1974 Merc 650 3cyl common problems?

[greenz]

I just bought a boat with this motor on it last year for a song and dance. I've had it on the lake a few times, finding out it didn't charge, on the last time out. It ran great, reluctantly starts when cold, but once it does, it starts on the first hit of the key. I also found the lower end leaks oil at the prop, has some play in it and i'm planning on taking it down when i do the impeller, hopefully its simple as bearings and seals. But thats what this post is about, I'm planning on taking this rig up to canada for our fishing trip for a week, Hopefully problem free. Does anyone know of any common problems or helpful tweaks for this motor? The trip isn't till june, and hopefully i'll be out on the local waters starting in the next couple weeks to run her alot and test the durability. But sometimes its faster to ask the pros to find the problems before they happen. Thanks for any help!

 

[jbjennings]

Re: 1974 Merc 650 3cyl common problems?

I own 2 of them, not because they're my favorite motors, but................
They both run good. One has a water jacket held together by JBWELD, because the previous owner got it hot and it cracked down all 3 cylinders under the exhaust cover. I hear that is a common problem when these 3 cylinder mercs overheat. Other than that, I really don't have a lot of problems with mine, and they actually crank very easily cold or warm (something not all mercs do that I've owned in the past). I'd check and make sure the solenoid is closing both choke plates FULLY CLOSED.
You already know you'll have to reseal the lower unit. Hopefully your driveshaft isn't grooved too bad to hold a seal. Reliable sources say you can sleeve them easily. Make sure the timing stop is in the right place or you could have detonation and put a hole in a piston. (just set the timing properly----it's probably already correct). A new rectifier will probably solve your charge problems and they're not all that high and easily changed out. I'm not a MErc expert by any stretch but have received lots of expert help here.
Good luck with your 650,
JBJennings

 

[greenz]

Re: 1974 Merc 650 3cyl common problems?

thanks for the tips, it seems to be a solid motor, the few things i mentioned i would've expected outta a 36 year old motor. I appreciate it!

 

[jbjennings]

Re: 1974 Merc 650 3cyl common problems?

I forgot to mention, it's kind of annoying to get those dual carbs for 3 cylinders to idle correctly. They want to either run too lean or too rich. One of mine is a good idler (the one with the bad water jacket), and the other one I use the most is not so good. The powerheads of the 3 cylinder mercs are known to some as the worst mercury ever built. However, I use mine regularly and so far haven't been stranded----knock on wood. I think the 4 cylinder merc 65hp motors were so awesome that the 3 cylinders may have been doomed to be stepchildren from the start.
Later,
JBJ