The O.S. Wankel engines can be mounted with the carbs in any orientation. Up, down, sideways, angled...the engine doesn't "care".

If the carbs are mounted below the centerline of the tank, fuel will siphon form the tank to the carb once the fuel line's filled. This will happen with ANY engine. With the Wankels, it happens a lot because many modelers have the centerline of the engine centered on the cowl, which also happens to be near the centerline of the tank, putting the carbs well below that...sometimes lower than the tank bottom.

As with any other non-pumped engine, the Wankels need to have the fuel tank mounted so that the centerline of the fuel tank goes throught the centerline of the carb, or no more than about 3/8" lower.

The O.S. Wankel will tend to start better if it's primed so that it's a bit wet. Use a fuel with about 20% oil content and 5%-15% nitro. We'd strongly recommend a high-castor content in the oil package. If the engine is under-oiled or over-heated, the apex seals will go and the engine won't have enough compression to run. If the rotor housing gets scored, the rotor, the housing, and the apex seals all need to be replaced.

You MUST use the O.S. Wankel glow plug to get proper operation.