No fire on top or bottom cylinder, sometimes..

Hello everyone, back again to ask for some advice on dealing with my cranky Evinrude 70 (84). The first issue was when first started there would be a lag before all the cylinders starting firing. It seemed like an electrical issue because it would just snap and start running fine. After going through every electrical connection, from the battery back that issue seems to have been resolved. But now it will randomly drop the top or bottom cylinders off. If I cover the mouth of the bottom cylinder carb it doesn't affect the engine, cover all the others and it dies. Now the odd part is that sometimes the bottom carb will not respond or sometimes the top one wont respond, never had any issues with the middle cylinder. I have had an inline spark tester on the cylinders when they die out and still have spark. Compression is 120-130 on all cylinders and the carbs have been meticulously rebuilt. The coils have been swapped around too with no change. Another interesting thing is when the dead cylinder picks back up there will be alot of smoke, indicating to me anyway that there was oil and fuel in the cylinder. Im not really sure where to go from here in my diagnosis of the problem, or if there even is a problem and this is just the nature of the 2 stroke 30 year old beast.

One thing for sure, it isn't the nature of the beast. It should run well. Make sure water is not getting into the cylinders (warped exhaust cover baffle plate).

Now that you mention it I have noticed salt residue on the exhaust plate around the gaskets. Unfortunately I have dealt with the removal of one of these exhaust plates before and I broke all but 2 bolts off in the block and had to trash the whole thing. Many people including an evinrude mechanic have told me that it is impossible/not worth it to remove the old style three piece exhaust plate, I suppose this is the end for this engine then.

I keep 'em going.....be carefull with your removal, use "blaster" or another high quality penetrant.......don't rush the job, a little heat.....aluminum expands under heat more than steel, helping to loosen with a lite impact. Flush seawater run motors religiously. Pilot hole drill broken bolts/screws with a tiny high quality bit, then bring up your size and if your pilot is centered, then your in good shape. Don't mess up your pilot hole......STAY CENTERED!

Perform stator test under both cold and hot motor temp......this is a good suspect. Modules are nasty and trouble makers too! Mercurys call them a "switch box" .......'cause when all else fails, the last thing to do is "switch it out". Good luck, brother!

Went out and got a new multimeter today and tested some electrical components, all of them came out within spec except for the sensor coil/timer base. Manual says it should be 17 +- 5 ohm. I got 13 on one point and 30-29 on the other two points. Manual doesn't specify what will happen if these are out of spec it just says replace component.

As for leaking exhaust plates I ran it to double check and a tiny amount of water is seeping through when the engine is cold, I would really like to avoid replacing the gasket if possible. The other engine I had trouble with removing the bolts hasn't been thrown out completely; I still work on removing the bolts for practice. Not much luck yet but I feel my skill is the problem there. Before attempting to remove the bolts the first time I soaked them in Pb blaster for close to 3 months and used heat and every time I thought they were breaking loose but after two turns or so I would hear a snap. It tricked me with every bolt too, thought it was coming loose then snap.

All my engines and boats are washed thoroughly with fresh water after running, engines are flushed for a good 15 minutes and boats are washed to the point of sinking. I really hate salt corrosion.

I think I have figured out why the bottom cylinder wont fire, it has a very weak spark. A spark shows up in the inline spark tester no problem but when a spark plug was used to test there was no spark on that cylinder, its not strong enough to jump the gap. The coils have been swapped around and the problem doesn't follow so its not coils but other than that I am clueless. I just so happen to have a spare stator and timing base but when tested they show no resistance, I think I will take the gamble though and swap them anyway cause new stators and timing bases are pretty expensive.

Try this on one of your practice bolts for the exhaust plate. Put a wrench on the bolt, pull about 10 lbs. torque, and tap on the head of the bolt with a light hammer. or put a socket on it and pull the torque while tapping side of socket.
This seems to have worked best for me. I tried heat, much soaking with many penetrants, using a wrench and tapping on the unused end of it.
Broke three bolts before finding this way.

Thanks, I will have to try that out. But now I still have to deal with an engine that breaks the rules of engines. Good compression, good properly timed spark, and good fuel delivery but somehow it will not fire.

Spark in line test,but no spark at plug. You switched coils, no change. Try using a new plug.

Not really sure what happened to my post, there were some technical difficulties. But before getting locked out of my account and losing half my post I meant to say that the stator was replaced and that fixed the spark issue, the old stator was a melted mess. But even after that I was still having issues until going back the root of my problem. It wasn't so much that the cylinder wasn't firing it was that it would not choke out like the middle cylinder. And whats different between the top and bottom cylinder and the middle cylinder. The butterflys are adjustable on the top and bottom, so I cracked open the butterfly on the top and bottom and tah-dah they choke out just like the middle cylinder. The engine runs much smoother now at idle and at speed. All this because I forgot the sync part of lync and sync... :rolleyes: Thanks everyone for helping out, I wouldn't have discovered my melted stator until I needed tow boat.