120 Mercruiser 2.5L - No spark

[Mercruiser 120]

Hi there. All of a sudden I have no spark. I had the carburetor professionally rebuilt. Hooked it all back up. Lots of gas, I have clear gas hose from the fuel pump up to the carb. Should start right up right, nope. Crank and crank and pump the throttle…Nothing! So I ground my test light and put the other end on the negative side of the coil. I got a light, then a blink, then nothing. The coil has 8V on the + with key on. The engine is a 1972 Mercruiser 120, sorry. The old style white resistors have continuity. I also assumed they were good because I was getting power to the coil. I tried a set of brand new points, gapped them perfectly, then tried three different condensers, 2 were new. I sanded under the points, everything. Where am I going wrong.
How do I test the black wire that goes from the - side of the coil, to the distributor, but the end goes on the screw of the breaker points.

 

[alldodge]

I'm no artist but bunch of wires don't work for me

You have points
Remove all wires off the coil except the distributor (dizzy) wire going to the negative side of the coil

Loosen the dizzy, remove the cap, then turn the dizzy so you can see the points open/close.

That works
Attach a jumper from the battery to the positive side of the coil and crank the motor. Does it start?

 

[Mercruiser 120]

I'm no artist but bunch of wires don't work for me

You have points
Remove all wires off the coil except the distributor (dizzy) wire going to the negative side of the coil

Loosen the dizzy, remove the cap, then turn the dizzy so you can see the points open/close.

That works
Attach a jumper from the battery to the positive side of the coil and crank the motor. Does it start?

Thank you for your reply.
The 2 brown wires that are wrapped and heat shrunk(very nicely) to one connector that go to the - side of the coil with the black one that goes to dizzy, is that the tach wires.
Everything you said. Is that all one task. Unscrew dizzy cap and pull it off I can see the points right there. Don’t undo the dizzy like when I set the timing right?

I won’t be at the boat until Friday morning

 

[Bondo]

Ayuh,..... Down in my signature, you'll see Don's Adults Only Section,.....
Click on it,....
In there are 2 threads on points ignition systems,......
All yer answers are in one of those threads,.....

 

[Scott Danforth]

File the points, then gap the points, then set the dwell

 

[Mercruiser 120]

File the points, then gap the points, then set the dwell

How do you set the swell do you need a special tool

 

[alldodge]

Thank you for your reply.
The 2 brown wires that are wrapped and heat shrunk(very nicely) to one connector that go to the - side of the coil with the black one that goes to dizzy, is that the tach wires.
Everything you said. Is that all one task. Unscrew dizzy cap and pull it off I can see the points right there. Don’t undo the dizzy like when I set the timing right?

I won’t be at the boat until Friday morning

I'm wanting you to verify that the points do open and close. This is the reason to loosen the dizzy, don't remove it. If the points do open and close then they will work.

I want you to hot wire the coil just to find out it does run, disconnect jumper wire to turn it OFF. If it does run, now reinstall as before and find out why it didn't do it before.

The 2 wires to the + side of the coil, one is full 12V when the motor is starting. The other goes thru a resistor to drop the current down to save the points

 

[Scott Danforth]

How do you set the swell do you need a special tool

A feeler gauge set to rough gap the points, a dwell meter to adjust dwell

 

[Mercruiser 120]

I have always set them at 18 thousands and it has worked fine before.
It cranks over, rotor spins around, points open and close but no little spark when they open?

 

[alldodge]

Points don't spark
The points are not grounding the coil when they close or there is no power to the coil. With 12V on the + side and grounding the - side a spark will happen. All the points do is ground the - side

 

[Scott Danforth]

there should not be a spark at the points. that would indicate that the condenser is bad

Just gapping points is close enough to run, setting the dwell with a meter is precise.

ignition dwell is the period of time the points are closed to charge the coil, which then fires when the points open. too little time (to small of dwell) and insufficient charge is built up.

additionally, once you set the points, you have to go back and set timing

 

[Mercruiser 120]

there should not be a spark at the points. that would indicate that the condenser is bad

Just gapping points is close enough to run, setting the dwell with a meter is precise.

ignition dwell is the period of time the points are closed to charge the coil, which then fires when the points open. too little time (to small of dwell) and insufficient charge is built up.

additionally, once you set the points, you have to go back and set timing

 

[Mercruiser 120]

There is my set up. The white wire goes from the resistors up to the + side of the coil. The 2 browns are my tach?

 

[Mercruiser 120]

View attachment 346453
There is my set up. The white wire goes from the resistors up to the + side of the coil. The 2 browns are my tach?

Here is a pic of resistors

 

[alldodge]

In short, for a points distributor there are not enough wires on the + side of the coil, and to many on the - side.

The + side should have at least 2 wires. One for full 12V and one for power thru the resistor.

The - side would have no more then two wires. One for the Dizzy and one for the Tach

Need to trace the wires. Remove all the wires from the coil, then use an ohm meter and check continuity from the resistor to which wire

Also turn key ON and see which wire gets power

 

[Bt Doctur]

dont forget the wire for the shift interupter ,those are the 2 brown ones on the neg side of the coil, interupter and tach

 

[Mercruiser 120]

In short, for a points distributor there are not enough wires on the + side of the coil, and to many on the - side.

The + side should have at least 2 wires. One for full 12V and one for power thru the resistor.

The - side would have no more then two wires. One for the Dizzy and one for the Tach

Need to trace the wires. Remove all the wires from the coil, then use an ohm meter and check continuity from the resistor to which wire

Also turn key ON and see which wire gets power

I thought so . I usually have my shift interrupt or on the negative too but I thought that was the problem

 

[Mercruiser 120]

I thought so . I usually have my shift interrupt or on the negative too but I thought that was the problem

The weird thing is it has worked for 3 summers how it is but would cut out all the time so I thought it was carb and gas issues

 

[Mercruiser 120]

The weird thing is it has worked for 3 summers how it is but would cut out all the time so I thought it was carb and gas issues

Oh sorry. How do you test a little condenser? Touch the condenser and the wire connector where it hooks on the points and check for continuity?

 

[alldodge]

Put meter on high ohm scale. Touch probe to case and lead (must be disconnected). Meter will start low and slowly increase to infinity. This is called a all or nothing test. Your just finding out if its shorted or opened.