1974 mercury 1150 - no spark

J

jdonald

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Aug 21, 2010
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Motor was running perfect last season. This year we installed a new battery that spins the motor fast -would not fire - no spark. I need a trouble shooting chart with electrical values to trace the problem. ( ohms across coil primary is almost 0 ohms) Can anyone steer me in the right direction? (my kids want to go skiing and summer is passing) Thanks, Jim
 
M

Moody Blue

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May 24, 2004
Messages
3,136
Re: 1974 mercury 1150 - no spark

First thing to check is voltages at the switchbox.

Non-distributor side of switchbox.

Key OFF.
+12V at red terminal
0V at all other terminals

Key ON
+12V at red terminal
+12V at white terminal


Check these out and post back with results.

Coils rarely go bad.

Post a S/N of the motor to confirm the year.
 
J

jdonald

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Aug 21, 2010
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Re: 1974 mercury 1150 - no spark

serial #- 3761333
voltages check out as described

I jumpered white/ brown wires on dist. side of module - grounding black wire did not induce spark on coil wire

Voltage while cranking is 9.6 on red and white wire on side opposite dist.

no voltage on green wire while cranking

rotor turns while cranking (belt not broken)

Thanks, Jim
 
M

Moody Blue

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Messages
3,136
Re: 1974 mercury 1150 - no spark

jdonald said:
serial #- 3761333
voltages check out as described

I jumpered white/ brown wires on dist. side of module - grounding black wire did not induce spark on coil wire

Voltage while cranking is 9.6 on red and white wire on side opposite dist.

no voltage on green wire while cranking

rotor turns while cranking (belt not broken)

Thanks, Jim
Click to expand...

Hope you disconnected the distrib wires before jumpering as you described. If not, you probably toasted the trigger circuit in the distrib. Where did you have the coil wire when checking for spark?

Cranking voltage is about right.

Do you have a mercury tilt switch still connected to the switchbox? If so, disconnect it, it may be faulty.
 
J

jdonald

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Aug 21, 2010
Messages
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Re: 1974 mercury 1150 - no spark

Yes, I followed the directions on another post I found on this site and disconnected trigger wires first.

I tried jumping the spark to several different places to make sure I had a good ground. There was no hint of a spark on the black wire I was grounding to induce the spark. I left the "capacitor?" hooked up on the brown wire post for the test.

What and where is the tilt switch?

Thank you again, Jim
 
M

Moody Blue

Captain
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May 24, 2004
Messages
3,136
Re: 1974 mercury 1150 - no spark

What you referred to as the "capacitor" is the tilt switch.
It is a mercury switch that shuts down the ignition if the motor is tilted too high during operation.

If that switch has gone bad, it may be disabling the ignition system. Disconnect it to be sure its not the problem.
 
J

jdonald

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Aug 21, 2010
Messages
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Re: 1974 mercury 1150 - no spark

When I disconnect the tilt switch - key on - 12V at red and white terminals on non dist. side.

Brown and white jumpered on dist. side - momentary connect of black post to ground - No spark on coil wire.

Is the switch box probably shot?

This switch box is a used one that came off a 4 cyl. merc. about 15 yrs. ago.

There must be some latitude in what model and year motor the switch box comes off of?
Thanks, Jim
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
29,036
Re: 1974 mercury 1150 - no spark

It sounds very much like the switchbox is bad. Most 4/6 cylinder 70s merc switchboxes are compatable.
 
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