Hi D8Dude, thanks for the response. This is exactly where my thinking is - there are only the 2 options     

Your understanding is correct, the only thing to be aware of is that the D7 and I believe the D8 both utilised an odd and even firing pattern depending on model of machine. I believe the changeover from odd firing to even firing for the D7's was when the D7 17A was introduced, also changing to the updraft carburettor if I'm correct.

D8Dude, Thanks again for your help. I did read on another forum that there was an even firing pony motor at some point but, like you say, this happened much later than my 9G so I had discounted this as a possibility. My parts book shows a crank with crank pins 180 deg apart so i'm pretty sure its an odd firing engine (will double check).  

Isn't an even firing engine's timing 180 degrees apart? I think you have the odd and even mixed up. My 15A D8's are I believe even firing as the crank pins are 180 degrees apart but apparently earlier models has odd firing but I don't know the exact degrees but something like 240 and 120 and that was done to assist in hand starting the engine.

I'm not 100% sure, but what I have read would suggest that the horizontally opposed & vertical pony engines with the crank pins in line are even fire engines. This makes sense (in my head anyway) as they would FIRE, MISS, FIRE, MISS at 90 deg intervals (evenly) whereas the vertical pony engines with the crank pins 180 deg apart would FIRE, FIRE, MISS, MISS at 90 deg intervals (oddly). Happy to be corrected, no problem. Here is the link to where I got the idea talk.newagtalk.com/forums/thread-view.as...e=nested&setCookie=1

Sorry you are correct. I had it in my mind that the journals were 180 degrees apart on the 15A but they are in line which would make it an even firing engine.

You are correct about the 90⁰ intervals for the magneto as it only turns at half the speed of the engine crankshaft so the firing events are in time with the compression strokes of each cylinder. Being a 2 cylinder 4 stroke engine firing events are 180⁰ apart, 540⁰ apart, 180⁰ apart and so on for the odd firing engine, as opposed to 360⁰, 360⁰, 360⁰ for the even firing engine. I could be corrected, but this is my understanding of how each engine operates. I've probably run off track from your original post, but it's good to have an understanding of the difference between the two styles of engine and the consequence it has on spark timing.

No problem running off track, improving understanding is 1/2 the battle!. The original issue will be sorted eventually, I'm sure of it. 

  Hi all, I should have updated this. My mag man figured it out in the end. The plate inside the mag that bolts on with the pan head screws can be installed at 180 degrees from what is shown in the photo, which was causing it to be off - now corrected