MicroSquirt.com read only forum (Jan.15,2018)

Hello:

Has anybody been able to set up the Dual Spark portion of the Microsquirt controller for a Harley model year 2000 or newer?

I've read the Dual Spark section of the Microsquirt manual several times and the 2.C example is the closet example of what I have. I do know that the Harley has a 32-2 tooth crank wheel and a cam sensor for phasing.

Unfortunately, I don't know what the correct number of teeth settings would be for Skipped Teeth and Delay Teeth because I don’t know the physical relationship between TDC of cylinder one (is that the cylinder closest to the front wheel?), cam sensor, and the two missing teeth on the crank.

Also, how would I check the timing with a timing light to set trigger offset? With the motorcycle set up originally as a fuel injection model there aren’t any timing marks to reference.

Any help will be greatly appreciated.

Sincerely,

Mike Stiffler

Skip teeth depends on no. cylinders, 2 or 4 stroke and whether sequential or wasted. It defines how often you want to spark/ inject. Since you have a cam sensor, you are in sequential mode. If you have 4 cylinders, then you want each cylinder to fire once per 720 crank deg or every 180 deg you want a cylinder to fire. This is half a revolution of the crank wheel or skip_teeth = 16.

As far as the timing between cam, crank it is only necessary for the cam signal to come in sometime before the missing tooth on the compression stroke of cylinder 1. However, you must determine the timing between TDC #1 compression and the missing tooth. This is called degreeing the engine. If nothing else you can hold your finger over the spark hole of #1 and feel the pressure on the compression stroke and see or feel the piston coming up. But this is very crude and I would degree it properly so I could use a timing light.

Hello:

I've attached a 32-2 timing chart for the Harley and wanted to review my Microsquirt settings:

Trigger Wheel Teeth (M) is 32
Missing Teeth (N) is 2
Skip Teeth is 32
Delay Teeth based on chart is 9
Dual Output trigger offset is -45 degrees (315 minus 360)

Based on the attached timing chart do you agree with the Delay Teeth of 9?

Do you agree that the trigger offset of negative 45 degrees is correct?

Thank you,

Mike Stiffler

The teeth are correct and I assume you set the Dual Spark Option to Rising or Falling edge cam synch and the cam synch comes in during or before the 1st missing tooth gap in the figure. If you choose Delay = 9 teeth, you are saying that your tach cycles will start there, and that is TDC no.1 comp, so your trigger offset is 0 deg - that is the tach cycle begins at 9 teeth past missing and that is where TDC occurs. So Delay = 9T and trig offset = 0 is a valid combo. At that point the code will set up to fire 2 tach cycles (2x32 teeth) down, which would again bring you to no. 1 TDC.

In setting this up you have to assume cylinder 2 is even fire so make a copy and mark where cylinder 2 TDC comp would be if it were an even fire engine. From your diagram it would coincide with cyl 1 TDC EXH. But if you add 4 teeth worth of advance (45 in degrees) that will give you the same actual advance as cylinder 1 gets. So you need to set the #2 output offset to +45 deg, plus angles always being advance/ BTDC.

Why are you recommending a positive number for Dual Spark trigger offset when the manual highly recommends negative numbers?

"But for Dual Spark, because it is too complicated and there is not enough RAM or CPU time, you must start and finish both dwell and spark within the time between 2 consecutive tach pulses. In this case we always want to use the negative y degrees, or else the math ends up coming out incorrect in the code."

I am not recommending a pos trigger offset. The only positive number is the +45 deg ign2 offset, which is not a trigger offset - it is simply an advance (therefore positive) that gets added only to ign3 output .

I'm lost, what's the manual refering to that should be a negative number and what is ign 3 for a two cylinder engine? Do you have any additional reference material that could help me understand? Maybe a previous thread as reference? I'm I using the wrong terms? Any help would be greatly appreciated.

There are threads all over on dual spark configurations. For 0 delay teeth, trigger offset is the difference in crank degrees between when the crank sensor detects the first tooth after the missing tooth and when TDC occurred for the no. 1 cylinder. If the sensor detected the tooth x deg after TDC, then trigger offset is -x deg. Now in most cases, the no. 1 cyl TDC occurs before the first tooth after the missing teeth. To meet the requirement that it be ATDC, you can do one of 3 things: move the sensor, take no. 2 cylinder as the first cylinder and wire it to ign1, or introduce delay teeth. The latter is the easiest, but when you do this, then trigger offset becomes referenced to the delay tooth. If delay = 0, it is the 1st tooth after missing, if delay = 1, it is the 2nd tooth after the missing one, etc, and each time you go past a tooth you subtract the equivalent of 1 tooth in degrees from the trigger offset for 0 delay teeth until it becomes 0 or negative. So this trigger offset is now the difference in crank deg between no.1 cyl TDC and when the sensor detects the delay tooth.

If there was any reference to ign3 in the manual it is either a typo or cyl 3 was meant. There is no ign3 output in microsquirt.

I know this is difficult to understand. On our plate is the writing of a program that will display a wheel and let you place the crank and cam sensors where you want them and the program will figure out the settings for you. However, there are, even for 1 and 2 cylinders, a lot of options - you have 2 and 4 stroke, wasted/ sequential, even/ odd fire, and each possibility for no. cylinders has its own quirks. It's not an easy thing to do and will take time.