1150 won't fire, no spark, erratic spark

bruchester

Cadet
Joined
Apr 8, 2013
Messages
24
A 73 1150 inline six (s/n 3527319) Thunderbolt ignition just won't fire-need some troubleshooting guidance. As detailed as I can be.....

Here's what I've done so far:
1.most wires very ratty, so have replaced as much as possible. It appears that one, at least, coming from the harness, inside lower cowl is questionable, but I believe its serving its purpose and don't think its the prob. Two wires going to the top and under the flywheel were repaired with new wires up as far as I could go, where they enter the 'grommet' at flywheel they were in pretty poor shape and very close together-could be an issue. Wasn't ready to remove flywheel as to screw up timing and not knowing if what I found under there would be repairable.

2. first thing I checked was distributor cap and rotor. Inside of cap was damp and grungy, but cleaned up pretty well. Rotor was fair, but did show some minor burnt on one of the two 'tines'. Trigger disc above cap was covered in green oxidation (its copper, I surmise), so I used a razor blade and fine sand paper to clean up pretty well. To get the top of the disc, I slipped the fine sand-paper in and did the best I could while rotating the flywhee to spin it around a bit.-HOPE THIS DIDN'T CAUSE DAMAGE OR A DUMB MOVE!

3. Engine cranks well with starter fully functioning. Had my buddy checking for spark and while cranking has, basically none in what, I sense should be a regular spark. Plug will generate a sloppy, weak spark when 'clicking' ignition on to off while trying to fire.

4. Had to open the MerControl as it was jammed up and noticed some rotten wires tucked way down in there. Haven't repaired them yet, as it seems to be engaging the starter and choke well enough to believe its not shorting out in there-but question whether this could be an issue with getting it to fire-I believed not-but expert might know better.

5. Tried to test the coil using Clymer manual, but a rookie using my multi-meter and wasn't too sure of results. My pal will be bringing his meter that he knows how to use to run this test again.

Can't think of where next. Motor ran strong and reliable all last season, rectifier has been replaced about two years ago-not sure that would be the issue anyway.

All help and advice welcome and appreciated!

bruchester
Pittsburgh, 72 Glastron V173 Bayflite w/73 Merc 1150-6
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,267
Re: 1150 won't fire, no spark, erratic spark

That motor must have +12VDC on the red and adjacent white wires on the switchbox, in order to have spark. Spark plug and coil wires screw into distributor cap. Rotor does not come off dist shaft, but it will break easily and set you back $200Plus.

Troubleshooting test will isolate issue.
 

bruchester

Cadet
Joined
Apr 8, 2013
Messages
24
Re: 1150 won't fire, no spark, erratic spark

ThaNks Chris. So, should I put the meter on both switchbOx terminals, crank and look for 12V? Or put red probe on switch box terminal, other to ground and check each terminal that way, while cranking?

Thanks
 

bruchester

Cadet
Joined
Apr 8, 2013
Messages
24
Re: 1150 won't fire, no spark, erratic spark

update: Checked red and white wires on swithbox. Battery connected, ignition off probe(s) on red and white-got 12.4VDC. So a good sign. Going to pick up a spark tester and check spark at each plug. Did discover a small, very thin crack on rotor in addition to small burnt spot on one tine. A suspect.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,267
Re: 1150 won't fire, no spark, erratic spark

Just to be clear, +12 voltage should be on red wire and ground, all the time. White wire should have +12VDC on it (to ground), when ign key is in run or start position.
 
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