The timing problem is no problem at all. All references to timing are&n= bsp;in crankshaft degrees and the crankshaft is turning three times fa= ster than the rotor. So start thinking in terms of 1/3 of whatever timi= ng is recommended for a rotary. Then compare that to your automotive experie= nce. The engine will start and run just fine on nearly any timing number you= can think of. For emissions control the rotary has come with timing like 5=20= BTDC and a split of 8 ATDC. A very modest 20 BTDC both is what was used for=20= years in racing and off road and good up to 9,000 RPM. The lower the fuel oc= tane the better the engine runs.

For using avgas with slightly lower flame front speeds a bit more timin= g should be dialed in for good milage.

For constant RPM operation 24 -28 degrees would work well. Even then th= e timing at the rotor face is a very mild 8 degrees BTDC.

The secondary (high voltage) ignition breakdown was for more typical of= points ignitions in the past. Points open slowly and with much electrical n= oise. Each cycle is different from the last. Slow switching a Kettering syst= em allows slow voltage build up on the plug. So a number of viable paths may= charge up before the primary collapse is complete. This flow is subtra= cted from the maximum secondary voltage expected at the plug gap. Later, ele= ctronic switching of Kettering systems eliminates this problem.

So we are left with the "SAG" being caused by plug fouling providing du= al paths for secondary flow, the lead fowling or the electrode gap. Voltage=20= demand at the gap goes up with cylinder pressure. High cylinder pressure occ= urs at full throttle. So, if a slight throttle reduction (lowers cylinder pr= essure) eliminates the problem, it is likely that fouling is the culprit. If= caught away from support, a reduction in plug gap will perk things up for a= while. In the race car I use two MSD 6ALs with rev limiter chips for 9,800=20= RPM and NGK R6725-115 gapped at .010". Too cold a range for aircraft use and= very expensive, but the gap is about right for very high RPM use.

Lynn E. Hanover

In a message dated 4/28/2008 5:07:59 AM Pacific Daylight Time, eanderso= n@carolina.rr.com writes:

You are correct, George. SAG is not real= ly a problem with the ignition
system itself.

SAG (Sparkplug Atte= ntion Getter) appears to be a result of spark plug
fouling. I fly=20= using 100LL and get 20-30 hours on a set of stock plugs
before SAG start= s to occur. It generally starts out infrequently and for
short dur= ation. The symptoms include:

1. First notice is a change=20= in engine tone
2. EGT on the affected rotor will generally decrease= approx 250-300F
3. RPM will drop approx 200-300