PROBLEM SOLVED!!

Short story...
Removed the muffler baffle and the vent line no longer gets plugged.

Long story...
The engine's owner had sent the engine back to Horizon where they replaced a bearing (inner race spinning) and did something else--a gasket or something. They returned it and said the engine was running fine.

The engine owner came out to fly Sunday (1/27/2008) when it was about 20 degrees F. We made sure the vent line was clear before starting the engine. We started the engine, it ran about 10 seconds at full throttle, leaned out, and stopped. The vent line was now plugged.

We cleared the vent line (blew hard) and removed the muffler baffle. We tuned the engine and got two flights in without a hiccup.

I hope that someone from Horizon reads this and can determine if there is a flaw in the muffler baffle design--especially for cold weather flying.

--Doug