SO I’ve found the issue. The woodruff key aligning the flywheel has sheared off and put it out of place and hence timing. I’ve replaced the key and it started and ran. But it’s done the same thing again. Would there be a particular reason why it’s sheared off?Quite a few potential variables there. I pretty much covered em in post #1307. The 1201 is one of two flywheels used on the points 051's. It's safe to say you have a timing issue given the backfire. Aside from checking the condition and gap of the points, magneto air gap, and possibly trying a new condenser, may want to make sure the crank is actually compatible with the ignition.