This is a 1988 two stroke Trail Boss.

Hooked up a Trailtech Vapor, and discovered that the ignition fires twice for each revolution.

What is the technical reason that this is done this way

 

Should only be firing once every revolution.

 

2 strokes fire once every revolution, 4 strokes fire once every OTHER revolution.

 

Curious as to how the trail tech is letting you know how often it fires. Had one on my 4 stroke and that wasn't one of it's functions.

 

Can't remember but it seems you can set it for 1 pulse per revolution.

 

We crosschecked with a scope, so we are certain it is firing twice per revolution.

The Vapor has a frequency counter, and is set to "1" by default, with other settings being 2 or 0.5. Set to "2", the freq was reading @900 rpm at idle. I have the idle setting high deliberately, as it would stall on the trail when idling after it gets hot. The manual says idle is 800 (not in front of me now, might be 850)


Internet searching suggests this is something that is done on some 2 strokes, and so it sparks on the exhaust phase, question is why ?

 

Only thing I can think of is to make sure all the fuel burned.

 

That's it. just to ensure full combustion.

 

Can you send that to my wife? She'll never believe I was right.

 

just a result of a non digital ignition. the ignition coil on the stator plate. creates the power for the spark and also controls the timing of the spark. It wastes the other spark a bdc. Just a result of a simple system, not for any useful purpose though. clip-on tach/hourmeters will show double the actual rpm.

A digital iginition like the system used on 94 and up xplorer/sportsman 400. Uses a crank sensor mounted on the outside of the fylwheel. picking up off a flat spot on the flywheel. Sending only one pulse to the cdi box per rev.