Mercury 850 even cylinders no Spark

[hoffmanuno]

We have a 1963 mercury 850 that only fires on #1,3, & 5 cylinders. We installed new condensers and cleaned and reinstalled the points. We swapped out coils between banks and isolated the ressistors but this did nothing. We checked the points with a voltage tester and both sets of points checked out with power and showed that both sets of points were opening and closing with the voltmeter (meter moved back and forth on tester as the opened and closed when we spun the flywheel by hand). We are reasonably sure that by swapping and isolating both coils and resistors that these are not the problems. We did not have the proper tools to set points at proper spacing. We tried setting the points for the odd firing cylinder banks numerous times but this did not work. Briefly we did experience some very occasional sparks on all odd cylinders, when engaging the starter for 5 seconds but this only worked once or twice and then it did not do it again. We swapped out the condensers between odd and even banks and this did not help either. We have very strong consistent spark on the odd cylinders but nothing on the even ones. We swapped coil wires as well. We read that maybe if our points are not adjusted right that could cause too low a voltage to build up in the coils. We have no gas hooked up but did squirt some gas in carbs and it turned over for a second on the odd cylinders firing. The points are not new, but their surfaces are clean and we have a new rotor installed. Please give us some advice o wise men of the mountains, we are but simple backyard mechanics who rebuilt an old motor.

 

[emckelvy]

Re: Mercury 850 odd cylinders no Spark

Re: Mercury 850 odd cylinders no Spark

Perhaps the one-half of the rotor which sparks the other 3 cyl's is grounded.

A good way to tell this is to pull coil wires out on both coils, and check for spark directly out of the coils, not at the spark plugs.

If you're getting spark at both coils, but only on odd/even plugs, sure bet the rotor is bad.

As long as the points are clean and adjusted to between .008"-.010" it should spark and run well enough. It'll run better if you set the dwell on the points but that in itself won't stop the spark.

HTH and let us know what you find...........ed

 

[hoffmanuno]

Re: Mercury 850 odd cylinders no Spark

Re: Mercury 850 odd cylinders no Spark

Perhaps the one-half of the rotor which sparks the other 3 cyl's is grounded.

A good way to tell this is to pull coil wires out on both coils, and check for spark directly out of the coils, not at the spark plugs.

If you're getting spark at both coils, but only on odd/even plugs, sure bet the rotor is bad.

As long as the points are clean and adjusted to between .008"-.010" it should spark and run well enough. It'll run better if you set the dwell on the points but that in itself won't stop the spark.

HTH and let us know what you find...........ed

 

[hoffmanuno]

Re: Mercury 850 even cylinders no Spark

I havent gotten a chance to try and test the coils as you have suggested, but I had purchased and installed a brand new rotor. I now have an old rotor in good shape that I could swap out, but this new one is right out of the box from oldmercs.com.

 

[hoffmanuno]

Re: Mercury 850 even cylinders no Spark

I figuired it out. It was the points. One set of points wasn't closing, it looked like it was very very close but hard to tell on the motor. I took off the lower distributor, reset the points, and it fired on all six. This was the exact same problem it had when I got it. While I have good spark now, I will be buying new points as soon as I put our rebuilt motor thru some break in trials to test the motor out. It was worth the time spent diagnosing however, because now we know for certain that my coils, condensers, resistors and wiring are all in perfect working order. Thanks for your help everybody.