BTW, after reading a lot of info on vapor lock issues, and talking to the folks out here, I decided to start with the cheap stuff first…  then work my way up.

I was able to duplicate the problem this Sunday.  I flew up to Atlantic again to go to church with Suzanne.  Two shots of prime when dead cold, no start.  Two more shots of prime, and it caught.  Normal mag drop, except the left mag (impulse coupled) was 150rpm, as compared to the right which was (and has always been) a solid 100rpm.  They used to both be 100rpm.  Cruise at 5,500ft, leaned out, enroute descent into Atlantic.  UBG-16 showed the CHTs dropped off the bottom of the scale, and the EGT dropped down to about 1100.  Parked the plane.

Two hours later, I went to re-start.  Cylinders were cool to the touch, and the oil on the dipstick was still warm.  Fuel pressure still showed about 3psi, about a pound lower than when I shut it down.  First attempt, no prime, mixture full rich, throttle cracked a half inch.  No start.  Added two shots of prime, and tried again.  No start.  Added two more shots of prime, and “pumped” the throttle while cranking.  Got a few feeble attempts at start, but it wouldn’t run.  Final attempt, mixture at cutoff, no prime, throttle cracked a half inch.  It caught, and I immediately stabbed in the mixture to keep it running.  Normal flight back home, at altitudes between 2,000 and 4,000feet, full throttle, full rich.  OAT was about 80 degrees.  I noticed I was about 5mph slower than normal, until I leaned out the mixture a bit, and I was able to pick up the speed again.

After landing back home, I let it sit out in the sun for a half hour while I busied myself in the hangar, a circumstance similar to what happened on Memorial Day.  Nothing I could do would get it to start again.

Talked to my mechanic, and he suggested I remove the left (impulse coupled) mag and take it in to have it looked at.  According to my records, in May of 2012 I was having problems with both mags, and we pulled them both.  The left we put new points and rotor into, but no matter what we did we couldn’t get the right one to behave normally…  wound up buying a new right mag.  Both are Slick mags.  Left mag has 185 hours since the points and rotor, and the right mag has 170 hours on it.  I spoke to the guy who runs our Aero Club on base, and he says it’s behaving like some of his aircraft do when the impulse coupled mag starts to go…  weak spark, harder and harder “hot” starts.  He agreed that checking out the left mag (which is very old, by the way) is probably a good idea.

Plugs all look good, all the gaps are within spec.

Of course, if this doesn’t work, then I’m going to get a Slick Start…  I know several people who have them, and they love them.  The Aero Club finally had to put one on their fuel injected Piper Arrow, which patently refused to start if it had been run at all during the day, even after they had replaced both magnetos….  Cured the problem.

Frank