Using Negative side of coil for pickup

[banzairx7]

Im doing a fuel only Microsquirt on a single cylinder motorcycle. I've got everything wired up in the way that I think is correct but I don't see any rpm signal when cranking. So obviously my interpretation of how to do it is wrong. I see two ways I messed up. First is I took the optoin- put a 4.7Kohm resistor from it to the 12v switch power for the microsquirt per a post i found on here. Second was where I hooked to for the coil negative. It wasn't real obvious to me what was the negative side. The coil only has one spade terminal. The other wire that goes to it is hooked to the bolt that goes through one leg of the coil that bolts it down. Thats what I hooked optoin+ to. Maybe the spade terminal was negative? Anything else I should be looking for?

[Matt Cramer]

Is this a CDI ignition? If so, it may not be possible to use the coil as a trigger, particularly since CDI ignitions often run at ~400 volts instead of 12.

[banzairx7]

Yes it is a CDI ignition. I may have to use the input signal to the CDI? Not what I wanted to hear. Ive read through using the flywheel triggers and it comes across as VERY difficult. With out an oscilliscope(to see what the flywheel trigger outputs) I have no idea how to setup the microsquirt.

[Matt Cramer]

How many wires are on the flywheel trigger's sensor?

[banzairx7]

It has two wires. Shop manual says it has a resistance of 280-420 ohms @ 68 degrees. The I guess what you'd call trigger tooth on the flywheel is strip of metal ~2" long x 1/4" wide x 1/8" high on a 6" diameter flywheel.

There is also a much larger three wire coil that the shop manual calls a source coil. Im not sure what its purpose is.

[Matt Cramer]

Sounds like it's a VR sensor - I suspect you could split its output between your CDI box and the Microsquirt's VR input.

[banzairx7]

OK progress has been made! I spliced into the two wires from the VR sensor. I now have a tach signal. Im still not there yet though. When cranking the tach is reading very high. I see it jump to 18,000rpm then seems to settle into the 7,000-9,000rpm range. I'm not sure what the real rpm is at cranking but my guess is its one tenth of what I'm getting. What could be causing this?

The engine is a Yamaha 170cc(125cc with a big bore kit) two stroke. I've got megatune set for single cylinder, two stroke, fuel only, rising edge trigger. Setting the trigger to falling made no difference.

Thank you for all your help so far. I'd been stranded with out it.