On Sep 25, 6:53 am, wrote:
Hey all. Been meaning to post this for awhile (almost done with the annual now), but campus news
server has been down. Anyway...


The dry tappet clearance might be part of the problem.
The clearances can increase as the cylinder lengthens with heat, and a
few valves might not be opening all the way. But it should be a
consistent lack, not 1 out of 25 takeoffs.
I would suspect that carb icing might be your problem.
It's way more common than many folks think. What are the atmospheric
conditions when this happens? Look for small temperature/dewpoint
spreads. It doesn't have to be cold outside; ice can appear at temps
up to 100°F. Lycomings are ice-resistant because their carbs are
mounted on the oil sump, but if the oil isn't really hot yet, or if
the temps are cooler and the dewpoint isn't far away, ice will form.
Sometimes even if the oil's hot, and even in the full-throttle climb.
Does the engine stumble once in a while in the climb? Probably ice. We
see ice all the time here, even in a dry climate and on Lycomings and
on warm days. Got to know what to watch for.
Check the carb heat immediately before takeoff, at around
12 or 1400 RPM. Should get a drop that stays dropped; any rise after
that with carb heat on, or excessive roughness before it rises,
indicates ice. There have been accidents where engines didn't generate
enough power to sustain a climb, and the cause was pegged as ice that
formed during the taxi, after the runup.

Dan