low tension magneto question

[johnyrude200]

I have one of these where there is strong spark on one side, but nothing on the other. I’ve determined that there is nothing coming from that magneto lead (in this case, the top cylinder lead). Does this mean there is a bad condenser and/or the opposite point is not opening at the right time (bottom cylinder point)?

[RICHARD A. WHITE]

Try swapping condensers….plugs, use an ohm meter or Mercotronic, if available to see where the culprit….

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[david-bartlett]

I have had this happen with just dirty points.

[johnyrude200]

This is a motor I’ve built from 10 different donors and am finishing with the ignition, so I’ll swap condensers and report back. The points are freshly installed and clean, so that is where I question if the timing is off on the opposite set or a bad condenser. Back out to do some trial and error and if all else fails bust out the merctronic. (Still trying to find a replacement vibrator for my merctronic, I tried cleaning the points but it still doesn’t work the way it used to).

Every time I work on these, I get less interested dealing with the next low-tension magneto in favor of just updating the motor to accept CD ignition…or in the case of the old 18-20-25’s, reverting back to the universal magneto.

[RICHARD A. WHITE]

Do you have one of Frank’s timing tools????
Absolutely, hands down no better way to set the timing….

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[johnyrude200]

I do, and with this particular motor, I had set the timing using the tool, but after my initial spin of the flywheel to check for spark, realized that the last guy had installed a 9.5HP flywheel key into this 15hp motor. So it was completely wrong. Just got some NOS 9.9/15hp flywheel keys in today and installed, so may need to reset the timing before going any further.

Will report back with findings hopefully later tonight or mid day sunday!

[frankr]

Breaker points are the biggest troublemaker on those mags. BOTH sets of points have to be making contact for it to work, unlike a Universal Mag that will run just fine on one set of points (on one cylinder). If you think the points are clean, check them again. And make sure you get zero resistance across them when closed. Not "almost" zero, but zero.

[johnyrude200]

Figured it out, timing was wrong due to the wring flywheel key havibg been reinstalled, and coil #1 was no good.

On a side note, I had a customer bring in one of these same motors (’76 15hp) where he says it dies out after 3-5 mins at WOT throttle. Im guessing condenser(s) on that one? Says after sitting for some time it starts right back up like nothing is wrong, but when it dies nothing can get it restarted.

[fleetwin]

The other thing to be aware of on these engines is the pesky little primary harness that runs from the mag plate out to the coils….The harness gets sliced/split/chafed and grounded….
On the 76 15hp, when customer says it dies out, does that mean it stalls out? Could be overheating/seizing/not enough oil as well…
Could be something as simple as an air leak in the fuel line, etc…
In any event, I wouldn’t attack that ignition system until you have run the engine, duplicated the problem, and confirmed there is an actual ignition problem…Again, could be something as simple as a bad plug….
Seems unlikely that both condensers are bad….

[frankr]

Speaking of bad plugs…But I guess I’ve ranted enough about the plug problems in those engines. Some of them wouldn’t run one weekend without fouling plugs.

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