Mercruiser 170 runs bad when hot - voltage regulator issue?

[gomofast]

So the boat starts and runs fine when it's cold, but after a while, it starts to miss and run very poorly. When this happens, if I then hit the trim (or something electrical), it will completely fall on it's face and lose power. But I noticed that it seems to run fine for a long time if it keep it below 2500 RPMs. Seems like an issue with the coil overheating, but I'm not sure why.

The voltage gauge has always read around 12 volts. But on a recent ride I noticed it was briefly reading 16 volts. I've never seen it that high before. It stayed at 16 for a while and then went back down to 12. All the while cruising fine at 2500 RPMs with no issues.

I know this engine is notorious for issues with the charging system, but I though it's usually that the voltage regulator burns up and stops charging. Does it also have issues with excessive voltage? I'm thinking about swapping out to a pertronix ignition and upgrading to an alternator kit to replace the stator charging system. But don't want to waste my money if there might be some other issue at play.

Thoughts? Any help is appreciated.

 

[Scott Danforth]

you have a points issue and a bad connection issue

start at the battery and work your way to the helm cleaning every connection with 150 grit sand paper making them shiny enough your mother-in-law will eat off them. then file your points, set the dwell, and set timing.

 

[Dubed]

Probably a bad 40 year old regulator. I have upgraded to a alternator and Pertronix.
Do yourself a favor and go with the Breezeworks alternator and keep the points system. The Pertronix is nice but when it fails, you will be stranded. The points, condensor, is servicable and probably wont quit dead on you.
Plus there is a bit of new wiring and deleting ballust resistor, etc. that you wont need to do.

 

[Dubed]

you have a points issue and a bad connection issue

start at the battery and work your way to the helm cleaning every connection with 150 grit sand paper making them shiny enough your mother-in-law will eat off them. then file your points, set the dwell, and set timing.

Yes, what Scott said.
Make sure everything is up to par before you start just replacing parts. My advice is for replacing them if needed.
But I can tell you, it probably should be upgraded before failure, because those regulators dont last forever. Im not so sure if they are still available, if they are, its crazy money

 

[gomofast]

you have a points issue and a bad connection issue

start at the battery and work your way to the helm cleaning every connection with 150 grit sand paper making them shiny enough your mother-in-law will eat off them. then file your points, set the dwell, and set timing.

I replaced the points, and that didn't help. I didn't adjust the dwell or timing, but it was doing this before the points swap.

I've cleaned up several connections, will check some more. But what about the voltage spike?

 

[nola mike]

I replaced the points, and that didn't help. I didn't adjust the dwell or timing, but it was doing this before the points swap.

I've cleaned up several connections, will check some more. But what about the voltage spike?

Yes, failed regulator will cause an overcharge. I'm surprised you got it to start after replacing the points and not adjusting them.

 

[Scott Danforth]

I replaced the points, and that didn't help. I didn't adjust the dwell or timing, but it was doing this before the points swap.

If you don't set the dwell first, you can't set timing

 

[gomofast]

I'm surprised you got it to start after replacing the points and not adjusting them.

I set the point gap at .022, but I didn't do anything else to set the dwell. I don't have a dwell meter, so not sure how to do that.

 

[stresspoint]

you should be showing over 12 volts when running , around 13 is good when cruising @ 2500 IMO.
I'm guessing what you are experiencing when you operate the trim is you are taking too much power from the system to keep enough power to the coil to keep the motor running properly.
point and condenser systems with non resistor coils were notorious for this back in the day when cars had generators. ( turn on the wipers and the motor would stall ).
? do you have an AMP meter connected or a multy meter that you can test how many amps are being drawn as you operate different systems,
you can then run the trim and check what amps are being drawn when you operate the trim.

? what is the condition and age of your battery.

i am guessing your alternator is not up to par or you have a belt slipping .

 

[Scott Danforth]

I set the point gap at .022, but I didn't do anything else to set the dwell. I don't have a dwell meter, so not sure how to do that.

borrow one

 

[gomofast]

you should be showing over 12 volts when running , around 13 is good when cruising @ 2500 IMO.
I'm guessing what you are experiencing when you operate the trim is you are taking too much power from the system to keep enough power to the coil to keep the motor running properly.
point and condenser systems with non resistor coils were notorious for this back in the day when cars had generators. ( turn on the wipers and the motor would stall ).
? do you have an AMP meter connected or a multy meter that you can test how many amps are being drawn as you operate different systems,
you can then run the trim and check what amps are being drawn when you operate the trim.

? what is the condition and age of your battery.

i am guessing your alternator is not up to par or you have a belt slipping .

Yes I think that's exactly what was happening regarding the trim - question was why was the coil being affected in the first place... and seems like it's an issue with the charging system. This engine doesn't have an alternator, just a troublesome stator and voltage regulator setup. I'm thinking that I'm going to convert to an alternator and pertronix ignition. Battery is only a couple of years old.

 

[ROY WILLIAMS]

Yes I think that's exactly what was happening regarding the trim - question was why was the coil being affected in the first place... and seems like it's an issue with the charging system. This engine doesn't have an alternator, just a troublesome stator and voltage regulator setup. I'm thinking that I'm going to convert to an alternator and pertronix ignition. Battery is only a couple of years old.

my MCM470 1978 eng ... I changed stator of the regulator to the alternator did the regulator is higher of 16 volts !!!! did the update back in 30 yrs ....
the Pertronix 25 yrs ago ,,, the ignition coil is positive , running the engine 9.5 volts .... now the Pertronix was a higher voltage of that coil .. did you do that changed it , of that higher voltage of that ignition coil ?
also I was Pertronix ignition and the HP engine is high powered .. did the 20KV spark plugs ....back in old days , the ignition PTS 10KV spark plugs ..
I did the 93 octane gasoline did the Mercrusier of the manual ...THEN changed it around 4-6 DEG ignition OF THE ALCOHOL 10%...
did the recalls ....
you did that 16 volts of that battery LOL ...