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My bike (1980 kz650) dident come with a speedo or a tach, I bought a cheap used mini speedo off ebay and because im crazy and need thing symetrical I need to get a tach on there as well.

I found a matching (appearence wise) tach but after hours of searching the web I cant find what drive I need (it was 1:5). I found some threads on a few forums that made it sound like any bike can be made to accept an electric tach.

Question:
what drive ratio does a kz650 I need -or- how would I go about switching from mechanical to electronic?
 

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Don't know about drive ratios. If you're converting to electronic it won't matter anyway...

FR
 

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after a lengthy conversation with autometer reguarding cb750s and electronic tachs, this is what I have found out:

there are basically two types of ignition systems - single pulse and dual pulse (wasted spark). A single pulse does exactly how it sounds, fires the coils only when the piston is on the compression stroke. A dual pulse fires the piston when on the compression stroke and on the exhaust stroke (usually this is because one coil fires 2 cylinders and when one piston is on its compression stroke the other on its exhaust stroke). From there you have to find a tach that is setup for either single pulse, or dual pulse, plus the number of cylinders of your bike. Once you know that you simply wire the tach to the coil that fires the #1 piston and off you go. Autometer makes tachs for drag bike so they have a decent selection that will work, but they are not cheap. There are other electrical tachs out there, but you are on your own to research that.

mini cable tachs and old factory tachs are usually not 100% accurate and are more like advisories than anything else. They are also not always accurate when new, as anyone who bought a new R6 last year will tell you (and that was electric).
 

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This one came from Summit for around $30. It's got an 11K RPM limit and is about 2" in diameter. I've got the same "wasted spark" ignition as a CB750 and wired it into one of the two coils (I don't remember if it's 1-4 or 2-3 or if it mattered). It weighs a pound or two less than the mechanical tach and works well in the garage. It's not on permanently yet as I'm re-working the top clamp to mount it. It compliments my $10 bike speedo for poor man's data acquisition.

 

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That's a nice solution. These old mechanical tachs aren't the greatest. And that's a great price. And no power robbing parasitic drag off the camshaft! I'll bet you that'll gain you an extra RPM.


FR
 
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