1990 Johnson 150 no fire with spark plugs in

[SparkieBoat]

I have a 1990 johnson 150 XP. it gets good fire with the spark plugs removed. when i install the spark plugs i get no fire on any cylinder. The battery test fine, all connections are tight clean. the engine seems to be turning over as fast or faster than any other motor I have worked on. It is not dragging and seems to be well over the 250 RPMs required to start. even when I get no fire the stator is putting out well over 150 DVA on both sets of brown wires, and around 19 DVA on the orange set. I disconnected the big red plug, no change. I disconnected the kill wires going to the power pack, no change. the power pack looks fairly new as does the stator and trigger and the regulator is new. I disconnected the yellow regulator wires and no change. magnets look fine also.
All I can figure is that the power pack is messed up.
Any suggestions?

 

[racerone]

Take the starter apart for inspection.----Use a digital meter and report what it is in OHMS from shaft to the commutator.

 

[SparkieBoat]

Thanks Racer, I did some more searching and apparently they used a gear reduced starter on these models, that can cause this issue. I put another starter on it and whala, we got fire. So it was a result of low RPM cranking. Even though it sounded and looked to be spinning fast enough, I could really tell the difference with the other starter. The starter came off of a older 175 and I assume that it is not gear reduced.

 

[emdsapmgr]

When the engine cranks at least 250 rpm's the ignition side of the stator should put out between 150 and 400 volts as measured by the DVA meter. That's between two wire pairs: brown and Brown with yellow tracer and Brown with a white tracer and it's mate, the brown with black tracer. When the plugs are in, two things happen: 1. typically the cranking rpm's go down somewhat. It may not be meeting the 250 rpm minimum... 2. The plugs require more current when firing under compression. It's possible your ignition system just does not have the power to fire when cranking with the plugs in. Check your cranking rpm's with a tach when the plugs are in. Just for grins, check the cranking voltage on the timer base. Should be 0.6 volts from white to all wires.

 

[racerone]

I do not believe the 150 XP models used gear reduction starters !!