40 Hp 3 cyl Mariner 1998 Power loss after approx 30 minutes of use

Mav23rick · #1 August 17th, 2006, 02:24 PM

Mariner/Mercury 40 HP 3cyl E. 1998. Plugs good, gas good, fuel pump OK, filter replaced... Looses power after initial good performance at full speed, (30 to 40 min.). Upon the next start-up, the motor will go to full power. While the motor is at full throttle an running slow, I push in the electric chock in and get an initial burst of power then back to slow speed. I've pumped the gas bulb with no effect. I have not done the heat test with a dryer. I was just wondering if anyone can tell me what they did to correct their problem?
Thanks, Mav...

Mav23rick · #2 August 17th, 2006, 03:04 PM

CORRECTION:
Upon the next start-up, the motor will "NOT" go to full power...

Can anyone help? I've got twin girls that want to ride a tube...

Mav23rick · #3 August 17th, 2006, 03:35 PM

Me Again... I have the exact described problem as JP:

Problem: motor runs great at various throttle positions including full speed (5000)rpm for 10 - 20 minutes or so after initial startup but then suddenly cuts back to about 3400 rpm at full throttle. Once the motor starts this behavior, it will not run at full rpm (5000)without coaxing. I did discover that the engine will run at 5000 rpm if I manipulate the electronic push button choke intermittently.

Can anyone help?

Texasmark · #4 August 17th, 2006, 08:31 PM

I had a '75 70 hp OMC that did that and it turned out to be the thermostat sticking closed. You could start it and run it for the first few 10's of minutes and it was a darlin but after awhile it started running rough and wouldn't perform the same.

Finally, one day, at WOT it froze shut. Cost me an overhaul.

Mark