1976 Evinrude 70 HP running slow

First off let me say I really have no knowledge or marine engines. I bought a boat with a 1976 Evinrude 70HP motor recently and it *supposedly* ran fine but when i took it out i couldn't get it to rev more than 2k RPM. I talked to the mechanic that tuned it up last (few weeks before i bought it) and he said it was running great, ran a dyno ?? prop on it and it was running to spec. I took it back to him and he said it was dropping a cylinder and that one of the coils had gone bad, he replaced it, ran a couple quick tests while i was there, ran it up to 5-6k RPM and it seemed fine. I took it out to the lake here and it still has the same problem. I put the throttle all the way fwd and I can't get it over 2k RPM. It does seem to idle a bit rough, it will run fine at idle speed for a while( 10-15 min) but then die and has a hard time restarting. When you have it in neutral and choke it, it will rev up to about 4k RPM. Any info would be helpful!

Re: 1976 Evinrude 70 HP running slow

I had a similar issue with my Johnson 140. Carbs were good, jets were clean, but it either died when I put it in gear, or if I got it into gear and was able to get RPM's up, it wouldn't plane out or run very well.

I found that I had two problems.

1. The vent hose on my gas tank had gotten some gas in it, and there was a dip in the line, so the gas never left the line. There was enough room for the air to flow into the tank to allow enough gas to move through the system at idle, but when I throttled up, there wasn't enough air space to let gas flow, so the engine would never go wide open. Since my boat wouldn't go fast enough to plane out, I was nose high in the water, which just kept making the venting issue of the tank worse. I would suggest checking to make sure your gas tank is venting.

2. The second issue that I had was that I must have gotten some bad gas. I had replaced by fuel filter at the beginning of the season, but I decided to pull it again and found that there was water in the filter. I replaced the filter and put a fuel / water separater on the system so I can drain it. I had to drain it three times last trip within the first 30 minutes, but now it seems to be okay.

I was telling some of the local guys about this, and one of our boat mechanic buddies told me something I had never heard before about the primer bulb. He said that most people install the primer bulb between the gas tank and the fuel / water separator & filter. All of us talking agreed that we all had our boats setup that way. He suggested that we change it up so that we go from the fuel tank, to the fuel / water separator & filter, then to the bulb, then to the motor. He told us that the pressure from the bulb has a tendency to push bad fuel, water, sediment, etc past the filter and has potential to get it to the carb, resulting in fouled jets. I don't know if this is really "best practice", but it makes sense to me and I plan on making that change this weekend. I do have to note that I live in Bethel, Alaska so we do have a tendency to get water in our fuel from condensation on occasion.

Hope this helps. Let us know if you figure out what the problem is.

Spencer

Re: 1976 Evinrude 70 HP running slow

Do these motors need a fuel filter? Mine doesn't have one. I did replace the fuel line, bulb and all. Should the bulb always be hard owhen it's running or should I be able to squeeze it.

I took it out tonight to run it a little and it still was doing that same thing but after a while it just started working, revved up, much smoother at idle, didn't stall half the time when i put it in gear, ran it up to 4-5k RPM no problem. Then it just quit and was back to being slow. I ran it around a bit and then revved it up with the choke for a bit and it started working and didn't quit. I have no idea what to think of this. Maybe just a bad wiring connection somewhere or could the "brain" be flakey?