Reply To: Thrust, hp, and weight comparisons

[Charles Myers]

Thank you for your continuing help.

The first sentence of your last message is interesting.  While the “mag arm” is all the way at its stop, I have been setting the collar on the throttle rod all the way back while the throttle rod is pushed all the way forward (opening the throttle butterfly fully).  Am I doing that wrong?

During all my efforts, I got tired of walking all the way forward to the remote gear and throttle levers while working on the settings.  So at the motor I detached the push/pull gear cable and the push/pull throttle cable to make the throttle setting manually.

At one time, I considered the possibility that the throttle notches might have been “off” in the remote control box, but as it happens, the max throttle lever position on the remote places the push/pull cable for the throttle in exactly the same spot as setting the max by hand.

From your comment, I gather that the failure of the  “mag arm” to reach its stop during maximum throttle affects timing and may account for why the motor does not run fast enough at maximum throttle.  Am I understanding that correctly?   A clue may be as follows: A Johnson Service Manual says that the pivot for the “mag arm” includes a spring (304220) that may not be strong enough to advance the “mag arm” all the way to its stop and that a revised/ stronger spring (304656) should be used.  I have the stronger spring on order.  Unfortunately, installing it probably will require removing the flywheel – which I have been unsuccessful doing so far.  Pulling the flywheel off is scary.  I have a substantial fear of cracking the flywheel or stripping out some threads while trying to pull it.

Another theoretical possibility for the problem is that the throttle cam may be out of position.  It is bolted in place by two tiny bolts reaching UP from the bottom of the cam.  Synchronization instructions say to loosen those bolts and to move the cam to enable the roller to touch the cam in the right place.  Getting a 5/16/ wrench on those tiny bolts is really difficult, and I have tried that, but I don’t dare to loosen the bolts so much that they fall out.  But, so far, the loosening that I have done seemed not to enable repositioning the cam at all.  So I re-tightened the bolts.

A third possibility, (not likely, I believe) is that the gearing at the base of the vertical throttle arm is off by a tooth.  I can remove the vertical arm, but it has a rectangular base that fits into its socket only one way, and I don’t see a way to adjust the throttle gear to mesh with the vertical arm in another gear notch.