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1978 Evinrude 70HP woes

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billythegrape

Contributing Member
Hi, here from Knoxville, TN.


I am at a loss and need help. I have a 24' pontoon boat. I had a 50hp johnson on there that worked perfectly. However, it was a short shaft and kept coming out of the water, so I decided to see if someone would trade for a long shaft. I got the 78 as an equal trade; tested compression and it was good so I took it home and put it on.


The engine ran like a top. It felt like it was twice as fast and we got to the island we go to in Norris Lake in record time. On the way back it started acting up, lost tons of power and was generally running like crap. I had noticed that the stator and rectifier showed signs of melting, so when I got home I ordered them.


Put the new stator and rectifier on and then set timing (WOT, all plugs out, spark tester and timing light lead on cyl 1) to 15 deg as this was 2 deg less than 17. Decided to rebuild the carbs and change all the fuel lines and pump; got that done, carbs were very clean, but had old gaskets. Tried it on the muffs, it was hard to start but got going and was ok, so I brought it to the lake. It ran badly with no power and died at the ramp. Pulled the plugs, found water on them.


Pulled the head, it was very corroded, but the cylinders looked good and the head and water jacket were straight. Replaced the head gasket, water jacket gasket, melted pressure relief valves and grommets, and the thermostat and associated gaskets. Cleaned everything. Boat ran ok on the muffs, so I brought it down to the lake and it died on the ramp. Got it going and pulled plug wires; #3 cyl was not contributing so I figured the coil was dead. It was melted.


Replaced all the coils and decided to do the exhaust manifold gaskets as well because I read that those should be changed at some point; since the head was so nasty I figured it must be to. It was. Cleaned everything on it, replaced all gaskets. Took it to the lake today. It fired right up, but had no power. Drove it for a bit, pulled the cover off the carbs, saw that the chokes were all shut. Adjusted the chokes to their proper positions, it ran better with more power but still not fabulously.


I am at a loss. What else can I check? The plug wires? I messed with them while going around on the boat and they shocked the crap out of me; they don't seem like they fit super well into the coils. The engine feels like it is being held back by something. Compression is still fine at 120-120-115. HELP!!
 
The heads all warp to a degree and must be resurfaced.----Yes all heads are warped !---Perhaps the high speed jets ( orifice plugs ) are plugged.----They are in the bottom of float bowl.
 
The heads were perfectly straight, as measured with a straight edge. As was the water jacket and block. I sanded with 2000 grit and rechecked, no change. The jets were all cleaned during the carb rebuild, but were perfectly clean anyway.
 
I wish I thought that.

Today's diagnostic session was weird. I wanted to set the timing back to where it was initially but when I had the light hooked to cyl 1 I couldn't see the timing marks while cranking. When I found them, they were 90 degrees away!

I figured it might be getting cross voltage with the second wire, so I moved it completely away from the second coil. Same thing. I disconnected and reconnected it, then was disappointed to see that I could not get my spark tester or a plug to fire on the #1 cyl. When I tried to check for 12V at the power pack on the orange lead while cranking, it shocked me. The other coils fired just fine.

After fiddling for a bit, it started working again. I set the timing back to 13 deg, and put new ends on the spark plug wires where they connect to the plugs. It ran great on the muffs. Took to the lake, it wouldn't even start. Pulled it back out, looked it over, put it back in, it started up and ran, but no power.

Now I am wondering about two things. Could the timing base be messed up somehow? Or are the reeds messed up? It was blowing a lot of fuel out of the exhaust at the lake.
 
1. Did you recheck for water in the cylinders after your repair? With all the melted stuff you report, it is hard to believe those exhaust plates are not warped.
 
Did you recheck for water in the cylinders after your repair? With all the melted stuff you report, it is hard to believe those exhaust plates are not warped.

Yes. The only melted stuff was the two pressure relief valves. Honestly I could melt those with a strong fart, so I don't think the over heat was all that bad. I also don't know why heads and manifolds being perfectly straight as checked with a straight edge is that hard to believe.
 
Going to check the reeds when I get the chance, and going to pull the flywheel and look at the timing base. I am missing something simple here, I just know it.
 
billythegrape said:
Did you recheck for water in the cylinders after your repair? With all the melted stuff you report, it is hard to believe those exhaust plates are not warped.

Yes. The only melted stuff was the two pressure relief valves. Honestly I could melt those with a strong fart, so I don't think the over heat was all that bad. I also don't know why heads and manifolds being perfectly straight as checked with a straight edge is that hard to believe.
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Just trying to help. I've never seen an overheated 3-cyl that didn't have warped exhaust cover plates. The plate is too thin around the exhaust ports and no support on the other side, and will warp with the slightest bit of overheat. and squirt water into the exhaust port. But you are the guy there inspecting it, so whatever you say is ok with me. I'll leave it up to you now.
 

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fdrgator said:
Just trying to help. I've never seen an overheated 3-cyl that didn't have warped exhaust cover plates. The plate is too thin around the exhaust ports and no support on the other side, and will warp with the slightest bit of overheat. and squirt water into the exhaust port. But you are the guy there inspecting it, so whatever you say is ok with me. I'll leave it up to you now.
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Ya, I understand, sorry, not trying to be a dick. It's just I've been a mechanic for close to 20 years now, just on 4 stroke car stuff, so I do know my way around engines. 2 stroke is somewhat of a mystery to me, but I'm getting to know it through books and videos. I definitely appreciate the input, but I did check everything with a straight edge after reading exactly the same thing you had said.
 
The 2 strokes are so simple that many folks can't figure them out.----Sorry too be so blunt to an experienced mechanic.---Good luck with your motor.
 
racerone said:
The 2 strokes are so simple that many folks can't figure them out.----Sorry too be so blunt to an experienced mechanic.---Good luck with your motor.
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Totally fine man, I just wanted to explain that while I'm an idiot, I'm not a COMPLETE idiot.;)
 
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billythegrape said:
Did you recheck for water in the cylinders after your repair? With all the melted stuff you report, it is hard to believe those exhaust plates are not warped.

Yes. The only melted stuff was the two pressure relief valves. Honestly I could melt those with a strong fart, so I don't think the over heat was all that bad. I also don't know why heads and manifolds being perfectly straight as checked with a straight edge is that hard to believe.
Click to expand...
Those pressure relief valves do not melt that easy. If they melted the overheat was bad. Do a cylinder drop test on it.
 
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I think I'm going to replace all of the reeds. Any suggestions or just go with stock? My DVA comes in tomorrow so that I can double check everything else. Wouldn't surprise me if there were multiple problems.
 
Despite amazing wisdom to the contrary, I ordered new reeds. The service manual says an allowance of 0.010" is ok, but I had read elsewhere that if you see light through them they are bad. I figured I was already in there so... I had to order new intake gaskets anyway to replace the ones I took off.






Got a chance to test things with my DVA today. Took a minute to figure out how to make it work, but I got it. The service manual from 1978 says to use a neon test light, but I don't have one of those, so I was able to get a DVA reading for this engine from CDI Electronics. Here're the readings:






Stator- supposed to be 150V-400V, my reading was 295V, well within spec; it's brand new, so not surprising.






Timer base - supposed to be 0.6V+






Sensor 1- 1.54V


Sensor 2- 2.7V


Sensor 3- 2.3V






These readings appear to be in spec. According to the CDI guide, "The trigger signal rides on top of the high voltage on these timer bases. Check stator DVA first. Then if timer base DVA is 0.6 - 2.5 V, the pack is faulty."






This is exactly what I did. Two of the readings fall within this guideline, one does not. I tested three times and got the same results.






It goes on further to say, "Check the DVA voltage on each Black/White wire to engine ground. You should have a reading of at least 150V or more (while connected to the pack). If the reading is low, disconnect the timer base wires from the pack and recheck the Black/White terminals ON THE PACK. If the voltage jumps up to an acceptable reading, the timer base may have a problem in the internal wiring (possibly a thin spot in the insulation on one wire)."






I did this, and got approximately 0.9V on each wire when connected. Then I disconnected them and got pretty much the same thing. This would lead me to believe that the timer base is ok, and that the power pack is dead or on its way.






Thoughts?
 
Called CDI, they said to DVA the coil wires out of the power pack. If below 150V, replace the power pack. They had nothing, so I guess it's the power pack.
 
Ok an update. Here's what I've done.



Replaced the power pack. There was 0v from the power pack to the coils using a DVA. Now the boat fires right up, practically the first turn of the key. Replaced the spark plugs. They were NGK, got the proper champions in there and correctly gapped. Now everything tests ok.



Took the boat out, it really wants to go, but acts like it's starving for fuel.



Replaced the clapped out fuel tank and replaced the lines, primer bulb, and the fittings. Wentout again, boat went along ok, but after a but suffered a lot of sputtering and stuff at WOT, pumping with the primer bulb didn't seem to make a difference. Plugs are not fouled, but there did seem to be some smoke and gas in the water.



Replaced lines on carbs with new stuff. Tested fuel pump.



With output hose off, fuel comes out, but it's pretty weak. Like a little stream at the bottom of the hose. Pulse nipple has strong pulses. Put my snap on fuel gauge teed into output, pressure is very low. The gauge measures in 2 4 6 8 graduations; it barely makes it above 2.



I'm thinking the fuel pump is bad. Yes, I replaced it previously, but I was an idiot and cheaped out on it with a 20 dollar one from amazon. Any thoughts?
 
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