install electronic ignition kit in a Mercruiser 120 engine?

[Neutron68]

I believe this is the correct wiring diagram for my engine.  
http://boatinfo.no/lib/mercruiser/manuals/mercruiser1.html#/308

Can you tell which wire color is a key-switched 12V on this diagram?

[Rich_V174SS]

That on-line manual doesn't work right for me, it won't go to the page you indicated unless I go page-by-page manually from the beginning. I don't have to see the manual to know what color wire, I already know it's the purple wire like I've been saying all along. That was also indicated in the wiring diagram I posted.

Here's what I suggest: Try it by connecting the red and black wires directly to the ignition coil, to the positive and negative terminals respectively. If you have any trouble running the engine when power is being used elsewhere then relocate the red wire pre-resistance. Otherwise leave it as-is, plain and simple. What have you got to lose?

[Neutron68]

That on-line manual doesn't work right for me, it won't go to the page you indicated unless I go page-by-page manually from the beginning.

Try copying the web address and pasting it into the address line of your web browser.  
http://boatinfo.no/lib/mercruiser/manuals/mercruiser1.html#/308
That worked for me in Chrome and Internet Explorer.  But, Internet Explorer literally took 30-60 seconds to show me the page.

I don't have to see the manual to know what color wire, I already know it's the purple wire like I've been saying all along.

In the diagram I'm referencing, the purple wire goes to the oil pressure sender.  The wire to the alternator is red/white.

Here's what I suggest: Try it by connecting the red and black wires directly to the ignition coil, to the positive and negative terminals respectively. If you have any trouble running the engine when power is being used elsewhere then relocate the red wire pre-resistance. Otherwise leave it as-is, plain and simple. What have you got to lose?

I could do that, but I'd prefer to wire it up as you suggested earlier, to ensure no problems.

[Rich_V174SS]

In the diagram I'm referencing, the purple wire goes to the oil pressure switch.  The wire to the alternator is red/white.

Take a look on your engine to see if the wire colors match your diagram. You could be looking at a diagram for an older engine pre-1973.

[Neutron68]

I can't look at the engine until this weekend.  It's 80 miles away from me right now. 

The page I'm referencing says it's for Mercruiser 120 serial numbers 3770650 and up.  
My serial number is 4952735, which is greater than 3770650, so it's in the right range.

I converted page 308 to a picture file for you.

[Rich_V174SS]

Ok, if this diagram accurately matches your engine then white is ignition powered by the key instead of purple. The white wire from the harness connector becomes your resistance wire to the coil. The bypass wire from the starter solenoid I think is tan if I read that right.

[Neutron68]

Rich, did you get your web browser problem figured out yet?  If not, please keep trying.  What browser are you using?
That online manual is handy, AND I'd like to be able to refer to a page and have you be able to open up a web browser and look at it, too.

I'll check on the wire colors this weekend.

I thought of needed tool for the ignition upgrade that no one has suggested - a spark plug gapper!

[Rich_V174SS]

Yeah I got it to work, thanks. The manual doesn't open up to the page indicated in the address line but I was able to input the page at the bottom of the screen and go to it that way.

[Neutron68]

I'm glad you got the online manual working Rich!  Now, you can reference a page number and I can go look at that exact same page!

The wire colors matched the page I reference from the online manual. 
The alternator wire was red-white.  The + side of the coil was Tan.  The - side of the coil was black.

I changed the plugs, plug wires, distributor cap, and installed the Pertronix module.  The old plugs were pretty sooty.
The previous owner said the engine was "redone" last year, but the state of the plugs makes me wonder how much they "redid"?
The old sooty plugs were R44T and the 1978 Mercruiser owners manual says it should have R43T plugs.
The marine shop recommended BR6FS, so that's what I just installed.

After it stops raining, I plan to wheel the boat outside and hook up the water earmuffs and start the engine.

When we had the boat out this summer, I noted that the idle when in gear was around 1000 RPM.  The 1978 Mercruiser owners manual says the idle RPM should be 650-700 RPM, so I think I should adjust the idle speed before adjusting the timing.

[Rich_V174SS]

I'm glad you got the online manual working Rich!  Now, you can reference a page number and I can go look at that exact same page!

The wire colors matched the page I reference from the online manual.  
The alternator wire was red-white.  The + side of the coil was Tan.  The - side of the coil was black.

I changed the plugs, plug wires, distributor cap, and installed the Pertronix module.  The old plugs were pretty sooty.
The previous owner said the engine was "redone" last year, but the state of the plugs makes me wonder how much they "redid"?
The old sooty plugs were R44T and the 1978 Mercruiser owners manual says it should have R43T plugs.
The marine shop recommended BR6FS, so that's what I just installed.

After it stops raining, I plan to wheel the boat outside and hook up the water earmuffs and start the engine.

When we had the boat out this summer, I noted that the idle when in gear was around 1000 RPM.  The 1978 Mercruiser owners manual says the idle RPM should be 650-700 RPM, so I think I should adjust the idle speed before adjusting the timing.

Sooty plugs means it's running "rich". Either the idle mix is open a little too much or the carburetor is dumping fuel down the venturies. AC MR43T plugs are equivalent to NGK BR6FS so either are fine.

When adjusting idle speed and timing first get the idle within ballpark and then dial in the timing. If the idle drops too low when setting the timing then raise the idle speed up to compensate. Once timing is set adjust your idle mix screws on the base of the carburetor for fastest idle, again compensating with the idle stop/set screw to keep the idle around 750-800. Then turn the idle mix screws open an eighth turn from their setting to slightly enrich the carburetor, this helps for when the boat is in the water to counter exhaust pack pressure.

[Neutron68]

I believe the idle speed adjustment screw is on the back side of the carburetor?  It sets the limit of a spring-loaded throttle lever, correct?

I think they are showing it in on page 42 (top right photo).
http://boatinfo.no/lib/mercruiser/manuals/mercruiser1.html#/42

And again on page 44 (top left)
http://boatinfo.no/lib/mercruiser/manuals/mercruiser1.html#/44

[Rich_V174SS]

Yep

[Neutron68]

Of note, I was not able to replace the rotor.  The replacement rotor I bought was slightly different from the original (even though it was the correct part number), so it did not lock in place on the distributor shaft, when the Pertronix magnet ring was in place under it.  So, I had to reuse the original rotor.

The rain finally stopped around 3pm Sunday afternoon, so I wheeled the boat out onto the driveway, put the water muffs on and started the engine.  It started and ran!  The idle speed was around 800 RPM. (one tick below 1000 RPM)  I may have misremembered 1000 RPM at idle?

I decreased the idle speed a little, but then the engine was running a little more rough (this with new plugs, new plug wires, new distributor and Pertronix module).  I turned it back up to 800 RPM.  I did not adjust any carburetor jets.

With the timing light I, saw that the timing was 6-7 degrees BTDC at 800 RPM idle.  The 1978 Mercruiser manual says it should be 8 degrees.
I noted that the timing light did not fire with every engine revolution (missing flashes).  
I'm not sure if this was a malfunctioning timing light (which I borrowed) or if there was really a missing spark every so often?
The bolt to loosen the distributor module was in a tight spot and I could not get a wrench on it!!  So I could not adjust the timing.
How can I loosen that bolt??


I took a movie of the engine running at the 800 RPM idle.  
In it, I am questioning whether the engine is running normally?
For reference, the outside temperature is 49 F.
https://docs.google.com/file/d/0B1dmlpYq0PhJbUFhdmE5S05fXzQ/edit?usp=sharing

[Jason]

You can get a wrench on it. You can only turn it about 1/2 flat per turn though. It's a tight fit but doable. Your timing is off a little and might be causing the rough idle too.

[Rich_V174SS]

With the timing light I, saw that the timing was 6-7 degrees BTDC at 800 RPM idle.  The 1978 Mercruiser manual says it should be 8 degrees.

6 degrees is pretty close. What does it say on the info sticker on the side of the valve cover? They have spark plug and timing info listed on the sticker right above your ignition coil.

I'm not sure if this was a malfunctioning timing light (which I borrowed) or if there was really a missing spark every so often?

Spark occurs every other revolution of the crank when the piston is at the top of the compression stroke. If the light seems to be missing it could be because of how the inductance clip is positioned on the #1 plug wire, position can affect its sensitivity.

The bolt to loosen the distributor module was in a tight spot and I could not get a wrench on it!!  So I could not adjust the timing. How can I loosen that bolt??

The best tool to use on that bolt is a 12-point box wrench, I think it's half-inch. Just loosen it enough to get the distributor to move but be careful, your adjustment is going to be ever so slight. Sometimes when you lock it back down the distributor will shift a little and can throw off the setting. It takes a little trial an error but you'll get it. I also like to apply a drop of White-Out with a toothpick onto the timing mark of the crank pulley to make it easier to see against the timing scale. You can also use it to highlight the mark on the scale that you're shootin' for.

After watching your video it seems your valves lifters or pushrods are tapping away something fierce, they shouldn't be making that much noise. Maybe they need to have the valve lash adjusted a bit.

[Neutron68]

The sticker also says 8 degrees BTDC.

[Rich_V174SS]

There are 2 sources that confirm the setting so then it should be set at 8 degrees BTDC.

[Neutron68]

There are 2 sources that confirm the setting so then it should be set at 8 degrees BTDC.

Agreed. 

So, what kind of engine operation would you expect to see/hear if the timing was off by 1-2 degrees? 
Rough idle at 650-700 RPM?

[Rich_V174SS]

A change in timing going from 6 to 8 degrees will increase idle speed slightly. Then you compensate for it with the idle stop screw on the carburetor to get it to your target rpm. A setting of 6 degrees will have a lower overall high speed setting than if it were at 8 degrees, the engine will run better at high speed if the full speed timing is also where it should be. The cause for a rough idle could be caused from a number of things like improperly adjusted idle mix screws on the carburetor, a carb that is flooding or in need of a rebuild, improperly set up valve lash or leaking valves causing cylinder imbalance. I try to shoot for an 800 rpm setting on land because it may drop slightly when the boat is in water due to exhaust back-pressure.

[Neutron68]

When I had the boat in the shop (with the points ignition system) they measured the cylinder compression:
CYL 1 - 162 PSI
CYL 2 - 160 PSI
CYL 3 - 160 PSI
CYL 4 - 154 PSI