ORIGINAL: safeTwire
A similar event like the gentleman above described: After being run well on a bench, an inverted 91, would not idle correctly AT ALL when in the plane.
Reason : Because the tank's output was at least one inch higher than the carb's inlet ( viewed/measured as the plane sits normally on it's gear) , I failed to accept the fact that this ''might'' cause problems...
It really does NOT cause problems.
You would never be able to throttle down, with the plane in any position other than level if tank height was so problematic to idling.
In a nose up situation a typical ARF has the fuel a good 6-9 inches below the carb's inlet, yet it will still idle just fine once the engine is PROPERLY tuned.
No, the only reason to worry about this is to avoid siphoning while the engine is NOT being used ( e.g. the engine will fill with fuel ).
One started it's not a big issue.... PROVIDED your PLUMBING is OK.
If your engine does not idle when on the plane and your attempt at adjusting the tank height seemed to have cured things, then it is MOST likely that you solved a minor flow or plumbing problem while you were at it.