Sound like a cold fuel problem?

Needed to run out yesterday when it was 21 degrees F out, snow on the ground. Went out to truck fired her up, easily as always, let her idle for a minute to settle down then hit the high idle switch. Upon high idle the engine would make a stumble every 6 seconds or so, kinda like a quick cut off that lasted less than half a second. Since I was standing outside, while snowing, in bare feet and shorts, I left it and went inside. Came out 5 minutes later and she was purrin pretty at 1070RPM (high idle). Figured it might just be a cold fuel thing.

I currently use just over 6oz of Power Service and 2oz of 2-cycle oil. Already decided to go 8/8 starting on the next fillup.

Any ideas?