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jefffoxsr said:
Once every revolution, twice every revolution, or once every 2 revolutions?

I need to know this to buy the correct kind of tachometer.

http://www.tinytach.com/tinytach/gasoline.php
4-stroke is every other rev to TDC. 2-stroke is every rev.

Both are firing at just a few degrees before TDC.

Rappy is a 4-stroke.

Intake(down) - sucks in air/fuel mix
Compression (up) - squeezes air/fuel mix
Power (down) - exploding air/fuel mix
Exhaust (up) - pushes waste gases out
Repeat
 

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Discussion Starter · #3 ·
The reason I asked is because I have the standard tiny tach for 4 strokes. It has worked accurately on every other quad and motorcyle, etc. that I have owned. I hooked it up to the raptor today and it read 1/2 of the rpm. Idle read 820 RPM.
I checked the tach again on other machines I own and the rpm was correct on those machines.
The standard tach is used on engines that fire once per stroke.

So that leads me to believe that the 700 fires once every 2 revolutions.

Can anyone verify this.
 

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This ignition could be a waste spark type that fires every revolution. Alot of autos use this style.
 

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Ya..the guy who posted the second post of the thread can...and did...verify it.

jefffoxsr said:
The reason I asked is because I have the standard tiny tach for 4 strokes. It has worked accurately on every other quad and motorcyle, etc. that I have owned. I hooked it up to the raptor today and it read 1/2 of the rpm. Idle read 820 RPM.
I checked the tach again on other machines I own and the rpm was correct on those machines.
The standard tach is used on engines that fire once per stroke.

So that leads me to believe that the 700 fires once every 2 revolutions.

Can anyone verify this.
 

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Discussion Starter · #6 ·
Ok,
I wonder why all my other 4 stroke machines read correctly on this standard "tiny tach", and the raptor reads 1/2 the rpm that it should.

I'm out of ideas as to why this would happen, does anyone have any?

It may have something to do with the engine using EFI and a crank sensor.
 

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I just wired a tack up this week. (actually one for a car) and had it set to 4 cyl and it was reading 1/4 of what it should have been. If the tack you are using is for "other 4 strokes" are they single or twin cylinder? I would bet twin. I think it fires every other stroke otherwise I would have read 1/2 of what the rpms really were. I could be wrong here but that is what I concluded.
Anyone know where you can get a dial type tach for a a single cyl 4 stroke?????? I am just not into digital or bargraphs like the vapor.
Let me know if you come up with anything.
 

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It fires every time the trigger on the flywheel passes the magnetic pickup in the crank case. Any engine needs a cam trigger to mark a cylinder to start a sequence.. The crank turns 2 times per engine cycle so it sparks on compression stroke and exhaust stroke, also called wasted spark. BTW wasted spark ignites the unburnt fuel in the exhaust and thus makes more power.
 
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