1983 4.5 Evinrude bogs down after running wide open

[fishguy]

4.5 Evinrude on a small, light car-topper. With 2 people in the boat, it plows along and labours all day, no problems. With just me, sitting halfway in boat, it'll plane and scoot right along. Trouble is, after about 5 minutes of running on plane it starts to slow down...then comes off plane, and will run slower and slower. I have to let it idle for 2-3 minutes, then it will take right off but bog down again after 1 minute on running on plane. <br />When this is happening, one plug is fouling. (Can't remember which one, it's been winter for too long...)<br />I'm convinced it's ignition (coil breaking down..?) On the last day of the season I flipped the works upside down in salt water..Got to shore, pulled the tank, flushed it, stripped the carb down, etc etc. Took it back out and it was doing the exact same thing. So, that was one way of getting around to pulling the carb off and cleaning things up. <br />Water pump is working, and only seems to happen when it's just me in the boat and it can open right up. 2 people in boat, WOT all day, tank after tank, never miss a beat. Plane for 5 minutes, bog bog bog.<br />I should also mention that it worked great up until the middle of last season, so it's not a 'nature of the beast' thing.<br />Sorry for the long post, but the more info the better, right?

 

[alcan]

Re: 1983 4.5 Evinrude bogs down after running wide open

The condition you describe is usually do to lack of fuel. Causes include, tank not vented, air leaks, fuel pump, carb float adjustment.

 

[fishguy]

Re: 1983 4.5 Evinrude bogs down after running wide open

I should mention too...I tried swapping spark plugs, and the problem is happening on the same cylinder, and not following a bad plug around.<br /><br />When it starts bogging, if I stop and sit a bit, the time is tames before the problem happens again is proportional to the amount of time I sit and idle...(The longer I sit and idle, the longer I'll be able to go before bogging again) If I sit and idle for 15 seconds, I'll be able to go for about 30 seconds before bogging. If I sit and idle for 5 minutes, I'll be able to go a couple minutes before bogging.<br />I've tried running without the engine cover (thinking lack of airflow), and running without the fuel cap. Fuel lines are good, filter is new (replaced when I drowned it). <br />Is there an ignition component that could heat up and cause a misfire in one cylinder? <br />I'd like to hear from a tech who's seen this before, as I don't have anough $$$ to take it to a shop and let them diagnose and spend a lot of $$ replacing parts until something fixes it. Also, would be hard to diagnose, as it only fails out on the water, on plane.