HELP!! 77 Evinrude 70hp misfire

[BassmanTy]

I have a 77 evinrude 70hp that misfires. Mixed 50:1, new plugs, new fuel, and carbs professionally rebuilt and vacuum tested after. It will miss real bad, and ill have to run it at full or close to full acceleration for about 15 min straight before it will clear up. Seems to be getting too much fuel. Any help would be greatly appreciated. Would like to go on a fishing trip in 2 weeks, but I need this thing fixed, and can't afford to take it in.

 

[oldboat1]

Shops typically work with their own fuel to rule out using owner's contaminated tank. When you added fresh fuel, did you add it to a fresh, empty tank? If not you are burning contaminated fuel. The likeliest culprit is water. Draw some fuel out of the tank you use and let it settle out in a glass jar. Any water will appear at the bottom of the jar.

 

[racerone]

Run with a timing light.-----One cylinder at a time to see how spark behaves.----Post your compression test numbers to keep for reference.----How did it run for you last season ?

 

[BassmanTy]

Shops typically work with their own fuel to rule out using owner's contaminated tank. When you added fresh fuel, did you add it to a fresh, empty tank? If not you are burning contaminated fuel. The likeliest culprit is water. Draw some fuel out of the tank you use and let it settle out in a glass jar. Any water will appear at the bottom

Run with a timing light.-----One cylinder at a time to see how spark behaves.----Post your compression test numbers to keep for reference.----How did it run for you last season ?

Run with a timing light.-----One cylinder at a time to see how spark behaves.----Post your compression test numbers to keep for reference.----How did it run for you last season ?

I know it's not water in fuel, checked that. Compression is 100 psi in all 3 cylinders. Ill check with a timing light, but I'm almost positive it's getting too much fuel. Unsure how to adjust that. I added an inline filter too, but no help. Last year it ran rough too, but not nearly as bad

 

[racerone]

Some will argue but compression should be around 140 PSI on that motor.-----Perhaps check fuel pump diaphragm.-----If ruptured , a new diaphragm is not expensive.----No mixture adjustment on those other than changing the jets.

 

[BassmanTy]

Diaphragm has been replaced as well. Before I bought it. If the Diaphragm was bad, wouldn't it not get enough fuel? If I tap the choke with the engine running, it dies. The air box is pretty wet, I haven't pulled it off and ran it to see which carb yet.

 

[racerone]

Well---I can rebuild your motor top and bottom without glancing at a manual.----What else have you done and what work are you prepared to do ????

 

[BassmanTy]

Well I can't really afford to rebuild it. I've had carbs rebuilt professionally, put new plugs in, then replaced again with lower resistance plugs, added an inline filter, cleaned the fuel tank and replaced fuel.

 

[racerone]

I am just saying that I am very , very familiar with that motor !!

 

[oldboat1]

In two weeks you could swap out the head gasket and refinish the head mating surface. That might increase compression and/or improve running. Did the motor overheat at any point? Running with a timing light to see if you are dropping a cylinder, as suggested, is also something you can do without a lot of fuss. You may want a driver to help out.

Make sure the choke is not sticking partially closed (correction).

Run with a portable tank with fresh mix -- use that on the fishing trip, if that is a temporary solution. It's probably not a good time to experiment with plugs -- maybe go back to oem and gap to specs (.030, .035 or .040, potentially).

Replace the 20amp fuse with a fresh one, and clean the connectors.

 

[BassmanTy]

I am just saying that I am very , very familiar with that motor !!

I don't disagree, I'm not familiar with boat motors at all. My question about the diaphragm was a serious question too.

 

[oldboat1]

seems like you might be fixed on a flooding problem -- but that may be a result of no spark (or spark that is too weak).

 

[BassmanTy]

seems like you might be fixed on a flooding problem -- but that may be a result of no spark (or spark that is too weak).

Definitely a carb problem. I do think there might be 2 weaker coils, but Definitely getting spark. I filled up the 3 fuel lines to the carbs with carb cleaner, ran it, and then opened up the bowl and flushed them out. Seems to have made a difference. I'm gonna take her out Thursday and see what happens. My boat mechanic is gonna meet me out there too. Thank you all for your help. Id have brought to him sooner, but I moved 2 hrs away, and don't have much money for a mechanic right now. But he's willing to look for free.

 

[oldboat1]

A few folks out here screaming OIL, I think. Hope the motor and the trip are both successful.