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Not all cylinders working

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BenRW

New member
I have a 1986 70hp Evinrude outboard. It has been struggling for a while in the 2000-3000 rpm range, and recently I seem to have lost some cylinders. Here is what I have done:

- Checked spark with spark tester and all cylinders have spark
- Removed spark plug wires 1 at a time. Only the middle cylinder seems to have any effect. The bottom one definitely doesn't. I couldn't quite tell with the top.
- Tested compression: 145, 139, 135. Seems good.
- Checked ignition coil and sensor with ohmeter as much as I could without specialized equipment.
- Confirmed that there is no gooey stuff dripping down from stator.
- Tested resistance of spark plug wires. All are good.
- Replaced and gapped all spark plugs.
- Rebuilt all 3 carburetors.
- Replaced fuel pump, fuel separator, fuel filter, parts of fuel line.

Engine runs, but clearly not on all cylinders, and requires a lot of choke. Any ideas what could be the problem?
 
Reed valves checked ?--------Bottom crank seal could be an issue.---------Does spark jump a gap of 3/8", yes or no ?
 
Compression is good and spark is good put a little fuel mix directly into the bottom cylinder and just connect that plug wire and see if it fires on the bottom cylinder only. If it fires good then you have fuel delivery issues. When you rebuilt the carbs did you pull the welsh plugs and jets and soak them good in carb cleaner. I use high pressure water to scour the circuits and blow dry with air. Surface the flanges on a glass table with 220 grit and just pull the carb in one direction only until it all shines the same. Run a soft copper wire through the jets so you dont ream them any larger. If your sure the carbs are good and your still not running on the bottom or top cyl you either have reed issues or crank seal issues.
 
I'm still struggling with this issue. Since my last post, I completely dismantled and reassembled the crankcase and head. Everything internally looked really nice. The reeds were in perfect shape, and since I resealed the crankcase, I don't think a crank seal could be the issue. I did find and fix a bad thermostat, which turns out to have been stuck open for the last year. I went out today and after running for 10 minutes I was not able to go over 3000 rpm. The engine loses power when I try to exceed 3000.

- I tested the cylinders again. There is good spark on all cylinders, but there is no effect when I remove the top spark plug.
- I also noticed that fuel is spitting out of the mouth of the top cylinder carburetor.
- I removed the top carburetor again and took it apart. It looks perfect. All holes are clean and open. The float is level. The needle valve looks clean and new. All jets are clean.

My next step is to sand the flange with 200 grit as kimcrbrw1 suggested. Any other ideas?
 
Mark the flywheel for TDC for each cylinder.--------------Then use a timing light to see where each one fires.--------------What colour is the orange wire going to each coil ?
 
Thanks for all the replies.
-The reeds really look like they are in perfect condition. Nice spring in all.
-Yes. I did replace all gaskets. The only thing I didn't replace was the upper bearing O-ring(0313754). I wonder if that is an issue.
-I will try the timing light idea - need to find a timing light to borrow.
-The orange wires to the coils are brownish-orange with a blue stripe. The middle coil doesn't seem to have a stripe.
 
Here is the latest status on this engine:

-Yes. The wires to the coils are orange-blue on top and orange-green on bottom.
-I haven't found a timing light, so I still haven't done the timing test.
-However, I did replace the top coil with a new one.
On Monday I took the boat out. It was still sluggish for the first 5 minutes, but then all of a sudden it started working fine. Full power control up to 5500 rpm. There was no sluggishness in the 2000-3000 rpm range that I had felt all summer, and it seemed like all cylinders were working. I tested it for about 45 minutes and never had any more issues.

So, I want to think that the new coil fixed the problem. But, what could explain the sluggishness for the first 5 minutes? I have checked and double checked the fuel lines so many times that I don't think there could have been a constraint there. Can I trust the engine to be dependable now?
 
Maybe some carbon burned off, A electrical connection on a coil or plug wire finally seated properly,ground wire? who knows!! must be one of the last things you adjusted or meddled with.
 
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