SwervinMervin
Member
Hi:
I have an old Mercury 850 from about 1973. It ran great for about an hour. Then it started... It would come out of the hole great and run great for a hundred yards or so, then would suddenly bog and lose RPM. Maybe losing a cylinder? I'm no expert but that's what it felt like.
It always starts and idle beauty, even when I'm having my troubles. I had actually checked the compression before and after my trip. I checked the top 3 cylinders but can't get my gauge on the bottom one because I can't get around the bottom cowling. I get around 120psi on each. The plugs look a little wet. Temperatures are fine, I could put my hand anywhere on the engine. I was running it a bit hard before I had trouble, but I wouldn't say excessively.
I'm gonna go back to the lake tonight and see if I can go any amount of time without trouble, but I was wondering if anyone might have some ideas before I head out.
I feel like this is some kind of temperature related issue because I went some time before having trouble. I think I can rule out the plugs because the issue would come and go. Even without knowing the bottom hole compression I feel confident in it because the engine can run sweet, and again; the problem comes and goes. I can't totally rule out fuel, I'm betting on spark.
I'm not too familiar with Mercury engines but have a bunch of time wrenching on an old Johnson crossflow. I feel like after this problem, that should about do it - I've had every single possible boat problem a person can have. Man! Old boat engines!
I have an old Mercury 850 from about 1973. It ran great for about an hour. Then it started... It would come out of the hole great and run great for a hundred yards or so, then would suddenly bog and lose RPM. Maybe losing a cylinder? I'm no expert but that's what it felt like.
Funny thing was that I would stop the boat and start all over again, and same thing over and over again. Out of the hole and run great for a minute, then bog.
It always starts and idle beauty, even when I'm having my troubles. I had actually checked the compression before and after my trip. I checked the top 3 cylinders but can't get my gauge on the bottom one because I can't get around the bottom cowling. I get around 120psi on each. The plugs look a little wet. Temperatures are fine, I could put my hand anywhere on the engine. I was running it a bit hard before I had trouble, but I wouldn't say excessively.
I'm gonna go back to the lake tonight and see if I can go any amount of time without trouble, but I was wondering if anyone might have some ideas before I head out.
I feel like this is some kind of temperature related issue because I went some time before having trouble. I think I can rule out the plugs because the issue would come and go. Even without knowing the bottom hole compression I feel confident in it because the engine can run sweet, and again; the problem comes and goes. I can't totally rule out fuel, I'm betting on spark.
I'm not too familiar with Mercury engines but have a bunch of time wrenching on an old Johnson crossflow. I feel like after this problem, that should about do it - I've had every single possible boat problem a person can have. Man! Old boat engines!
