How do you check the ignition timing?
 

Which wire do you remove from the distributer to check the base timing? Thanks

What year engine? What ignition system? If it's a thunderbolt IV or V, look for a purple wire with white stripe coming from the dist. that should have a female connector with a rubber plug in it- plug comes out and you ground that wire. If it's EFI, you jump pins A and B together on the data port connector.

Thunderbolt IV
 

It is a thunderbolt IV. It has a white wire with red strip and a white wire with a green strip on the back of the distributor. Where is the purple? My boat is not EFI. Carb and normal easy to work on.Thanks

I beleive on that ignition sys. you don't remove any wires, just hook up the light, are you after initial timing or max timing, the ignition module should say what degree of advance it applies.