Low voltage to coil

[bone9999]

I have a question regarding the electrical side of a 1982 40 hp Mercury -

First off, the motor has been pretty much gone through already and is running pretty good for being 30 years old. The stator and trigger both check out good for resistance and DVA voltage. The switchbox is new, because the old one seemed to be bad by process of elimation. By the way replacing the switchbox did fix the idling and power issue. Both old coils check out good for resistance, however one had a good amount of oxidation internally so it was replaced with a new one.

Now with everything else checking out good i am still only showing ~2.5 volts on both coils from the new switchbox, this is checking at the switch and at the coil. The spec for this system is ~150v using a DVA. This was also the case with the old switchbox.

What i really dont understand is how i have a good spark, the engine starts quickly and runs good but is getting such a low voltage between the switch and coil. I know the DVA works and is accurate, as i can pull good readings from the other components. I have also pulled readings to the coil while the engine is running, turning over, and plug wires disconnected all with the same result.

So does anyone have any ideas or am i a dumb@#$ and doing something completely wrong?

 

[aussieflash]

Re: Low voltage to coil

I would re-check the trigger coils and connections.Check inner magnets on flywheel.Also check your rectifier is operating correctly with an OHM test.

 

[bone9999]

Re: Low voltage to coil

Thanks for the reply aussieflash.
I will re-check the trigger and rectifier this evening when i get home and post the results. As for the magnets, they are in good shape and in the correct position - 180 degrees apart.

I should also add that I have already replaced a good amount of the wiring on the motor due to the old being very degraded.

 

[bone9999]

Re: Low voltage to coil

OK, so the rectifier tests out good. trigger is also testing out good - brown/white to brown yellow - 880 ohms and ~7 volts while cranking. brown/white to ground is also as it should be. Went ahead and retested the stator and it checks good as well - black/yellow to ground is ~250 v while cranking and black/white to ground is ~28v.

I also rechecked voltage to the coil with both an analog and digital meter and came out with similar results - ~2 to 3v. The odd thing is i have to switch the positive and negative leads on the analog meter to get a positive result.

Correct me if im wrong but it seems to me that if the stator is putting out the correct voltage and the switchbox is new(and works as it should) then there should be much more than 2 volts going to the coil.

 

[oldman570]

Re: Low voltage to coil

The main perpuse of the coil is to incress the voltage from the switchbox enought to fire the plug with enought voltage to work under compression. Therfore if the plugs are firing and the spark will jump a 1/4' to 7/16 gap with a spark tester everything should be good. You have to remmber that high voltage creats heat and switchboxs dont like heat. That is why switchboxes are mounted away from the block and have air flow around them.
Oldman570

 

[bone9999]

Re: Low voltage to coil

Well i think i may have found the problem. I had been testing the voltage of the stator while disconnected from the switchbox, which was giving me good readings of +200v on black/yellow. I have now tested the voltage while it is connected to switchbox and now the stator only shows ~4 - 5 v on the black/yellow. The black/white is still giving good readings of ~28v while connected.

Does this mean the stator is bad/weak?

The way im understanding the CDI troubleshooting guide this would indicate a bad switchbox, however it is brand new.

 

[bone9999]

Re: Low voltage to coil

Thanks for the help so far, but does anyone else have any input on this?

Had it out last night- the bogging issue is back, which i had before replacing the switchbox, and both plugs fouled fairly quickly. Motor starts and idles just fine however in gear there is very little power to plane out.

 

[bone9999]

Re: Low voltage to coil

In case anyone needs the info the switchbox is faulty. Called CDI for help troubleshooting and we determined the switchbox was in fact the issue.

Now for my next question - I am showing ~0.2 v or less through the kill switch wire (while disconnected from switchbox) when the ignition switch is turned on. The voltage also disipates to <0.015v very quickly while leaving the switch on.
Could this be causing the switchbox to short?