1987 Mercury 2-stroke won't start

[mmac]

Bought this used. Ran but not great. Rebuilt carb. Fuel pump on side of carb. Won't start. Occasional backfire out exhaust. Good compression. Spark at plugs. New stater and trigger. This model has primer and it does spray fuel. I suspect a timing issue however it is a pull start. Not sure where to start on timing concern.