IO-360 A1A What Mag Timing 20 or 25 Deg. BTDC?

[KSMooniac]

My 1991 Factory Overhaul IO-360-A3B6D (also installed BY Lycoming in PA) shows 25 deg BTDC on the data plate.

[aaronk25]

One quick note on this thread is I just had a bunch of work done and the mooney dealer mistakenly set the timing to 20 degrees. When they did this they rebuilt the mags,and installed tempest fine wire plugs and gami injectors. Even after going to gami and having John Paul go up with me and tune them I still was having issues getting a fuel flow below 9.2 at low altitudes when wide open, so in a sense it wouldn't run much more than 40 degrees lean of peak smoothly.

This was with a .1gph gami spread. So that combined with 20 degree cooler head temps and a 3-5kts speed loss got me thinking something's wrong because the tempest fine wire plugs should make it run even smoother than before and allow for leaner oops than massives, but I was unsure as I changed a few things at once....(note to self don't change more than one thing at a time)

Just had a mechanic check the timing L mag at 19 R mag at 20. Damn it. Not gonna say who did it but its a well known shop. I suppose mechanics get used to 20 so I can understand how it happened but darn it, not cool. Ill fly it tomorrow but for what its worth the point of the post is this:

Massive spark plugs with 1000 hours on them that are flat ass worn out and mags that haven't been touched for 700 hours at 25 degrees performe better than overhauled mags set at 20 degrees with bran new tempest fine wire plugs.

Timing makes a hell of a difference.