new symptoms of rpm loss

[DGIFF396]

I have posted about my 78 merc 470 "losing power & bogging down" under load only and only after running for a hour or so straight. If I let it cool or go back to the river the next day it runs fine for another hour or so...did the vacuum test on the fuel and it was fine now Ive come to realize it only seems to do this after about a half hour of pulling a tuber also. It just doesnt want to climb over 3 grand after it starts to act up. As soon as I reach 3000 rpm's it boggs down like a power loss, any ideas? by the way temp never exceeds 155 or so

 

[Don S]

Re: new symptoms of rpm loss

Did the vacuum go up any when it started bogging?

 

[Cuyose]

Re: new symptoms of rpm loss

I have a friends mercruiser that does this as well. Exactly the same symptoms. Since I don't own the boat, I can't troubleshoot much. I did confirm no water in fuel, tank venting fine, and fuel delivery fine as well as flame arrestor not blocking.

I did hear that this could be a symptom of a coil starting to go out. She still had points on her engine and prolly an original coil. One of the plugs was not firing as well. All indicating a need for a overhaul of the ignition system.

Don, could the coil be causing this as residual heat from the engine heats it up after running for a while?