Hey, hold on a minute...

The distributor shouldn't be firing the #1 plug when the intake valve is open. That is the transition between exhaust stroke and intake stroke, when the exhaust valve has just closed and the intake is just starting to open.

It should fire on the next revolution, at the end of the compression stroke when both valves are closed.

What the manual should say is this: When the flywheel ball and bellhousing pointer line up (window in bellhousing right above starter) The #6 intake valve should begin to open. Then set the rotor to point at the #1 sparkplug.

That is because the #1 and #6 pistons reach TDC at the same time. When one is at the end of its compression stroke and ready to fire for the power stroke, the other is at the end of its exhaust stroke and about to suck in more gas thru intake valve for the intake stroke.

If the engine throws a huge backfire, you've got the plug wires out of order for sure.

Whats that old saying for the firing order:
1-5-3-6-2-4

15 is too young
36 is too old
24 is just right

hope this helps

chiphead

Preaching the Hot Rod Gospel according to the 4-stroke apostles:

Suck, Squish, Fire and Fumes