TOPIC: 3 cylinder Mercs ...Good or Bad ??

I got a chance to pick up a 70 something 3 cylinder Merc 70 HP .Are they not so good ?? I see alot of them on CL with bad power heads . Are they not as good as the 4 Cylinders ?? Anybody own one ?? How are they ??
Thanks Larry

Larry, I have a 1978 70 hp 3 cylinder.. they are rough ,shaking at idle I just pulled the carbs off cleaned the float chambers,,had a lot of old gas inside gumming up everything.. .I noticed if you set the idle up a little higher,you can it to smooth out a little. You can read some of my old posts,I had with the main electrical harness, it drove me crazy !!! The 4 cylinders run smoother ! Dr. Frankenmerc ... Whats your opinion on these ???

One of the problems with them is in the cooling system.

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Many failures due to loss of cooling on the upper cylinder.

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Result is a cracked dome around the top sparkplug.

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If cooling system is properly maintained you might be OK with one of them

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I prefer the 4 cylinder 650.

bobo
I know only one mercaholic that likes them

I found a guy who has one and wants $100 for it .Same old ran good last time used 5 years ago story .Its got controls with it but of course no key ..L.O.L..How do so many people lose Mercury keys ?? I checked You tube and there were a couple of Videos of them running . To me they sounded pretty crappy .I really dont have a use for it . Was wondering if they share maybe ignition parts , lower units as my 1150 ? Guess the controls would be worth at least 1/2 that .

professor wrote:

One of the problems with them is in the cooling system.

---

Many failures due to loss of cooling on the upper cylinder.

---

Result is a cracked dome around the top sparkplug.

---

If cooling system is properly maintained you might be OK with one of them

---

I prefer the 4 cylinder 650.

This was remedied by drilling a relief port at the top of the block and installing a telltale out through the cover. It prevented an air pocket from forming at the top cylinder.

I have a 650 3 cylinder on my Wacanda. It has been fairly reliable but I keep it clean, garaged and exercised. I don't like the sound at all, sounds like a sewing machine with something loose, a weird ringing sound. It has always had that sound (10 years) so I ignore it.
I have just put a new impeller, fuel pump, and plugs in her. I also cleaned out the bowls and she runs great.

Thanks Guys .. They sound GREAT ...L.O.L...Ive listened to them on You lube and most dont sound great ..Most of them on boats didnt look like Neck Snapping acceleration either .Maybe Ill stick with my 4 bangers and my towers .I just picked up a 63 650 4 Cylinder anyway .Points are easier to Diagnose a problem with than switch boxs and that Old recoil on top is nice just incase .Why did they do away with them ? Hell your Grand Ma could pull start the 650 .
Larry