One possibility is your starting fuel.
Probably your start fuel is too rich or too lean. Open the throttle as you crank it. If it catches then your start fuel is too rich. If it doesn't then it is probably too lean. I have found that on strokers or motors with large injectors the start fuel needs to trimmed to get them to start.
A PMS or similar device that allows for quick changes is great for this type problem.
Of course if the base timing is way out it still won't fire. Good luck.
Mike
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