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I have a mini Tach/Hour meter that you attached to one of the spark plug wires to get a reading. I use this for maintenance only then take it off when not using it. When I had my V-Star 650 and hooked it up to the rear cylinder as instructed it gave me the true RPM's the bike is running at. When I hook it up to my 900LT it is giving me only 1/2. We had a post last week where someone was asking what RPM's we were running at certain speeds. I decided to try it out and found that I could not get the bike to go over 1900 RPM and that I was idling at 480 rpm's. THat's when I realized that something was wrong.

Is there something different about our bike's??
 

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you need an adapter of some sort for tachs. they read at a half value. im not mechanically inclined enough to explain the phenomenon but it has to do with the way the plugs are fired.
 

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Maybe I am just simplistic, but if it reads at haf value, couldn't I just double the reading as long as it is a test tech anyway. I understand wanting a mounted unit to read correctly. But for test purposes, I would think you could just do a little math. Also, I am interested in getting a test tach as described. Can someone give some advise on where to find one and what I need to look for? Thanks in advance.
 

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The reason it reads at half value is because the VN900 doesn't use a wasted spark ignition system. I suspect it has a cam position sensor, or something to that effect so it knows only to fire on the compression stroke. A wasted spark ignition would fire on the exhaust stroke as well. So the bike fires half as often as most tachs would expect.

There are tachs you can buy that are rigged for that out of the box, no?
 
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