Well Mister Buccaneer here is my two cents on this question. Back when I was racing snowmobiles we ran the points a little wide. Wider points make more advance. Narrower points retard timing. Those old motors didn’t care much. Can you put a dial indicator in the spark plug hole and check where the points break? Your new coil might be sparking at a different spot than the original one. At start up you need about .020 thou BTDC to get you going. A dial indicator and a continuity light should tell you where the points break.
dale
Advance / Retard on outboard magnetos is determined by where you
move the mag plate, hence I can make the points open “sooner” or “later”
by moving the plate.
I can’t remember if the old snowmobiles had any kind of mechanical
advance, but the few times I did mess with them, from what I remember,
the specs were for the points to open a certain “piston travel” BTDC.
I can certainly try setting the point’s to .018 before I designate this
little Merc to “Saw horse Queen” status.
I messed around with any potential “crankcase” pressure losses,
checking bolts as “tight”, and had the poppet valve carb off twice,
the last time lapping the carb flange that mates to the crankcase.
I lapped the mating flange on the crankcase when I had it all apart.
I also messed around with different spark plugs.
I did get it running a little longer, but it just won’t take the leap
of faith to stay running.
I checked the compression, and it’s 87 psi. I had lightly hone the cylinder
and unstuck and decarboned the ring grooves.
Out of desperation and curiosity, I checked the compression on
the little Merc K3-1A I was just given, and it’s 88 psi.
Unless they’re both “worn out”, one would think that’s enough!
Video of today’s progress. I made improvements in length of run,
opening the needle valve slowly, up to about one turn open,
but from there, it was “down hill”.
Any ideas?
https://youtu.be/MF-LqCNsGj8
Prepare to be boarded!