Set cranking advance to -5.

Change your timing map so that in the sub 700rpm/80+ kPa region, your timing is also around -5 (must be less than 0 degrees - the more negative it is, the less likely it is to cause a kickback). Something like this:



Test and report back on success or failure, also post what your crank decoding circuit is (optoisolator, V3.0 VR circuit with pots, MAX9926) or if you don't know that, which ECU you have.

 

Will try this and report back, although my starter kick back was 95% fixed by replacing the starter. New starter spins significantly faster and almost never kicks back unlike the old one.

 

Seems to have cured kickback that I’ve had for years. Running an MS3 basic.

 

Good to know! This applies to any ECU, not just Basic MS3s. It should also work on MS2s and any flavor MS3, as long as you are using the stock crank trigger wheel and not the 36-2.

 

Nice, thanks for sharing. I've always had good luck with -2 degrees cranking and on the table, but never tried going much farther than that. How do 36-2 wheel applications differ in this regard?

 

The problem comes from the low tooth count and from the position that the 4 teeth on the crank are placed. Firing at 0* or less during startup, ensures that the ECU has just seen one of the 4 teeth, so the timing will be accurate. With the spacing of the OEM trigger wheel (70*-110*-70*-110*), the ECU has to predict from a tooth that was seen 70* or 110* ago, when to fire. Since the engine doesn't have a constant rotational speed during cranking, there is a very large error potential when calculating when to fire the coils. The 36-2 has one tooth every 10*, so there's zero chance of not firing correctly, as the rotational speed of the engine will be "almost even" in those 10 degrees.

 

Rev,

I'm hopeful you and yours are well.

What's the difference between doing what you outlined above, and changing the Cranking Advance to a similar number in the Ignition Options/Wheel Decoder pulldown?

Thanks,

 

If you read my first post, the first line says to set the cranking advance to -5 and then to apply the -5 to the map. So you need to do both, not just the one.

 

I read the thread, including your first post.

Your explanation of what is going on makes perfect sense. What I want to know is why just modifying Cranking Advance in the Ignition Options pull down isn't good enough. If the MS uses the Cranking Advance setting for the cranking advance, why do I want to use something other than a setting for a running engine in the other ignition boxes?

I made the changes you suggested (even though I don't have any starter kickback), and my motor would start easier in the cold (mid-20s temps), but the rpms would drop over a few seconds and then the engine would die. She didn't do that before I made your changes.,

 

The kickback can still occur just above your cranking RPM, so a very fast transition from -5 to 8/10 degrees can induce the kickback at say, 400rpm, as the rotational speed is still low and uneven.

 

Thanks. Have a cat...

 

Is this something that could be fixed with instead increasing the "skip cycles on cranking" setting? or is that meant to fix a different issue? I applied the changes and it seems to have fixed my starter kickback at -1 or -2 degrees, but then poking around I also saw that my "skip cycles while cranking" was set to 0

 

No.

 

So, for the folks that like to visualize things.

Here is what is going on during cranking.

I have set the cranking advance to 10* (so 10* before TDC).

Notice how the pink crank pulse and the green ignition pulse almost overlap.


10* (10* BTDC) ignition timing at 200rpm.

Now, let's zoom in and analyze a bit.




What you can see, is that the spark doesn't overlap. It comes barely just before the crank pulse. This is BAD, as this means the calculation for the spark have been made from the previous tooth, which is almost 70* before. And due to the engine firing unevenly at this point, you can't predict when to send the spark when there is such a huge delay. The spark will definitely arrive at an incorrect point. Fore the timing to be accurate at this point, the spark needs to come shorty after the crank pulse's falling edge.

Now, let's see what happens when you set the cranking advance to -5* (ie, 5* after TDC).



Now, the spark is set to -5, and we can clearly see that the spark generation begins very shortly after the crank pulse's falling edge. This results in a very accurate spark, and no kickback.

Things to note: You can get a few extra degrees if you switch to rising edge. If your ECU uses the MAX9926, your timing may have small errors overall if you use rising edge. If you use the optocoupler circuit, you will be ok but you need to verify your timing again with a timing light.

With rising edge, you can use about 1* cranking advance (aka 1* BTDC).

Do note that the test was done on the bench with 14V. As you crank a real, cold engine, the battery voltage drops, the dwell time increases, so the ignition pulse has to start earlier. This also explains why this problem is worse on a cold engine.