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Old 03-11-2008, 02:12 PM
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the Gnome
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Default RE: Everything Radial Engines

Hey Woody, sounds as if You were doing right till now, 21x9'' seems to be ok, and 6900 confirms this, You are not lugging the engine. Your venturi size seems to be ok too. I think, as radials suck their mixture through the crankcase, differences in mixture quality can only be felt with big delay and sometimes, small differences, as between correct and a small ammount rich, can't be felt at all. This makes adjusting a radial a bit difficult, even on my ST710 Seidel I can only tell the right main needle setting by testing the upper mid range load / revs, at full throttle it's very difficult to feel a rich mixture and absolutely impossible to find the correct needle setting.

You seem to be advanced radial user enough to set the carb right, so I'm affraid there is no other advice than to test plugs of different heat, on my Seidel ST540 colder plugs cured some similar problems. The most signifficant effect was, that, when pushing the stick to full throttle, revs got to about 6500 and after about a second dropped some 500 to 800rpm. If You can find a similar effect on Your 400, may be a too much advanced ignition timing is the basic problem. When the engine gets warm or hot while flying, this may cause even worse engine behavior.

What do You think?

gnome

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