1981 Evinrude 115hp. Throttle posessed!!??

[fsujack21]

I have a 1981 Evinrude v4 115hp. I bought this boat last year and I did a LOT of maintenance this offseason to the engine. I installed new head gaskets, new thermostats, waterpump, spark plugs, wires, I rebuilt the carbs, replaced all fuel lines, and did a decarb treatment. I have used it about 10 times this year and it has been running terrific.
Today after running into a strong head wind and choppy seas the rpms dropped, almost as if it went into SLOW mode. I checked the tell tale and the water was still cool. I backed the throttle down then advanced it again and she ran normally. Later on in the trip it the rmps started doing the same thing. I kept the thottle in a fixed position and the rmps would drop down then bounce back up this kept happening again and again. It felt as if someone else was controlling my throttle and messing with me.
As this is an old engine I'm hoping to not have to dump much more money into her, but I can't afford a repower for another year or 2 so I was looking to nurse this one along.
Anyone have an idea where to start? MY first guess was a bad fuel pump. My other guess was a bad power pack?? How do I diagnose this?

Thanks
Jim

 

[eclark53520]

Re: 1981 Evinrude 115hp. Throttle posessed!!??

You can diagnose a bad fuel pump pretty easily. Just pump the fuel bulb a few times while it's acting up. If the motor picks up after pumping the bulb, it's probably the fuel pump.

If it's not that, then start looking into something intermittent on the ignition side of things.

 

[fsujack21]

Re: 1981 Evinrude 115hp. Throttle posessed!!??

I can't get down to the boat for a few days to test that, but to be more specific the rpms were literally bouncing from 4200-1200 and back and forth. then it would be fine at 4200 for a few minutes. could a bad fuel pump even cause these symptoms or is it more likely something electrical?

 

[emdsapmgr]

Re: 1981 Evinrude 115hp. Throttle posessed!!??

That engine has two power packs. One for each head. Possible one of them is going bad. Check your spark after the engine is warmed up. You can swap those matching power packs for testing purposes. Weak ignition components tend to fail when the engine heats up to normal operating temps. (It may run fine when cold-then crap out when fully warmed up.)

 

[ryguy1101]

Re: 1981 Evinrude 115hp. Throttle posessed!!??

symptoms sound like water in the fuel to me. Mimics exactly what i've experienced assuming you do have an in line fuel/water separator. if not, disregard.

 

[fsujack21]

Re: 1981 Evinrude 115hp. Throttle posessed!!??

I have a water separator with only about 20hrs on it, fresh fuel brought in on cans from a station on land and i always add stabil and startron so I don't think water in the fuel is the issue.

As far as identifying the powerpacks is there a test with an ohm meter or anything like that to find out if they are the culprit or is swapping them out the only way to test? Also, is there a chance that its the coils and not the powerpack? how can I tell?

Thanks again!

 

[emdsapmgr]

Re: 1981 Evinrude 115hp. Throttle posessed!!??

Use an inductive timing light to check the spark on each plugwire. The flashes in the gun will tell you about the quality of the spark on each wire. If you have weak spark on one wire, you can swap that coil with any other coil to see if the problem moves, just like with the power packs. There are diagnosic tools for checking these crossflow ignition systems-at marine dealers. There are some voltage tests which can be run on the stator and timer base. It requires a special "peak reading" voltmeter. Check out the troubleshooting information found on the web at cdielectronics.

 

[fsujack21]

Re: 1981 Evinrude 115hp. Throttle posessed!!??

I think i solved it. I was looking at the engine while at high rmps and I noticed some fuel driping out of the bottom of the upper carb. When I pulled everything apart I discovered a pin hole in the fuel line at the base of the carb. I replaced all the fuel lines in the engine and everything seems to be working fine. There must have been a vaccum leak from the old fuel lines. In the offseason i replaced the fuel lines from the tank to the engine, I didn't think to replace the ones in the engine also. Hopefully this fixes it.

Thanks for all the help

 

[jgriner]

Re: 1981 Evinrude 115hp. Throttle posessed!!??

sounds great