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85 PCM 351 losing spark as rpm's increase

Greetings!

I'm working on a Nautique that idles great and motors smoothly out of the marina. As soon as you begin to put her under a load the engine begins to stumble and not pick up speed. Increasing throttle causes the motor to lose power.

The only thing that I have noticed occurring is when I hold the coil wire just out of the center of the distributor cap while the engine is idling I can see a nice, strong, blue spark jumping the air gap I've created. There is an audible "snap" every time the spark makes the jump. As I begin to increase rpm's, the spark begins to fade and the sound begins to diminish to the point where I have to push the coil wire further down into the cap in order to keep the engine running. It appears as though something may be wrong with the ignition system because I'm pretty sure the spark should stay strong and blue throughout the rpm range.

Here's what I've done -

Compression test good
Engine vacuum test good
Cap
Rotor
Plugs
Points
Condenser
Wires
Coil
Coil Resistor
Ran 12v to the coil direct
Made sure no other wires were connected to the coil like the tach
Added an extra ground to the distributor and the motor
Removed the distributor plate to look for a broken braided ground strap, none
Checked operation of the distributor weights, good
Added a squirt of starting fluid to the carb while the engine was missing in case of a carb issue, no change
Advanced and retarded the distributor by hand while engine was missing, no change

Short of upgrading to an electronic ignition I can't think of anything else to try. Thanks in advance for any help you can give. I'm so over it right now. :)
 
ignition switch isn't on your list....and it may be easier to execute a trial with a fused jumper straight to the ballast....

I would also make sure the timing advance is functioning correctly my measuring the curve....
'operation of weights' != correction function provided...
 
Thanks for your reply makomark.

I ran a 12v lead from battery positive to both sides of the resistor and directly to the coil with no change. I went ahead and used a timing light today and timing is advancing. I hadn't used a timing light before because I assumed advancing the timing by hand at 2k rpm's with the engine missing was esentially doing the same thing. No change in pattern at all. :rolleyes:
 
A short dwell angle will limit coil saturation, and will cause a weak spark at the higher RPM range.
Do as Mark suggests, and use a dwell meter when adjusting the contact points.
 
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