28' or 30' timing for a 850 with a Tri-Spark? (2015)

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Trispark max advance is pretty much same as OEM points/AAU so no need to strobe higher. All in by 3k will give you the best performance from a stock engine. FWIW, points/AAU are not limited in any way by their construction as far as setting advance. You can change the springs to adjust where the advance starts and also mod the weights and the weight-stop to adjust maximum distributer advance to wherever you want it.

If you use an E-Ignition that doesn't produce max advance until 5k, you are giving away performance below that RPM.

As noted, it seems logical to assume that advance should continue to increase as RPM goes up but that's not the case because other factors take over in the fuel burn/combustion cycle. As noted, many high-spinning engines prefer some retard at 8k RPM which, of course, can't be done with points/AAU but can with an E-ignition calibrated for the specific engine.

As far as actual advance - I use 34 degrees on my stock 850 Commando for best performance but that's due to the altitude it operates at, 6500 feet and above. When I was in New York at sea level, 31 worked quite well.
 
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