165hp 470 Mercruiser with no spark

[UNRULEE]

First off hello to all! This is my first post here.

I have a 1987 Larson DC-175 that got handed down to me from my father. I used it all of last summer almost every weekend and it never let me down once.

I took it out of storage over the weekend and went to fire it up and do some maintenance on it and found that it wouldn't start. There is fuel going to it but no spark.

I tried a new coil and condensor tonight, but still no spark, not even at the coil. With the key on there is battery voltage at both sides of the coil. I even jumped the neutral switch (not sure if this is the correct name for it), and still noting. I'm not to familiar with a points style lignition system (I work on diesel engines for a living), and to me the points look OK. Can they look good and be bad. I tested them with my multimeter and they seemed to contact fine.

It seems to me that the points are the only thing left that could be giving me the trouble......or am I overlooking something?

Thanks in advance!!!!!

 

[JustJason]

Re: 165hp 470 Mercruiser with no spark

Did you gap the points by hand/eye/feeler gauge??? If so you need to use a Dwell Meter and set the dwell angle of the points. Gap gets you close, should be close enough to run, dwell dials it in.
Check to make sure you get 12V (or 10 if a resistor is used) at the coils + and ground at the coils -. You can resistance check the coil when it's disconnected. Should get a couple of ohms on the primary, and usually 10K ohms on the secondary. Another thing to do is disconnect the tach, a bad tach can cause a coil not to fire off.

You can download the service manual for your engine in the adults only section.

Welcome to Iboats

 

[BrandonS]

Re: 165hp 470 Mercruiser with no spark

First thing I'd do is check voltage at the coil with the ignition on, should be 12v when on, and 0 when off (this is very important as the voltage kill is what stops the motor). If you have voltage at the coil then I'd check the points. If the contacts are dirty/corroded, you can clean them with some fine sandpaper, or just replace them, they are only about $5 and easy to get. After replacing/cleaning, I would reset the gap. If you don't have feeler gauges you can use a piece of a beer..uh..soda box. To set the gap, loosen the screw that holds the points down, place the piece between the points, move the follower into contact with the cam, tighten the screw. I have never used a dwell meter, and technically shouldn't be needed unless you adjusted the dwell previously, or disassembled the distributor. That should get you going. If not let us know.
Brandon

 

[solar7647]

Re: 165hp 470 Mercruiser with no spark

Welcome! I would suggest that you remove the gray wire from the Neg side of the coil and see if you get spark from the coil. You post suggest that the issue may be the tach and this would prove or disprove this.

 

[UNRULEE]

Re: 165hp 470 Mercruiser with no spark

Well it turns out that I have a bad tach! Thanks to all for the input, I would have never thought of that. As soon as the grey wire would touch the coil it was like turning the key off.


...........now, let's see if I can find a matching "new" tach for the old girl.


Thanks again everyone!!!!!