1976 Evinrude 85hp loses power, backfires, dies

[Westgunn]

Been pouring through information here looking for similar problems and fixes. Some seem close to what I'm experiencing so I think I have some places to start, but wanted to run my situation by you guys just in case something else could be the problem with my evinrude.

I transplanted this motor to the back of a project pontoon (done by a mechanic). Put it on muffs and had to run some starting fluid to get it going in the driveway (fresh fuel, marine grade oil 50:1). Seemed to run well, so I took it to the lake for a test spin. The motor seemed to start easier in the water which was promising. I had to make some adjustments to the shift cable, as it was not properly connected in the throttle control box at the helm, but after it seemed to shift in F-N-R just fine.

Gave it some gas and got up on plane. It ran great for about 3 minutes and I got it close to WOT, but then lost power down to about idle. I didn't let off the gas, and after a minute or so it took off again. Less than a minute later it lossed power again down to about idle so I put it in neutral. At that point, it idled really high and kind of rough. Almost sounds like a back fire. I adjusted the throttle down at idle, and the next time it "back fired" it killed the engine at the lower idle RPM's. Restarted it with no problem though, but the problem continued.

Brought it home and added a "pee hole" just to make sure water is running through the water jacket properly. Ran sea foam through the carbs to clean out junk and replaced all spark plugs. I moved over the automatic choke heat sensor wire to primary to bypass a possibly faulty sensor. Ran pretty well in the drive way, but I can still hear a miss or back fire even after new plugs, and it would occasionally die if the "misfire" was a bad one...for lack of better terms.

I'm guessing my next move is to replace the power pack, but I really don't know how to verify that. Or the rectifiers?? Or is this possibly a bigger problem than that? Any help is greatly appreciated!! Please forgive my lack of mechanical vocabulary...you guys must have the patience of Job!

Thanks in advance!

 

[Daviet]

Re: 1976 Evinrude 85hp loses power, backfires, dies

Have you removed the carbs and cleaned them, paying attention to the high speed orifices?
Sounds like you have some plugged or restricted.
Have you checked the spark, or done a cylinder drop test to see if you have good spark on all cylinders?
It doesn't sound like a compression problem by the way you described it, but you might want to run a compression test to get a baseline of the health of the engine.

 

[Westgunn]

Re: 1976 Evinrude 85hp loses power, backfires, dies

Have you removed the carbs and cleaned them, paying attention to the high speed orifices?
Sounds like you have some plugged or restricted.
Have you checked the spark, or done a cylinder drop test to see if you have good spark on all cylinders?
It doesn't sound like a compression problem by the way you described it, but you might want to run a compression test to get a baseline of the health of the engine.

No, I haven't done those things, but I'll start with them. I just don't know how right off. I guess I'll run some searches on YouTube to see if I can find a few tutorials before purchasing unneeded parts. Thank you for the advice!

 

[Westgunn]

Re: 1976 Evinrude 85hp loses power, backfires, dies

I pulled the intake cover off the carbs and this time noticed the gasket it around is in terrible shape. The bottom of the gasket is completely broken off. Could this be a part of this problem? I'm definitely going to replace it as soon as I can...just wondering if some kind of air leak could affect how it runs? Can't help but notice there is no air filter on this motor at all.

 

[joe agey]

Re: 1976 Evinrude 85hp loses power, backfires, dies

I have a evinrude 150 that had the same problem it would take off fine and all of a sudden lost power make a long story short if you take the check valve and spray some carburetor cleaner in them one of them could be stuck and that should fix the problem that was the problem with my boat after cleaning the check valve the boat ran great.


Joe

 

[Daviet]

Re: 1976 Evinrude 85hp loses power, backfires, dies

Don't worry about the gasket, it's not causing your problem. Go ahead and install a new one when you reassemble the air box.
I don't think your engine has the checkvalve that joe is talking about.
Check compression and spark and then move on to the carbs.

 

[Westgunn]

Re: 1976 Evinrude 85hp loses power, backfires, dies

Don't worry about the gasket, it's not causing your problem. Go ahead and install a new one when you reassemble the air box.
I don't think your engine has the checkvalve that joe is talking about.
Check compression and spark and then move on to the carbs.

I've got to buy a compression and spark tester tomorrow, then I'll make these checks. In the meantime, I found an evinrude that's doing exactly what mine is on youtube.

1974 Evinrude 115 runs poorly and misfires - YouTube

 

[Westgunn]

Re: 1976 Evinrude 85hp loses power, backfires, dies

Finally made above checks.

Got spark on all 4 wires.

Compression:
Cylinder 1: 115
Cylinder 2: 117
Cylinder 3: 115
Cylinder 4: 114

Guess I'm back to carburetor.

 

[Daviet]

Re: 1976 Evinrude 85hp loses power, backfires, dies

Compression looks good, time for carb work.

 

[emdsapmgr]

Re: 1976 Evinrude 85hp loses power, backfires, dies

You may have multiple problems. 1. Possible that your fuel pump is weak, causing it to run out of fuel at higher throttle. Have a buddy constantly prime the fuel hose bulb-it will force extra fuel into the carbs. If it runs fine as long as you constantly prime the fuel hose bulb, you've got a fuel restriction or weak pump. 2. The backfiring could indicated that the link arm has become detached between the spark advance lever and the timer base. When that happens, the timing will be way off. The relationship between the throttle position and the spark advance must be in sync or it will not run right at all. An easy thing to check and repair. The compression is good.

 

[Westgunn]

Re: 1976 Evinrude 85hp loses power, backfires, dies

Thanks for the replies. I won't have it on the water again until Monday probably, so I won't have it under load till then. But I'll pump the prime bulb and see what happens. Don't know how to check the link arm you mentioned emd....I'll go through the info here and see if youtube has anything. In the meantime, I shot a vid of my motor on muffs:

1976 Evinrude 85 hp - YouTube

Really misses bad at 0:54 and 2:00-2:19.

Wife's been complaining about how much time I've spent on it lately, so it's going to be slow going. I've been reluctant to dive into the carbs as of yet, so I'm going to run a can of sea foam in fresh fuel first. I don't deal with carbs often, so I won't be as proficient as guys with experience with them.

 

[James R]

Re: 1976 Evinrude 85hp loses power, backfires, dies

From the compressions you have a good motor. Don't ruin it by neglect. Remove the carbs, strip clean and rebuild with new kits.
If a carb is even partially blocked you will burn a piston and cylinder out. This is a 2 stroke and needs the correct fuel flow to get the lubrication. The starting and slowing does sound like a fuel pump. The squeezing of the primer bulb when the motor slows will usually show if the pump is weak.

 

[emdsapmgr]

Re: 1976 Evinrude 85hp loses power, backfires, dies

I saw two things in the video. An occasional miss at idle. That's typically a "lean sneeze". Likely a lean condition caused by a possible restriction in the small idle passages of the carbs. If you remove the carbs and clean the passages with a product like Gumout, it should clear up the occasional idle miss. I also noted a pickup of rpm's for an instant at higher rpm's. I'd guess the engine may be running on only 3 cyls, but occasionally the 4th cyl will kick in. An ignition problem probably. You need to determine which cyls are firing all the time and if one is not-which one. A power pack or stator, perhaps. Once you get these issues resolved, it should be a good runner-from the way it sounds in the video.

 

[James R]

Re: 1976 Evinrude 85hp loses power, backfires, dies

Emdsapmgr is right about the possibility of a cylinder dropping. You can use a timing light to monitor the sparks on each cylinder in turn. Could just be a bad plug wire or plug.

 

[keefallan]

Re: 1976 Evinrude 85hp loses power, backfires, dies

If you have an ohmmeter, you can check the resistances of the coils. I know that the plug wires are attached to the coil itself(unlike the newer style), but you can compare the numbers of all 4. They should all be in the same relative range. You can read between the secondary side(spark plug wire) and the primary side(orange wire?). The coil is a transformer that steps up the 12v in the primary to 25,000v on the secondary. It's all in ratios. That's why your coils should all have the same relative readings. These readings may also give an indication of a weak coil. Another old trick is run it at night in the dark(so you can keep everyone awake!!LOL!). If there is any bad insulation on the wires, it will glow in the dark! You'll see the spark.

 

[Westgunn]

Re: 1976 Evinrude 85hp loses power, backfires, dies

Unfortunately my plans for getting the boat on the water the last week have all fallen through. Hopefully Saturday. But I was reading through the secret files looking for the information I need to continue to troubleshoot and finally read one of them that at first didn't seem to be very relevant...the pressure vs non-pressure tanks.

The original motor for this boat was a Suzuki. I'm guessing a 2001 model 50 hp 2 stroke...haven't yet confirmed that. But I believe I'm running a non-pressure tank to my Evinrude right now. Seems a likely culprit as to why I may have low fuel flow and experience the dying out close to WOT. What do you guys think? Is there a way to modify a non-pressure tank and make it a pressure tank. I mean, I'm sure there is, just wondering if its been done before by any of you guys? Maybe just cap off a vent line on the tank with Great Stuff or something along those lines?

 

[Westgunn]

Re: 1976 Evinrude 85hp loses power, backfires, dies

Just as a side note, I will be running all the checks suggested here when time permits for me. My plan for payday is to replace damn near everything. This motor is older than I am, and I think it's still running all original equipment on the motor aside from a starter solenoid which I replaced a couple months back (which is pretty amazing to be honest). So the following upgrades will be made in the near future:

New ignition coil
New power pack
Dual carb kits
New fuel pump
New condensor
New rectifier
New impeller
New fuel hose lines

Considering the importance of a solid reliable motor on the water, these things in my opinion should all be done anyhow. Just gonna be slow going as I have zero experience with this. Pretty sure a mechanic would charge me north of $2 grand to do this stuff, but I can get all the parts for under $250 and just learn to do it myself. I like the idea of being intimately familiar with the motor on the boat my family and I will be out on!

Thanks again guys for all your input!! Couldn't do this without y'all!