470 Mercruiser Voltage issue or fuel?

I have a 3.7 merc 1984 with the stator charging system.
After about 30 min at mid throttle yesterday motor started to run rough. Loss of power. If I hit my trim adjustmet the motor would back fire.
I could trottle down to lower RPM and cruise but with any load backfire.
When putting the motor in Neutral I could rev engine with no problems. No power and rough rpm only under load.
I noticed voltage meter reading around 10 to 11 volts and wondered if low voltage could be the problem and when I hit the trim it pulled volts away from the ignition system(point and dist set up). And caused problem?
Other option was the carb adjust as it seemed to be running rich.
I shut off battery selector switch and let everything cool down. When I switched the battery back on I noticed my bildge pump instantly kicked on. (found float switch had stuck).Must have been running easily 30 to 40 min while under way.
Could voltage draw be enough to cause ignition mis firing?
.My other thought was as Carb as was running a little rich it may have caused a problem with excess fuel?

I disconnected bildge switch and reset my carb screw to 1-1/2 turns from closed.Was set at approx 2 turns out.

Started boat and saw voltage gauge back up to around 13 volts. Still not what I think it should be.
Was able to run the boat back to the launch 30 min at around 2000 RPM with a load with no symtoms of a problem.
Sorry for the long post, just curious on next course of action. I have an alternator set up that I aquired off of a 140 Mercrusier that I think I may look to install on mine.

Thanks

Re: 470 Mercruiser Voltage issue or fuel?

If your not chargeing the battery and it runs down to 11 volts that will deffiently cause running problems

A real volt meter is the best way to see what the output of the system is as the guage is just a general guide


There are many bracket kits on ebay to bolt on a standard alt

Tommays

Re: 470 Mercruiser Voltage issue or fuel?


Thanks I suspected the voltage drop to be the main issue. It was very noticable in where the gauge position was when I had the problem to where it was once I shut down the bildge pump. System was dfinitely putting out a charge as you rev rpm's. My guess was pump took more over time than what charge could replace and eventually drew battery down.


What are the chances that the alternator off the 140 that I picked up would be sufficient? Also do I need to disconnect the stator set up or disable once the alt is attached?