Weak yellow spark

[seadog brian]

Mercruiser 1994 MCM 350 magnum 0F131944
First post, but have been looking for answers here for a month or two. Have followed the TBIV troubleshooting chart, and have changed plugs, coil, wires, rotor, cap, ignition sensor under rotor, and still have a weak yellow spark. Engine will try to start, but only after much tweaking of throttle, starting fluid etc..
Trouble shooting chart appears to be an either/ or chart, but nothing on weak spark.
Have disconnected shift interupter, and tachometer lead, and jumped 12V directly from Battery to coil.
What else to try?
Thanks in advance.

 

[stonyloam]

Weak yellow spark where? Assuming from the coil center wire held near engine metal. The coil is where your spark is generated, so let's start there. You can test the coil by removing the wires then attach a jumper directly from the battery to the coil +, and attach a piece of unsulated wire to the coil -. Briefly touch the - wire to a good ground, when you remove the wire you should get a spark from the coil high voltage wire. See if you get the same yellow, or a nice blue spark. If your spark improves then your problem is not the coil. If your spark improves, repeat with the ignition wire. The reason for a weak spark could be low input voltage, poor ground, or dwell time too short to fully charge the coil.