In the just concluded flying season. I had a lot of trouble with an OS 75AX inverted on a Phoenix Topstar. We tried every possible config: with baffle, without baffle, rich setup, low end screw adjustment, high end needle adjustment, with nitro, without nitro etc. But we couldnt keep it running. Initially, it would cut-off in the hover but later on it began to cutoff even in level flight if it was run at 50% for one circuit. Cooling is not an issue as we were running it without cowl. When I was flying without nitro, I got it stabilised with the baffle installed but it couldnt sustain the hover and I had to try nitro to help out in that. All along I am using fuel with 20% normal castor.

Now for this season, we will be installing it at 90 deg. Some othere on my field with inverted engines also have had the same issues and they will also be doing the same.

My concern is that in my new reactor, if I put in a 2Stroke engine: the 55ax (I have a old workhorse that has never given me issues) I will have to install it at 180 or 225deg, I dont want any issues with it. What I want to know is, is it that the 2strokes cannot be mounted inverted? If so, I am better off going for a 4stroke OS FS 70surpassII / 70Alpha / 81alpha. If not, I would prefer to install the 55ax as its lower weight and fewer moving parts will give me a lighter wing loading that will be better for 3D.

I know that I have raised this issue before in the various forums but I am raising it again as I have not received a satisfactory answer to my query.

Ameyam