Hi Bob
Great minds must run in sync, about grounding out individual cylinders to find the source of a problem. Adding in taking video and sound recording improves on the old test of just grounding out the plugs one at a time.
Did this trying to track down a noise on the engine that went into the C60L video link
http://www.canadianmilitarypattern.c...PANDED%201.wmv.
If you want to hear what my 235 sounds like here is the link
http://www.canadianmilitarypattern.c...l%20videos.wmv all the engine videos are on
http://www.canadianmilitarypattern.c...ineTesting.htm .
People may think I'm nuts for all the photos and videos I shoot of the CMPs (they're probably right) one of my reasons is of course to share but the other is that I use the videos and photos to cogitate over problems.
Question this engine did run smooth at one time after it was rebuild correct? The roughness is something that has developed? If the engine is suddenly unbalanced in its running along with backfiring I would begin to suspect that an intake valve is sticking open. Remember I had this problem with the 261 engine a couple of months after it was rebuilt, in my case the valve finally stuck.
Cheers Phil