purpose. the fill line is very convenient for filling and empting. have pick-up and fill line same length in tank and both with clunks. keep pressure line to muffler connected.

I am running a saito fa56 with this set-up

good luck and happy flying

pt19 flyer

ttmullen

thanks for the tips. I'll do just that. I love having all of you here to help with little stuff like this. thanks again.........

MinnFlyer

My Feedback: (4)

I used to have a Saito 80. Be careful not to over-prop it. It took me years to figure out why it wouldn't run right (These were the days before RCU when you couldn't just look up the problem) It turned out that it couldn't swing the 13" prop I had on it.

A 12x7 is about the biggest mine would swing. That's a lot of engine for such a small prop (I swing a 12x7 with an OS 70)

But that Saito 80 finally came in handy one day...

I went fishing and used it for a boat anchor.

mrspiceman

I have a new saito 125. Runs great when I prime it by holding my thumb over the carb & turn the prop. The problem is that I can't reach the carb with the cowl on & am having a real time of getting this thing to run. I know that this isn't the only engine on earth that can't be reached with the cowl on. Can someone fill me in on an easy answer?

MinnFlyer

My Feedback: (4)

What I do is to put the fuel filler on the vent line and give it a few cranks. That forces fuel into the carb. Works every time!

2slow2matter

My Feedback: (1)

Or just open the carb all the way up (with your radio), put your thumb over the end of the muffler, and crank it over. Pressure will feed the fuel into the carb.
If that isn't possible, then close the carb using the radio--kill switch or watever method you use to kill the engine, and turn it over. Not as good as the above mentioned method, but still works OK. Using an electric starter eliminates the need for priming. In fact, I would recommend not priming when using an electric starter in case of hydro lock, you don't want your starter ruining your engine.

o01_10o

Hi People

I'm about to get my first 4 stroke.

I like odd things, I drive an Isuzu VX etc etc so I'm not afraid to be different.

What is the "best of breed" 4 stroke aircraft engine in the 0.5 to 0.7ci size. I'm attracted to Saito and RCV.

Comments please.

Cheers........

MinnFlyer

My Feedback: (4)

OS is #1 in my book for overall price and performance

YS is more powerful, but more expensive - I like them a lot too

Sounds like you might be a candidate for a YS-63

eniac

I really like my RCV 58CD. Mine is in a fully cowled setup, and seems to handle it very well, plenty of power for the GP RV4. The needle isn't even really accesible with the cowling on, I've not really touched it since I setup the engine initially, save for one click leaner on the high needle last time I went to the field. Starting the engine is a nonissue, maybe 10-15 seconds of fiddle/prime/flipping time after fuel is in the tank.

I swing a 12x6 MA wide blade prop, it seems to top out around 10-11K, but after takeoff, its rare to require full throttle.

Just a nod to this engine, its by far the most friendly engine I've used ever.

eniac