Timing a MkIII with Crank Notch

I put a Tri Spark on my 75 and in doing so, I was thinking that no matter how accurately I strobe the mark, if the indicator scale was off I wouldn't really know where the timing was set. I assumed that a machined notch in the crank is more precise than a bolted on sheet metal scale, so I checked them against each other.
Pictures show the notch centered at 28 deg, and the indicator scale on 29 deg. Not bad really, but it just shows that your advance may not always be what you think it is.
I wonder how much variation there is among the 75 bikes?
I just strobed my timing to be at 27 deg and it seems to be fine. I love the Tri Spark.
Also note that I put a red colored dot above the timing mark to eliminate confusion with the 180 out mark.





JD75

jaydee75 said:

I put a Tri Spark on my 75 and in doing so, I was thinking that no matter how accurately I strobe the mark, if the indicator scale was off I wouldn't really know where the timing was set. I assumed that a machined notch in the crank is more precise than a bolted on sheet metal scale, so I checked them against each other.
Pictures show the notch centered at 28 deg, and the indicator scale on 29 deg. Not bad really, but it just shows that your advance may not always be what you think it is.

Click to expand...

The only way to know for certain is to check it with a timing disc.

I did the same thing on my '75 and got the same results as you.