Hi all. Could someone explain to me please why the timing specs in the mc28 service manual states two BTDC figures for the same RPM?
Does one cylinder fire 10 degrees different to the other, hence the prefered flywheel fitment being from a '21 where the spec is just the one BTDC figure, or am I not reading it properly?

Thanks.
Eggsy.

From PGM-II and onward, separate ignition timing maps for each cylinder were possible.
For PGM-II,... between 1000 and 1800 rpm the rear cylinder timing is retarded compared to the front cylinder to give a smoother idle (when the throttle position is less than 5%)
I will guess that this remained the case for later versions of PGM, but am not sure. I have no experience with the MC28.
This should be easy enough to check with a timing/strobe light.

I am not sure if any of Honda's PGM's do this, but,... I have seen examples where, due to the crankshaft twisting very slightly when under load, one cylinder is slightly advanced compared to the other at certain rev/throttle combinations.
_________________
[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...

Thanks, thats a nice answer, but not really one that answers my query. Slight differences in each cylinders timing are possible obviously for various reasons, but 10 degrees? Seems a bit much to me.

Sure, apart from the special idle condition it would seem pretty odd to have 10º difference in ignition timing between the two cylinders.
Anything over 3º would have me scratching my head.
Fitting the MC21 flywheel (to the MC28) advances the spark by approx 1.0 to 1.5º according to Matt@Tyga in this post.

As I say, I have no experience with the MC28, so that's about as much help as I can give.
Hopefully there will be others that can answer your question properly.
_________________
[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...