1979 Mercury 40hp 2 Cylinder - Help

Hey Motorheads - I am seeking wisdom. I have a project boat and it came with this motor. I was really hoping to make it work, but I am having doubts. The wiring in the boat is a mess. To get a sense of the motor, I jumped the starter directly to see if it would turn over. With the spark plugs removed, it turned over really well. With the plugs installed, it would turn over, but very slowly. This is with the battery from my truck, which turns its V10 over just fine. I was jumping post to post straight through the starter.

I pulled the starter and took it apart. Cleaned everything up, brushes looked good. As part of the reinstall, I soldered in splices to repair the badly cracked wiring. A common problem on this vintage engine, I believe. Anyway, the motor still turns over very slowly. (Too slowly to start. BTW- I was never expecting it to fire. Just trying to roll it over.)

Anyway, I am starting to have second thoughts. I really need tilt/trim and I would like a reliable motor. As you can see, the skeg is also broken. So, as I see it, I am going to spend $600 for tilt/trim and $100 skeg repair - and that is before I get it running. I know it ran 5 years ago, but it was left unattended since that time...no telling how she stands today. Gear selector seems functional, as it would turn the prop correctly with the starter turning everything over.

Here's the motor, note the skeg:


Here's what the wiring looked like when I removed up the engine cover.


So what do you guys think? Fix her up or what? Or am I better off picking up a newer used 40hp with factory trim/tilt? Does this motor have a

The cables that you where using to jump it might not be thick enough gauge to turn it over. My brother motor had the same problem good starter, good battery, and it wouldn't turn fast enough to start it. We grabbed a second set of cables to jump the starter with and it would cranck till the cows come home. We just ended up getting some bigger battery cables and he hasn't had any problems since then. As for fixing the motor or buying a new one is your call. Don't know alot about the mercs. I guess it depends on the time and money you are willing to invest in the motor You could always part out the powerhead and mid section on this motor and buy a newer one.Hope this helps some.

I own a few Mercs.The electrical can be a challenge some times.I would take compression reading & see if it has spark & go from there.

BTW - where I come from, Motorhead is a compliment.

huntingbronco said:

BTW - where I come from, Motorhead is a compliment.

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Isn't it a copmliment every where :mrgreen:

I'd go with you're just not getting enough juice to the starter. It does turn over, so it answered your question on that right? But unless you are powering everything else it will not start with the power only to the starter. Since it turns over, you might be in good shape. Tilt/trim is nice, but not a necessity. And craigslist might have tile/trim for a decent price - I know I've seen them for $200ish

Skegs... well, my dad ran one for a long time with it broken off like yours. All it does is protect the prop, and provide a tiny bit of rudder action.

Hey guys - the latch that holds the front cover on is broken - anyone know where something like that can be found or do I need to fabricate something?

The latch on the back of my suzuki cover was broken... so far i put a stainless eye in it and use a rubber bungie to hold it down... As for the motor, if it were me i would fix it, because that just seems to be what i do, usually what can go wrong does too haha, but i learn and have fun.

Great news!

As I was about to give up on this motor - I decided to do a compression check. Mind you, this was after stripping her off the boat with controls and everything. Hooked up the wiring and the key worked! So did the choke button! (Neither worked when installed on the boat. When I keyed it over, she turned over like an engine is supposed to, not this struggling, barely turning over thing I had before. I was shocked. I thought my luck was turning. So, I had my son come out and hold the compression gauge while I turned the engine over. Much to my surprise - he exclaimed "there's spark"! This thing just might run!

Dry compression checked out at 125psi on the top cylinder. I could not check the bottom cylinder, but that is good enough for me to continue forward with the engine. Went ahead and changed the impeller and housing - screwed up the reverse lock out cam, so the lower unit is coming back off.

Only thing left at this time is to wonder if the carb is going to need rebuilding - I am guessing yes, given the fuel in the tank looked like mud. We shall see. Tank is cleaned, new bulb and fuel lines to the motor. Probably should flush the fuel in the carb - but it has been in there for 5 years - maybe its dry, if I am lucky. I'll report on that next week.

Congrats! Carb aren't all that bad

Always check connections when dealing with 12v, to the point of loosening them just to disturb the connection, then retighten.

Jumping the solenoid , battery positive to yellow wire with red strip should be all you need to do if all connections are tight and battery is hot, and solenoid is good. All I usually need is remote a starter button.

Mercury wiring is the pits from back in the 70's/80's. Going directly to the starter is sometimes all you can do.

Okay - had her running on the hose/muffs in the driveway last night. Little concerned about the lack of water flowing out the pee hole. Motor was getting hot. With a little vacuum, I could get water to flow out the pee hole with motor running on higher RPM - but it would not pick up itself. Hopefully this is normal, I'll see if she works in the lake later, unless you guys have a suggestion on what I might have done wrong.

The fuel lines were a mess - I am thinking at a minimum the carb needs to come out and be cleaned. In your experience, is that all I need to do? Or should I try to find a "carb rebuild kit" and use whatever parts it includes? As always, your advice is appreciated..

huntingbronco said:

Okay - had her running on the hose/muffs in the driveway last night. Little concerned about the lack of water flowing out the pee hole. Motor was getting hot. With a little vacuum, I could get water to flow out the pee hole with motor running on higher RPM - but it would not pick up itself. Hopefully this is normal, I'll see if she works in the lake later, unless you guys have a suggestion on what I might have done wrong.

The fuel lines were a mess - I am thinking at a minimum the carb needs to come out and be cleaned. In your experience, is that all I need to do? Or should I try to find a "carb rebuild kit" and use whatever parts it includes? As always, your advice is appreciated..

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The water pressure from the muffs themselves should push some water out the hole - at least it does on my 50hp.
Two things to try, reposition the muffs over the entrance holes (and turn on water full blast) - or get a garbage can and put the motor in this. I usually use this method to test it, there's less mess while you're working on the motor or boat. Just one big mess when you are done.
Maybe the waterpump isn't working?

As to carbs, sometimes it just needs a rebuild kit done to insure the fix lasts. If you can wait for it to arrive and then another night to rebuild them, that is what I'd do.

Thanks WASILVER - I think I found a carb kit locally. We'll see if I can get it done tonight.

I just replaced the water pump housing and impleller. I am always concerned that I don't get a good seal on that tube that extends up from the waterpump to the engine. I suspect if that seal is not good, water pressure will not be good. Wish I was more confident in my installation - I just don't do it enough to have a feel for it.

Carb came out, cleaned up, gaskets replaced and slipped back in. We'll see if she runs better on Saturday - going to try her in the bucket, see if the water pump is in fact working correctly.

Not sure about Mercs, but Johnson/Evinrudes have holes in the lower unit to let the water drain out; it's best to tape them up if you're running muffs. I like a large trash can best myself for driveway testing.

Skidz

Thanks Skidz.

Got the engine in the tank tonight. Ran much better and I had a great stream from the water pump.

Question - engine would not run real well without the choke partially on. Is there a chance the fuel pump needs rebuilding or is this something I did wrong in the carb rebuild?

Could be both.Try squeezing primer bulb while running to see if it makes any difference.If not try turning out the idle adjustment.

Craig - thanks. I squeezed the bulb - it got firm and held pressure. (It did not get soft while running.)

Operating the engine at everything but very fast required choke to maintain operation. This was in a tank, no prop. I'll look into symptoms regarding fuel pumps. Seems to me with all of the jets cleaned and float functioning, it would not likely be the carb. I did not dissasemble the need valve above the float, it was washed really well from above and blow and it seemed to move freely. Pretty simple single carb setup. Of course, I might have overlooked something in the reassembly.

How does a fuel pump needing a rebuild evidence itself?