K&B 48 RICH AT NOSE DOWN

[carddfann]

Hi,
I have a K&B 48 with stock muffler on a Sig Kougar. It runs good level and when I pick up the plane and tilt the nose up.
When I tilt the nose down, the engine runs a few seconds and quits. Usually, this indicates a too rich setting, but it already
seems lean enough. Fuel is fresh, 10%, synthetic/castor blend. K&B glow plug looks good and glows hot. Tank position is
good relative to carb. I'll try cleaning the carb in case there's contamination or old oil residue from last run (hasn't been
ran since last year). Any suggestions what else to check? BTW, I bought this engine from Mecoa - not Ebay.
Thanks,
Gary