2004 Yamaha 25 hp 4 stroke electrical mystery

2004 Yam 25 hp manual start

Motor runs like a sewing machine for one minute (plus or minus 10 seconds), then starts choogling.

Shut the motor off for 5 or 10 seconds, restart, motor runs like a sewing machine for one minute, starts choogling.

I figure this is electrical because I can't see any significant mechanical changes (i.e. cooling) occuring in 10 seconds. My interpretation is that shutting the motor off resets something that then kicks back in incorrectly after about one minute.

Fuel level in glass inline fuel filter remains constant.

I hope this all comes down to a $5 dollar widget.

Background: oil/filter changed, new impeller, carb cleaned, new plugs, fuel filter looks good, shock treatment with seafoam today.

Any ideas on what could be causing this problem with these clues? Thanks for any ideas.

Also

Also, no bulb pumping is occuring in between starts.

[boats.net]

It could be an ignition problem, problem with prime starter in carb or accelerator pump in carb.

update

I love my neighbor, he looks for simple solutions. Based on his advice, I simply unplugged the prime starter and the motor did the same tricks, butter smooth for 1 min w/prime start unplugged....process of elimination continues...

thermosensor

Ordered a new thermosensor from here and she ran like a sewing machine.

Ran her yesterday with no problems. Planed out once, but ran med. speed due to low water levels.

Ran her today and she did great. Ran up river for probably a minute wide open, then stopped to talk to folks fishing. After about 5 min, went to start her up and the darn thing would not start. Moter was surprisingly hot, but not frying hot. Definitely plan on getting a new water pump.

Why won't the darn thing start now? Stuck thermostat? Thanks for any advice. I thought I had this thing licked.

Update

Brought boat home, cleaned plugs and she started on first pull. Water pressure while running off hose in back yard is excellent.

Took off thermostat cover and pulled thermostat (my first time) and it looks nasty. Am ordering a new thermostat today. Found some interesting little rubber fragments behind thermostat. They are too thin to be impeller fragments. This concerns me.

Also, just when I though this motor was going to be nice, I pulled by dipstick and the oil looks like chocolate milk, with minor gas smell.

I am ordering a new diaphram for the fuel pump, too.

Might should order a new head gasket.

I know I should do a leak down test, but don't have the time right now.

She ran so great up the river Sat, and now I am back to square one. On the bright side, I knew nothing about four strokes a month ago...and now I am getting a crash course. : (