Thanks dieselgman. We couldn't have done this without your help!
B&D- great article, very comprehensive.
Some thoughts about sparking the DES 8/1 on propane:
After some struggling due to my own inexperience with spark systems, I decided to use the venerable GM L2 system (Delphi GN10119 or UF262T), as it integrates both coil and spark module, which only leaves me with a simple 555 circuit to trigger it with a +5V dwell pulse and we have a powerful, state of the art spark system. I was surprised that with propane, under heavy loads and full temperature, such a hot spark was needed.
Here's a nice write up on the GM L2 coil near plug units and the pinout to drive it:
http://www.megamanual.com/seq/coils.htmWe also switched to a VERY long spark plug, the NGK LFR4A-E. It gets the tip down near the "smiley" mouth of the indirect injection cavity. This seems to help.
Spark timing seems non-critical, around the normal IP injection timing or a little before works well at 810 rpm.
Fixed timing is adequate for starting, no retarding needed.
We had to go to magnet on the flywheel for a more stable spark timing; the hall effect sensor trip point was too variable with the IP cam follower magnet alone. So I use the IP hall effect switch set to turn on early-late to enable the flywheel sensor. A wasted spark system does work fine, also. I'll post a schematic for the spark/dwell circuit when I get it drawn up properly. It is presently still in my own shorthand/hen scratch.