Modifying a automotive tach for 2 stroke ii cyl?

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c4mo
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Modifying a automotive tach for 2 stroke 2 cyl?

Im curious if a automotive tach could be modified to be used in a two stroke two cylinder engine? The application is a 96 seadoo with a 717 Rotax engine. The OEM tach hooks to the power stator wires, and information technology reads the RPM from the changing voltage (AC) on the stator. (3 wires. +,-, pulse). The factory tach are not accurate and well-nigh expert tachs sold for this type of engine are pricey. Most aftermarket tachs just claw to the spark plug wire. Example,
http://www.watcon.com/tools/pet-2100-dx
Thanks

Morgan Allen

c4mo
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Re: Modifying a automotive tach for 2 stroke ii cyl?

Mail service by c4mo »

Likewise plant this if helpful;
Seadoo ignition systems are wasted spark systems, meaning both spark plugs burn at the same fourth dimension. Once at tdc, and over again at the bottom of the stroke, when the other cylinder is at tdc. Therefore each plug fires twice per revelution. And then you need to gear up your tach upwardly accordingly.

Morgan Allen

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Re: Modifying a automotive tach for 2 stroke 2 cyl?

Post by lorax »

I don't know jack about SeaDoo ignitions, but my guess is that there is a reason why the manufacturing plant tack uses the power stator and not the ignition. I accept it that the tach is reading the cycle wave of the electric current from the alternator and using it to determine the RPM. The fact that afterwards market tachs utilise the sparkplug tells me that you are not going to be able to use an automotive tach. The fact that it fires both coils together is non a problem. Its still firing them twice per revolution which would make any 4 cylinder machine motive tach work, if yous could trigger the tach. That'south the problem

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Re: Modifying a automotive tach for two stroke 2 cyl?

Post by Truckedup »

Peak Racing ,and others, sell tachs with a selector from ane-12 cylinders 4 stroke and information technology as well includes a spark plug pick up ... They are about 80-120 bucks just are 3-three/8 inch typical sized tachs and require 12 volts. You might need something really water proof? Anyways, I use the $80 Equis version on my race cycle,information technology'south accurate and the needle didn't autumn off.

Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by burn down

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Re: Modifying a automotive tach for 2 stroke 2 cyl?

Post by srq »

Most all outboards, snowmobiles. PWC's and the like use what they call a 12 pole stator for their alternator and for their tach outputs. Merely look for a tach that has an aligning setting spiral on the back for 1-12 cylinders (usually has four-6-8-12) on the dorsum and you lot'll be fine. Put it on position 12. They mostly hook upward to ane of the a/c output wires (on marine engines they can exist identified as the yellow wire with a carmine strip around them - BIA code) of the stator that go to the rectifier. The other to basis. Most any skillful Marine Tach should have these features
I tin supply you with wiring diagrams real piece of cake if yous demand them.
If your auto tach doesn't have a 12 pole setting I am not presently aware of any adapter to catechumen the one-time style four-6-8- cylinder tach.
Good luck
WB