Hi, I like to boat and fish on the river, and just bought an older (18') flatbottom boat with a 1973 Mercury 650 65hp motor. Seller says the motor ran well.
Is it possible to keep this motor reliable, or do motors of this age become unrepairable? Monday I am going to have the local Mercury dealer give it a look before I put it in the water. I'd hate to run the boat for a few hours and screw something up. The seller had the boat out last weekend, and says that he just replaced the fuel pump and impeller.
The cowling is in sad shape, held on by a large bungee cord keeping the clam halves together. Can these be found anymore? I did some searching yesterday and it seems like it's hit or miss with motors this old. Does no one replicate cowlings?
Any motor can be made to be reliable, it all depends on how it is used and cared for. Unfortunately, the 3cyl Merc 650 is not known to be one of Merc's best designs and has had reliability issues more frequent than the norm. As a new owner, double check the compression on each cylinder and ensure the ignition timing is set properly (slightly less than what would be shown on it, to be more compatible with today's fuels). I'd at least inspect the water pump impeller, if not replace it. I generally won't trust a previous owner, and they should be replaced bi-annually anyways.
That's a large boat for a 65hp motor, but being flat bottom I suspect it must be a lightweight boat. Be sure to prop it so that you can reach maximum rpm at wide open throttle, then run it happily at cruising speeds say near 4500 to 5000 rpm on plane.
If your compression test yields low compression an any cylinder, its not the end of the world but you might want to be pro-active to slow down any wear where you can. Within 10% of each other and it should be okay. The 3 cylinders motors do idle a little rough (shakey), but not much you can do about that.
As for replacement cowlings, you best bet would be to find an old parts motor and swap it out or visit a local boat yard and see what they have kicking around. They are out there, and depending on your geographical location it may be easy or difficult to find one. I've also purchased a few cowls on eBay or craigslist from time to time.
I had the same motor as yours,but a 1975 model. Ran it for years but I neglected the impeller,and I lost the #1 cylinder. See your private msg for more info.
Thank you both for the responses. It is a pretty big boat. It's also older. It is a 1980 Alumacraft riveted hull. It is 18' long with a 74" beam. I'm not sure what hp it is rated for and I don't know how much the hull weighs or what capacity it has - I will be researching this soon because I plan some modifications including aluminum flooring, extending the aluminum decking, and will have a generator to power lights for bowfishing. I'd hate to have too much weight in the boat.
The aluminum work will come first, then I'll deal with the engine. If it's nice in the morning, I'm going to go put it in the water and see how it floats, how well the motor really is running. Once I start the aluminum work, it won't be on the water for a while.
1) Replaced a leaky fuel line.
2) Checked all spark plugs for spark.
3) Will be replacing lower unit fluid today.
I know I need to replace the pee tube running around the back of the motor housing and out the pee hole. The tubing is worn and not connected to the pee tube output. I'm guessing it would just shoot water all around the inside of the cowling if I ran it now. Probably not a good thing.
I'm not sure how hard it is to change an impeller, but I will be researching this as well.
Hi! New Boat Owner
Linear Mode
