Timing too advanced, Johnson 50hp 2-stroke 1996

[janul15]

This is a duplicated post from my previous thread. Summary; Johnson BJ50 BELEDS, difficulty in rotating the flywheel using a usual starting procedure. Advised to check my ignition timing and check the Woodruff key. Results of these checks; Woodruff key present and intact. Ring magnet surface was rusty, so I lightly sanded it to clean it a bit. Timing was found to be well advanced (by about 15 deg.) Now for the confusing bit;, extending the spark control rod, even to its limit, did not change the timing of the spark (according to my use of an ignition timing light). What could be wrong, apart from my poor mechanical skills?

 

[flyingscott]

Get a manual

 

[janul15]

Looked at CDI troubleshooting guide, back to the boat with some ideas.

 

[janul15]

Read on this forum about lapping the crankshaft and flywheel. So I removed the flywheel, cleaned the surface of the ring magnet, took out the key, lapped the flywheel/crankshaft, replaced the key, then replaced the flywheel. This now sits about 2mm lower on the crankshaft. Result; starter now spins the flywheel without previous issues, and timing is now near to perfect.

 

[MarineSp]

Good fix! Lapping the flywheel taper is one of those things nobody thinks about but makes a huge diffrence. The rust buildup on the ring magnet was probaly causing the flywheel to sit slightly high on the crankshaft which shifts the trigger position relative to the sensor — thats why the timing was off even though the woodruff key looked fine.

For future reference on these 96 Johnson 50s, the idle timing spec is around 4-6° ATDC and max advance at WOT should be about 28° BTDC. The spark plugs are QL77JC4 gapped at 0.030" if you havent checked those in a while. Worth doing after a timing issue since advanced timing can cause plug erosion pretty quick on these 2-strokes.