TOPIC: HELP Merc 1500 inline Overcharging??

Hi all,
I'm stumped but, have an idea. I have been confounded where my 74 Inline 1500 runs like a top, and tachs out very nicely to 6000 RPM BUT after a few high speed runs it stutters and misfires. It is not mechanical or fuel it is ignition related.
It is not dist wires/cap/plugs.
I had some parts motors so swapped out parts. It has come down to I think I maybe overcharging the battery and be damaging the switchbox during the high RPM runs where voltage output from the stator would be max.
I don't have a voltage gauge in the boat but ran leads to my hand held and voltage is higher than recomended at 4500 rpm(16+volts) and higher than expected (less than 15 volts).
I do have a "marine" battery (not an Optima) in the boat but, I am finding based on battery construction battery may not "regulate" the voltage correctly. I have no accesories on the boat to put a load on the system while running to pull the voltage down.
Has anyone had these issues? What about swapping in a regulator/ rectifier? Ideas on which one? How is it wired in?
I generally have run points Mercs and am guessing that I don't see this issue as there is no switchbox so over voltage would not show this issue.
Help!
Randy

rectifyers dont regulate the volts and at high RPM's they will build up to 18v i have seen if you run a long time. insrall some lights or some thing to use the excess and keep t down with your high speed runs.

I'll reply to my own post with the answer.
Turns out that you must use a standard old battery with the vented caps as that means it is not a low or maintenance free battery.
These batteries self limit the voltage during charging ie., they self regulate. They start to Hydrolize when voltage increases and this effectively puts a load on the charging circuit, pulling charging voltage down as the acid gets converted from liquid to gases (some are the explosive kind!) which takes power....pretty simple. You might have to keep the water level topped off from time to time depending on how much overcharge the battery has been absorbing.
On a low maintenance or maintenacne free battery (keep in mind these were not available when the older motors where made) the construction is slightly different so they do not start to hydrolize when voltage goes up so they create no load on the charging circuit to draw it down, so voltage can go way up, as I sadi I was reading well North of 16 volts at higher RPM's using a low maintenance Marine battery and consequently damaged the Switchbox.
So the battery has been my problem....an expensive problem... overvoltage will destroy your Switchbox, they fry after seeing 16 volts or so input.
I have the right style battery in my ski boat so I switched it and put yet another Switchbox on..Grrrr. I'll run it up and check voltage with my hand held meter.
If all fails then it is straight forward to get a rectifier with a voltage regulator built in, these have a built in load that comes into play when voltage gets to about 14 1/2 volts and therefore do not depend on the battery for this function.
Lesson to all: Use the right battery or swap on a rectifier that has a regulator built in.
I don't have any accessories but if you do they may be voltage sensitive so you might need to use a regulator anyways.
CDI has a rectifier/ regulator combo, later year Mercs had regulators and this is a less expensive part for the same function and they whow how to wire when changing over an unregulated charging sysytem.
Randy

Thank you Randy.
This is very important information.
Neil

I have never heard of this problem. I think its more likely you have a bad connection between the motor and battery.

Some racers used these ignitions successfully with 24 volts with the theory it would work better. I do not recommend 24 volts, but it has been done more than once.


If you are having a repeating failure of the ignition module and its not the battery or battery connection, I would look at the coil as a possible cause.

Hi,
Thanks for checking in here, I assume you are of S&F fame and know these motors. I have all new harnesses external and internal and soldered all connections in the control connections and a new coil although I did switch a few in and out that did not do much. I put a hand held on the battery and when charged it levels off at about 17 volts. I ran it right up to 6000 watching. Everthing seems OK but I am still skitish that I have missed something and doom is waiting for this box.
Two things I remember from when I rebuilt the distributor with a new trigger (Merc NOS) and replaced the bearings,is The epoxy that encases the circuitry had a large high spot that had to be sanded down flush with the housing to clear the chopper wheel. And secondly, When assembled and tightened the chopper wheel was very close the the top (furthest from the housing)of the U shaped pick-up sensor but not touching as rotated around.
I am now wondering at higher RPM's if it's possible the copper wheel may touch the pickup coil in the "U" grounding it as the wheel is metal and the dist shaft would be connected to ground.
Do you think if the pick-up is getting momentarily grounded it would damage the box? I think this would mean the white or black lead on the trigger to the box gets grounded momentarilly. The brown wire shows its OK to get grounded as a shut off.
Maybe there is a small warp in the chopper sheel that goes crazy at a certain RPM and then touches where it should not.
Ideas?
Randy