I recently bought a big Roto 4 stroke for my 1/3 scale cub, and its a work of art. After receiving the engine and getting a number of emails from roto about my concern of "what oil" must be used for this engine. My question is do I have to use motul 710? I have always used stihl ultra hp for everything, but from what I get from them is that they only guarantee the engine if you use "their recommended oil" I mean I can switch to motul but stihl ultra is right down the street from me. thanks for any input.

Well, I use Stihl HP Ultra myself and I am quite satisfied that it does the job. I am pretty sure that the Motul 710 oil would work well too. If you are concerned about the warranty then using the suggested oil is good. If that is the oil they say you should use, then it is probably best to stick with it.

But over the years I got to the point where I feel there is no warranty from the manufacturers anymore, so I usually don't bother even trying to get a warranty on something anymore. They will look for any excuse to get out of honoring a warranty problem anymore. So I would have used Stihl oil myself if I had the engine.

What ROTO is it? The 85cc twin or the 170 quad?
A friend of mine had the 85cc installed in an aerobat and he had some problems with the fuel supply, as the engine would quit from fuel starvation once in a while. But adding a fuel pump cured the problems completely.
I guess it had the same problems with the internal pump as the Moki radials does, where adding an electric fuel pump works wonders on the engine.

Yes it's the newest version of the roto 85 fs-ng. Supposedly they fixed the problem they were having before with the fuel not pumping to the carb. I'll test run it while it's on the airplane just to make sure everything's up to par. I've been thinking a lot about what oil to use and I'm thinking of going to motul 710 over Stihl ultra hp. We'll see

I'm in the middle of installing the roto in my 1/3 cub and I was wondering what you guys do as far as a air filter? Last night I cut a circle out of a speaker cover and silicone it on the end of the velocity stack. People don't realize that wood/balsa can be sucked in the engine as well as servo screws if they come loose. I'm just curious what you guys did. thanks

Well today I fired the new roto 85 up and I wasn't impressed at all in the beginning. The engine was having issues like it was too lean and when I richened it up it was running real rough, so after fooling around with the needles and nothing was really doing much I noticed I put my fuel tank on the floor of my cub so I ran in and got another tank and sat it on top of the fuselage in front of the windshield and waa-laa it ran really good, so I guess you really need to have the tank a little higher than the carb so now I'm in the middle of relocating the tank higher in the fuselage. I remember when the os120 would do that if you didn't have the tank just right.

Four stokes use pulses in the intake for pump action, much weaker the two stroke crankcase pulse pressure. Some uses have installed electric pumps to cure their problems.

Well I finally got around to firing the ol'e engine up after I relocated the fuel tank up higher, which now is slightly higher than the carb. When before the tank was lying on the bottom of the fuselage causing the engine to bog , and lay down and so fourth, but when I fired it up today it ran like a Swiss watch! No bogging, no hesitation, it just ran perfect and sounds really good! I'm happy with it and glad I bought it.