I have a 40 hp Envinrude with an odd electronic problem. When the boat sits overwinter (in garage) or recently at the boat shop (1 month outside) a problem develops somewhere that prevents the motor from generating any spark. I've bypassed the kill switch, tightened all the connections I could see but none of this seems to work. The problem has occured almost every year for the last 4 years.

For some reason taking the boat to the launch on the trailer seems to correct the problem since it starts at the launch and then continues to run fine for the year. However, this time after the mechanic worked on the prop shaft (hit a rock) the boat won't fire up even after a long road trip. The boat engine operated fine after hitting the rock and was still working when I dropped it off at the mechanics.

Mechanic says he can't work on the electronic problem until next week. Any thoughts on what this could be?

compression is good. Battery is good. Engine is getting fuel.

I believe that engine has an engine fuse that causes the motor to lose spark if it is bad.
You may have a bad fuse, or you may have a bad fuse holder. It would be a good thing to check.

Other than that, you have an electronics pack in that motor that may have finally gone bad.

Take care
REW

A similar thread with same problem.

http://www.websitetoolbox.com/tool/post/outboardwizard/vpost?id=1620953

Take care
REW

This one might fit. However, be sure to check with seller before buying.

http://cgi.ebay.com/ebaymotors/JOHNSON-EVINRUDE-2-CYLINDER-POWERPACK_W0QQcmdZViewItemQQcategoryZ31284QQihZ002 QQitemZ120297376620QQrdZ1QQsspagenameZWDVW

Take care
REW

p.s.
Compare the sellers picture to the power pack on your motor.
If they look the same, it is likely they are the same.

This looks to be the correct one for a 1990 Evinrude - 40hp outboard:

http://www.dixiemarinesales.com/detail.aspx?ID=253

Note the three different possible correct part numbers for this pack:

Take care
REW