1987 Johnson 40 hp fuel issues?

[jartgo]

I've recently purchased a Johnson 40 VRO with electric start, trim & tilt, and remote steering. I've run the boat twice now. The first time I ran it was with a full tank of fuel that came with the boat. Yesterday I had to refuel. I added 10 ounces of oil (that also came with the boat) to 4 gallons of fuel (50:1). When I ran the boat it ran fine for a little while then at full throttle started revving down then right back up, then down, then up, etc. I suspect it has something to do with me filling the tank yesterday, since it ran fine for several hours before I added fuel.

I'm not very familiar with outboard motors but I'm suspecting one of two things (mostly because I don't know what else it would be). My suspicions are that when I filled the tank, some debris got stirred up and there is a restriction in the line or fuel filter?? Or, (after reading on here this evening) it could be a problem with the vent on the gas tank. I'll play with the gas tank next time I get a chance to take it out. Any other suggestions or possible issues? Am I on the right track?

[HighTrim]

So did the previous owner disconnect the VRO system?

[jartgo]

I'm not sure if the VRO is connected. I'm not even really sure what that is. I've just placed an order for a manual. How can I tell if the VRO has been disconnected?

[tashasdaddy]

do you have a fuel line and an oil line going to the motor? an oil tank in the back of the boat?

[jartgo]

No, just the fuel line and a portable fuel tank. Any suggestions on the issue I described?

[HighTrim]

If the VRO is not disabled, you should not be premixing at all. Have a read here.

http://continuouswave.com/whaler/reference/VRO.html

[jtexas]

Follow the fuel line from where it enters the cowling to the fuel pump. if there's a hose leading from the fuel pump to an oil reservoir, then you have VRO and don't need to premix.

If there's an obstruction in the tank, the primer bulb will get sucked flat - if you squeeze it while the engines acting up, it won't open back up again (at least not right away). Similarly, if squeezing the bulb makes the engine run right, that suggests the fuel pump is getting weak.

One question: the fuel tank has a vent somewhere on top, usually it's a thumb screw on the lid...do you have the vent open, or closed?

[jartgo]

The VRO system has been disabled. The vent on the portable tank is open.