'81 Shovelhead, 10:1 compression, stock cam, S&S "E", Power arc single fire ignition w/ VOES installed, 2" drag pipes. When the engine first starts, it seems to only fire on the front cylinder until it starts to warm up. After a few minutes the rear cylinder starts to fire. After the bike has run for awhile, it starts normally. No issues with misfiring, acceleration or power. The ignition is set up for multi-fire. I thought maybe a valve wasn't closing so I adjusted the pushrods. Timing is set properly. Any ideas?
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I am Trying to figure out how it is Single fire ...but set up for "multi fire"..?? BTW...Never gonna run correctly with 2" pipes of any kind...But...I know from experience that falls on deaf ears...I'll just say...Tole Ya....

 

The cylinders fire individually, hence single fire.
On each compression stroke they fire at the appropriate advance timing, again at tdc and again at 5 degrees after tdc. Hence multi fire.

 

There are anti-reversion cones at the flange end of the pipe.