1974 seawirl ranger merc Cruze 4cyl

[Deeshawn]

Hey I’m new here I have a four cyl no spark but have power to coil could it be my resistor?

 

[achris]

Hey I’m new here I have a four cyl no spark but have power to coil could it be my resistor?

Hello and welcome to iboats...

Yes it could be the resistor, or a thousand other things.

Let's start with what you are working on. We don't need to know about the boat, just the engine (the engine and the boat aren't made by the same people, so the boat is pretty much irrelevant).

Can you give us the engine year, model (120, 140, 470, etc), the engine serial number, and as you're working on the distributor, if it's points, electronic and any other information that might be relevant...

Chris...

 

[Deeshawn]

Hello and welcome to iboats...

Yes it could be the resistor, or a thousand other things.

Let's start with what you are working on. We don't need to know about the boat, just the engine (the engine and the boat aren't made by the same people, so the boat is pretty much irrelevant).

Can you give us the engine year, model (120, 140, 470, etc), the engine serial number, and as you're working on the distributor, if it's points, electronic and any other information that might be relevant...

Chris...

It is a MerCruiser 120 horse inboard motor

 

[Deeshawn]

It’s a 74 MerCruiser four-cylinder it’s got points with an external resistor I replace the coil points cap rotor spark plugs I have replaced the ground there’s not much more I can think of

 

[nola mike]

Did you set the dwell and timing after you replaced everything? First thing to check is to see if you're getting 12 volts at the coil positive terminal.

 

[Bondo]

Did you set the dwell and timing after you replaced everything? First thing to check is to see if you're getting 12 volts at the coil positive terminal.

Ayuh,..... While crankin' on the starter,...... just the key "On" should be more like 9v,....

 

[Deeshawn]

Did you set the dwell and timing after you replaced everything? First thing to check is to see if you're getting 12 volts at the coil positive terminal.

How would I do that?

 

[nola mike]

Ayuh,..... While crankin' on the starter,...... just the key "On" should be more like 9v,....

Yup, forgot about the resistance wire. 12v cranking, 9ish with ignition on.

How would I do that?

Which part?

 

[Deeshawn]

Thanks guys I have figured it out!

 

[j cat]

It’s a 74 MerCruiser four-cylinder it’s got points with an external resistor I replace the coil points cap rotor spark plugs I have replaced the ground there’s not much more I can think of

turn the key on no cranking ,,, voltage on the ignition coil + is 9.5 volts dc to the resistor..
then crank the engine and the voltage at the coil is 12 volts [ FROM starter motor]...cranking !!!
also you do the points around .022 and use a dwell meter to crank it ...
also pull the spark plug wire off use a spark plug , clamp the ground clamp on the socket plug area, then crank it and see if the spark is a bright white spark..
dwell 31-34 deg, resistor to coil + 1.2 -1.5 ohms,,, points .022 gap. timing is 8 deg.
look up the - ignition coil see if the ohms are zero ohms to ground... if it is grounded then the shifter switch can ground the neg coil ...probably the brown wire to the shifter switch ..engine will not start...

 

[achris]

turn the key on no cranking ,,, voltage on the ignition coil + is 9.5 volts dc to the resistor..

Incorrect!

If the points are open, the voltage at coil+ will be full battery voltage, approximately 12.6v.
If the points are closed, the voltage on the coil+ will be approximately 7v.

Chris....

 

[j cat]

Incorrect!

If the points are open, the voltage at coil+ will be full battery voltage, approximately 12.6v.
If the points are closed, the voltage on the coil+ will be approximately 7v.

Chris....

I have my mercrusier manual 1974 120HP I have all his engine spec.
you are not correct I got the manual period ..
you are not using the correct info ...

 

[achris]

I have my mercrusier manual 1974 120HP I have all his engine spec.
you are not correct I got the manual period ..
you are not using the correct info ...

OP, please ignore this post. It is completely incorrect. I say that as an electronics tech of more than 40 years, and a certified Mercruiser technician.

Chris...

 

[Scott Danforth]

installing/adjusting points

pull points out of package
file the points
install points in distributor
make sure to oil the lube wick
install new capacitor
rough gap points with feeler gauge
adjust with dwell meter while cranking the engine
install cap and wires
fire up engine and set timing.

 

[kenny nunez]

How long have you had this boat? When was the last time you have known the engine to run?
Does the distributor shaft rotate when trying to start? If yes remove the grey wire from the distributor or negative side of the coil leaving the black wire attached. Spin the engine over and with the coil wire 3/4” from the engine is there a spark? If yes then either the shift interrupter switch is engaged or very rarely the tachometer or the wire leading to it is grounded.
An engine this old probably has a well worn out distributor, with the points closed grab the rotor shaft and try to open the points, if yes then it should be rebuilt with new bushings. Most times the engine will run with a worn distributor but not as good as one with a rebuilt distributor.

 

[Scott Danforth]

Napa has new bushings in-stock. one is about $5, one is about $8