1976' 75HP Evinrude Engine Bogs Intermittently

[davidm123]

The motor starts fine and runs well for a while. Tops out at 36 MPH with light or heavy loads on a 16' alum. hull. After a while, 15-20 mins, the motor will bog down and slow to about 20 mph. Sometimes it does this at throttle up, motor won't push boat out of the hole.

I've had this engine for 2 seasons and have had this problem just as long. A trip to the local Johnson/Evinrude guys here in Rochester discovered that the carbs were not correctly synchronized. They corrected that and I still have the same problem. Secondly, they also mentioned that I should be using 89 octane because today?s gas is "inferior" to what was used in 1976.

The upgrade to 89 octane fresh gas did nothing, and octane boost did not help.

My tank vent is open.
Fuel screen is clean.
plugs are clean and gapped correctly.
Engine low idles very well.
Starts Instantly every time.

What else could cause this? Would like some ideas before another $$ trip to the marina.


Oh yeah, backing off the throttle for a second seems to help some of the time.

Thanks

 

[jtcarter]

Re: 1976' 75HP Evinrude Engine Bogs Intermittently

I would be looking in my ignition system. Sounds like something heating up and breaking down.

 

[Randybeall]

Re: 1976' 75HP Evinrude Engine Bogs Intermittently

Have you tried pumping the fuel bulb during the break down. You could have a fuel pump problem or even a strainer in the fuel tank pluging up. Second guess would be something in the ignition heating up and fading out. I don't give that as much thought because of you comment that backing off sometimes helps the problem. That suggests your carbs did not have enough fuel and closing the throttle let the pump catch up.