Marine: Boating, Sailing, PWC, GPS and Navigation - Evinrude 150XP starts cold, runs fine, until...

I have a 1989 Evinrude 150XP that starts cold and runs fine until it's shut off and restarted. I can idle, race WOT, or cruise from a cold start however, when I shut it off for just a few minutes (sometimes shorter), it loses power and stalls as I increase throtle while in gear only. I found if fiddle with the throtle stick (as to not let it die), it eventually (rather suddenly) regains it's otherwise good performance and again will run all day. When it is in this troubled state it will idle fine and increase throtle when in neutral, just not in gear. The engine pan is clean and dry. Infact, 2 years ago the fuel lines were replaced and the carbs were rebuilt. I've pulled the plugs and all of them look the same with little wear. - Any ideas??? Could this be a choke solenoid or primer? Perhaps a check valve or something in the fuel pump?

the mag advance under the flywheel could be sticking.
or some of the stator potting mix may be oozing on it and
causing it to stick.
Is it charging? does the tach work? can youb easily move the
mag advance manually?

Yes it is charging and maintains a pretty good 13.5 to 14 volts. I understand what you're refering to about the mag advance... Evinrude calls it QuickStart. In fact I thought of that but how can you check it manually? Isn't that all crammed up under the flywheel? I can't imagine how I would check that without taking the flywheel off. Please continue...

with the cover off have someone advance the throttle to the wot position
with the engine off. watch that the throttle plates open and that the
magneto advances with the lever. you will see that it is spring
loaded and can pivot freely under the flywheel.