1973 50 hp evinrude (50373r) bogs down past half throttle

[Can'tFishEnough]

Then it started to Rev up and down in 2 second increments and wouldn't steady out. Also there was quite a bit of oil sheen in the water. Took it right back out of the water.

...Also there is a hole in the foot with oil leaking from it.

my 2 cents on this part (based on my limited outboard experience):
I had an outboard do this reving up and down thing and it turned out to be an air leak at the intake manifold and carb gasket. There was just a very slight bit of pitting there. I used a small tire pump to put pressure in a jar with some charcoal burning under a rag soaked in 2 cycle oil. Made a plate for the carb front out of thick plexiglass and put a hole in the center for a rubber hose to get the smoke from the jar (jar lid had 2 holes one for "smoke hose" one for tire pump hose).
I taped up the exhaust and every other place I could find that smoke would come out that air is supposed to come out with rags and duck tape. If you look at automotive vacuum hose testing videos you'll probably see something similar. I don't know what other chemicals that smoke might be permeating the motor with, but i was at my wits end as well and since I bought the boat/motor/trailer for cheap enough to replace the motor if I had to I figured I didn't have much to loose and was worried that maybe the lower crank seal was bad but wasn't sure how to check it - the spray method seemed to put too much mist around the bad gasket surface as well... Been running strong ever since I got that intake smoothed off. (I think I used the back end of a big 3/4 drive socket with sand paper to smooth it off between the studs).

my guess on the oil is that it's just because you've been pumping oil in with the gas at a rich level considering you're not getting it to run at high rpm and it's just accumulating in the case instead of burning off. I had this problem also with a motor that got run at idle a lot in a bucket in the drive way after running it, there was always sludge stuff coming out of the prop exhaust. Never happened when it was run on the lake at regular rpm - just when run at idle for extended periods of time. (say 5-10 min while trying to see if it would get warm enough in the bucket for thermostat to open or to warm it up to check compression.)

Just a thought - when I was having ignition problems on one and narrowed it down to the plug wires, I also just bought the (sierra brand I think) plug wires that were already pre-made rather than fool with the spring that pokes into the core and what not... I just don't really like that system and the Evinrude "trim to fit" ones for my application were more expensive.

 

[Can'tFishEnough]

I finally finished the tread from the beginning (was looking at getting a similar motor so was interested in what all to look for during pre-buy):

I'm very curious how you tested the compression also: did you do it with one plug out at a time (like plug in on bottom and gauge on top) or both out at the same time?
Looking at the pictures of the head gasket (I assume the 6:00 position on the motor- 3:00 on the picture) in post #64 it does look like it had blown that gasket out. I'm confused how you were getting 155/165 (post #25) and 165/175 (post #51).
Any thoughts on why the compression was good even with the gasket in that condition? I'm trying to learn also and this just doesn't make since to me. When I got a tiny hole in a head gasket that looked very similar to that my compression went from around 120 to about 20. it was very obvious.

 

[jake83]

Well I made a little progress. The clamp on the shift linkage had loosened up, I noticed it when reassembling the foot. It was slipping and not engaging fully into reverse. Got that fixed.

Restarted the motor once everything was reassembled and no more revving up and down, at least on the muffs. But I am still having issues with the top cylinder. I took it down to a boat mechanic and he says I need a new fuel pump, water pump, and that the top cylinder is not getting spark. Kind of.

I think the next thing I will do is swap the two new coil assemblies and see what happens. Other than that top coil being bad, the only other part of the ignition system I have not replaced is the power pack. As of right now I am not willing to put anymore money into this motor though.

Good news is he hooked me up with a guy with a 90s model 40 hp force with power tilt and trim with tach and all controls for 500 bucks. Even better is that he needs some work done around his place so he is willing to barter. So now I can fish and make this a project motor, or maybe just sell the dang thing and get some money back.

As far as the compression, I removed both plugs and stuck my compression gage in one cylinder at a time. I believe the higher compression numbers were when the motor was cold. Concerning the head gasket, I don't believe it was bad, just old and kind of beat up around the water jacket. If it was bad, I agree with you, compression would have dropped severely.

I like your smoke test idea and seems like a good next step to try.