I've been running Stalkers for years with great results, and find them to be very good stunt engines. they are well designed and made using very good metallurgy.
I suggest you not run Castor at all but, rather run straight FAI fuel with a good modern Synthetic oil. In all my Stalkers, over 20 years of use, I've never felt the need to run anything else but FAI fuel.
Nitro is not needed in almost all cases.
Castor, If you absolutely believe you need it, should not be more than 3-5%. Too much castor can carbon up your engine requiring de-coking, to remove it periodically.
Start with an 11 through 13-inch prop at 5"- 6" pitch, 6700 - 8+ K RPM for a start, is usually a good bet. Mine wind up somewhere in that range.
I shy away from running long props on my .51's and, I get great service out of an 11" X6" prop with that engine. As you likely know, they haven't made the .55 for a long time but, with my.61, from the same time frame as yours, I use a 12" dia. prop. I do use a 13" prop on my .81's. My engines seem happy with these prop sizes, so I run them that way. There are also fewer problems with prop Gyro effects with the smaller propellor diameters in my opinion.
Hope this info helps, best of luck with your Stalker .55
John Miller
Topic: Stalker 55 (Modusa type) 2-2 mode. (Read 1321 times)