Anyone want to help me diagnose a problem I’m having with my outboard?
It’s a 1988 Evinrude 70hp. It has the VRO pump, but the oil side has been disabled and I mix the gas. It was recently rebuilt, including a new crankshaft. I recently finished the break-in period, during which these same problems occurred.
Keep in mind that I’m mechanically inclined, but I’m no mechanic…
The engine starts and runs great. In fact, performance is great overall for the first 10-15 minutes of running. Once the engine get thoroughly warmed up, the following happens:
1) After I shut the engine down I’ll go to re-start it. If I don’t get it started right away (like I usually do) it will crank and crank without firing. A little starting fluid in the air box gets it going immediately, but it will sputter as though its struggling to get gas at first. My theory is that after the cyliders burn the gas in the carb (or maybe the gas that is close to the carb in the line) that is sitting there from running prior, there is no more gas being delivered until the engine is running again. Related might be the fact that when I squeeze the bulb on the fuel line when the engine is not running, it will get so hard that I can’t squeeze it at all. It’s like there is something blocking the fuel from moving at all (again, whent the engine isn’t running).
2) When I’m running at mid-high RPMs after a while (10-15 minutes) the engine will eventually start dogging like it isn’t getting gas, is getting too much gas, or … I don’t know. The problem starts like this: I’ll be moving at 3/4+ throttle, and the boat will suddenly and briefly lurch down to a fast idle rpm. At first, it will do this sporatically and very briefly. But if I keep going, it will occur more regularly and the slow downs will last longer. Eventually, I’ll be stuck at a fast idle speed no matter how far down I put the throttle. It will just dog along. If I keep moving at the fast idle speed, it will finally just stop running all together. Once the engine cools down again, I’m good to go (though that takes a long time). If I don’t run the engine more than 5-10 minutes the problem doesn’t occur at all. It also seems to help if I keep my running speed down to 1/2-3/4 throttle, or at least it takes longer for this problem to start when I do that.
I was thinking at first that there might be a problem with the fuel pump, but why would it be temperature related? Then I started thinking about the choke/primer system. When I push the key in (this is a console boat) to activate the primer the engine will get doggy when problem #2 isn’t occurring. But if I push the key in while the engine is having problem #2 (during the time that the engine is dogging on its own) there is no change.
I have been using the boat, and provided I get it started right away and don’t make long runs I have no problem. But I can’t operate like this forever…
I’ll probably have to bring the engine back to the guy that rebuilt it to see what he can do, but I thought I’d check here first. Note that I did run 25:1 gas in the engine during break in. These same problems occurred at that time. I did change the spark plugs following the break-in period and there has been no change in performance (other than the typical smoother idle and less smoke). I am now running sea foam in the gas despite my conerns about doing that so soon after the break-in proceedure. I probably have 10 gallons mixed with sea-foam through the motor since I completed the break-in.
Any thoughts? THANKS!!! 
