Need help diagnosing mysterious malfunction on Evinrude 40 hp

I have a 1986 Evinrude 40 hp electric start with a throttle control column and steering wheel. It has worked perfectly for 3 years and the compression was recently measured at 140 for both cylinders. I have been wanting to have the VRO oil injection system removed so I don’t have to worry about blowing the engine. When I took it to a very reputable mechanic who specializes in older engines, he said, “Yep, the VRO has got to go.” So I have him remove it. That’s when the trouble started.

* On my first trip back on the water, the engine worked perfectly on wide open throttle for about 20 minutes as I ran around the lake testing it. Then I stopped to fish for a half hour and tried to start it up again. This time it started fine, but it began to lose power. It was surging up and down when I pushed it to WOT. Then it would only run at about 1/2 power as I limped back to the ramp.

* I took it to the mechanic and he said that there was a defective “needle” in the carb that he fixed. It ran fine for him in his testing tank.

* I took it back out on the lake. It ran fine for about 30 minutes on WOT as I ran around the lake testing it. Then I stopped for about 45 minutes and fished. When I went to restart it, it would only go to about 1/2 power when I pushed it to WOT. The motor idled fine and sounded fine when it was idling. It just wouldn’t go to full power. I decided to let it sit for 2 hours to see what would happen so I fished and waited. After two hours, it started up and went to WOT just fine and I ran it around the lake for 25 minutes on WOT. Seems like it runs fine if it has been sitting in my garage or taking a rest on the lake for 2 hours.

What could be causing this? The mechanic recently installed new spark plugs when he removed the VRO.

Try a new hose. The older Evinrude hoses flake off within the hose and you could be pumping those flakes through.

Ya sounds like a fuel issue choking out or a vaper lock somewhere. Take the mechanic out for a 30 min ride, then when it happens he can check it out.

First mistake was removing the vro.

The VRO worked for 35 years so you removed it so you didn’t have to worry about it wrecking your engine?

TheFamousGrouse wrote:

The VRO worked for 35 years so you removed it so you didn’t have to worry about it wrecking your engine?

I agree with Grouse, WTH man, did they have a valid reason for taking it off??
kits for those things are around 150 bucks if the plastic housing isnt warped there is zero reason to disconnect it.

sadly, my first question is,,,, did anyone remember to mix the oil and gas before you took it out?? if you are still running on straight gas that motor is fubar.
take it back and make sure the pump they installed is pumping as it should, no vacuum leaks and no pressure leaks.

another problem is those carbs the idle circuit is not jetted for 50:1 mix and it will foul plugs when it is idled for extended periods of time.
at idle the mix was around a 100:1 with the vro and now with mixing it you have too much oil and not enough fuel for a good idle quality.

take it back, make them ride with you,etc.