88 454 Merc Momentary Loss of RPM *paging Charlie*

Do you have a kill switch? Often the lanyard side will weaken and allow the switch to momentarily activate.
 
Out this weekend and same result. I am going to swap the coil from the port engine and see if I can replicate.
 
When you said it only happens when hot, I was going to suggest the coil swap. If and when you replace a TB coil, you have to get the right one. No internal resistor. All the resistor does is reduce the voltage to the points so they don't melt...and since the TB ignition doesn't have points...
 
Charlie, why would the heat affect the Coil? When you say that TB ignition runs directly off the Battery is there a seperate feed? Because....I did replace the house bank earlier in the season, there was a wire running to the positive terminal. The end point ring was worn and broke, I assumed that it was the bilge pump and just trapped the wire. Since the bilge has been working I have not thought about it...If that is in fact the ignition wire it may be losing contact.
 
Not sure what the solid state coils do but the older 'can' type coils were filled with oil to control heat. One of the things that happen when there's resistance in a circuit is that it builds heat. Heat creates resistance and resistance creates more heat. In a can type coil there are hundreds of wrappings of wires in the primary coil and it's confined in the can. It gets hot and the hotter it gets the more it affects the thin gauge wires that eventually break down.

When I say the TB coil runs straight off the 12v battery (what the book says) it still has to go thru the ignition switch. Not sure what that wire goes to but you should track it down. Knowing what gauge and color wire also helps it's purpose.
 
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