Let's get my 1974 Johnson 50HP running!

dixie460

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Mar 3, 2015
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12
Hey y'all, I'm a new member here! I'm new to outboards but not to doing my own work. I don't like owning things which I have no knowledge of, so to that end I'll be ordering a SELOC repair manual and/or a factory repair manual for my outboard. I'll be more than happy to help others out on here as I learn!

Anyhow, a few weeks ago I bought a 14' aluminum v-hull jon boat. It has a 1974 Johnson 50HP, model 50ESL74M, that's giving me some trouble and generally runs like crap. I'm trying to get it in good running order but right now it barely even idles long enough for me to push the fast idle lever down and get it in gear!

Here's the symptoms:
- Won't idle in neutral or in gear.
- Has more power at 90% throttle than it does at 100%.
- Hard to start (requires brief choking if it sits for more than a minute or two even after just having been run, also have
to crank it quite a bit)
- Sometimes, depending on throttle setting, seems to miss in one cylinder (engine is a twin cylinder).
- Doesn't seem able to rev to it's full speed, it will only push my boat to around 17 MPH.

And here's the story:

When I first bought the boat/motor, the guy selling it (private seller) said it would only run about 15 MPH and needed the carbs cleaned. I registered the boat and trailer and went down to the river to see what I was working with. First off, water pump is working and the engine stays cool enough I can leave my finger on the upper water jacket all day long. Took her out in the channel after having to crank it for several seconds, and she would barely stay running at idle as well. Around 1/4 throttle or so it seemed to clear up and run smooth, boat was doing around 5 MPH at this point. I opened it up to full throttle and the chartplotter showed a speed of 17 MPH which is about what the previous owner said to expect, and the engine seemed to surge as well.

Took it back to the house and, remembering what the seller told me about the carbs needing cleaned, I picked up two Johnson/Evinrude kits and pulled the carbs apart. Found brand new parts in both of them! Since I already bought the parts, I stripped each one down and blew all the passages out with air, removed the one jet that I found at the bottom of each bowl and made sure that was clear, and reassembled them both with new floats, float valves/seats, welch plugs, gaskets, etc. I also took the filter screen off the fuel pump and only found some minor debris in there, which I blew out with air as well. I set the idle mix screws back where I found them (1.5 turns out/open) and headed for the river again the next day.

Back on the river it behaved the same way as before, except now instead of surging at full throttle, it would just lose
power. Backing off to 90% throttle seemed to clear it up a bit but still only topped out at 17 MPH. Squeezing the primer bulb while running at various throttle settings didn't seem to affect the engine in any way.

I'm thinking because of the way it behaves at full throttle that I might have a fuel delivery issue, and since the carbs are clean, perhaps I need to take a look at the fuel pump and lines. Am I on the right track with this thought? What's the best way to test this, or is there something else I need to look at? I don't think it's ignition-related, although I read about outboard ignition systems and haven't ever worked on or diagnosed one before.
 

oldcatamount

Lieutenant Commander
Joined
Apr 4, 2010
Messages
1,740
Sounds to me like you're running on one cylinder. Get an "air gap" spark tester gapped to at least 3/8" and check the ignition at the plug end of the spark plug wires while cranking the motor over. You might need someone to turn the key while you are back there looking at the tester. If the ignition is ok, the spark will be bright blue, and jump the 3/8 gap easily on both wires. If it doesn't, look for cracks or burn marks on both coils. By the way, in my opinion, a 50 hp motor on a boat that small is dangerous (when running correctly).
 

dixie460

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Joined
Mar 3, 2015
Messages
12
Thanks oldcatamount, I'll give that a try and post back with results. As for 50 HP being too much for the boat, I thought so too but the boat's nameplate is well worn and completely unreadable from years of exposure to the outdoors, so I don't know what it's rated for. The motor came with the boat. It's okay though, I ain't trying to win any races with her, and I'd rather have more engine than I need and run at part throttle instead of having just enough to get by and having to run it full out all the time. Kinda like a bike or sports car... just cause it "can" go that fast doesn't mean it's a good idea!
 

gm280

Supreme Mariner
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Jun 26, 2011
Messages
14,585
If both the spark and fuel seems to be okay, what about timing? Is the base plate moving in relationship to the carb butterflies? Also do a compression test on both cylinders and let us know what you find out. Could be either stuck rings or low compression. Of course other issues as well, but you have to start somewhere and compression test is a good place to start. So do those tests with the spark and compression and report back with your results.
 

dixie460

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Mar 3, 2015
Messages
12
Got my compression tester, combination fuel pressure/vacuum gauge, and air gap spark tester in the truck with me today and after work I'll do the tests mentioned above and post back this evening.

I'll check compression with a battery charger hooked up to make sure the starter actually spins the motor well.

I'll also check out the timer base(?) under the flywheel and make sure that it moves with the throttle linkage. Also, I noticed timing marks on the flywheel. Does anyone know what the timing is supposed to be set at? I didn't see a timing pointer but then again I didn't really look either. I have a timing light as well so I can check it.
 

dixie460

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Joined
Mar 3, 2015
Messages
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Well, I got my answer as to why it runs the way it does. Compression on the top cylinder is 90 PSI, bottom cylinder is 60.

90 is lousy enough, I was hoping for at least 100 and preferably 120+ but oh well. The bottom one with only 60... well no wonder it wouldn't idle!

So do y'all think it'll be cheaper for me to buy the parts and rebuild this thing, or should I just get another motor? As mentioned above I don't need a 50 horse, I'm thinking a 25 should do just fine. I ain't seen too many 25 HP motors that are remote steer/throttle though... and this boat is a center console so I don't want to change to tiller steer.
 

64osby

Admiral
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Jul 28, 2009
Messages
6,799
Love to see a picture of the boat. A 14' center console.

Who made it? We might be able to figure what the max HP for the hull is.

The 50 might be a good fit for it.

The low compression could be as simple as a new head gasket, or it might be as bad as bad rings.

:welcome: to iboats.
 
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dixie460

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Mar 3, 2015
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I don't know who made it, the title shows it as homebuilt. The center console is an add-on that the previous owner said he had built, along with the casting deck up front.I'll take some pictures today and post them up!

Headgasket or rings... I was thinking the same thing but given the age of this motor I wouldn't be surprised to find it needs rings and a hone job. I thought about it last night after I posted here and I think I might tear into it just to have a look.
 

dixie460

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Mar 3, 2015
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Yep, I'll pull the head today after work. Still don't have a manual... I don't want to spend the $30+ on one if the motor's toast. If it's just a blown head gasket then I'll be more than happy to buy one to help me help this engine live on. Hopefully it's something simple. I wasn't able to run the motor before the compression test because it HATES running on muffs for some reason. Put it in the water and she cools fine.

What would I be looking for to determine if my rings are stuck? Scored cylinder walls?
 

gm280

Supreme Mariner
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Jun 26, 2011
Messages
14,585
Yep, I'll pull the head today after work. Still don't have a manual... I don't want to spend the $30+ on one if the motor's toast. If it's just a blown head gasket then I'll be more than happy to buy one to help me help this engine live on. Hopefully it's something simple. I wasn't able to run the motor before the compression test because it HATES running on muffs for some reason. Put it in the water and she cools fine.

What would I be looking for to determine if my rings are stuck? Scored cylinder walls?

First thing is to look over the head gasket for obvious blow out areas. You can actually see the stuck ring(s) on the pistons if they are stuck via the side port opening. And if the cylinders look smooth, have them measured to see if they are worn too far. Of course any serious score marks are obvious and will need to be addresses. Then you could be looking at a rebuild. But it is entirely up to you if that is the problem. Parts can still be bought for your engine and if the rest of the engine looks good, it could be a good rebuild effort. I rebuilt my '76 40HP Johnson and it came out amazing. If you want to see it, click on the title on my signature section and take a looksee... JMHO
 

dixie460

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Mar 3, 2015
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IMG_20150306_153121418_zpsefv28xuu.jpg


IMG_20150306_153522207_zpsieyffwl4.jpg


IMG_20150306_153539691_zpsa08lcrnl.jpg


IMG_20150306_154813528_zpse6g9m7qd.jpg


Okay, so as y'all can see the head gasket's blown. One cylinder wall has one light score mark, otherwise they seem okay. Not too worried about it. I have the new head gasket and will be putting it back together tomorrow after I resurface the head using some sandpaper on a flat surface.

I also picked up a water pump impeller. If this gets her running right I'll put that in too! I'll also try some seafoam after i fire it up again just in case a ring might be sticking.

Does anyone happen to know the proper head bolt torque and tightening sequence?
 
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dixie460

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Mar 3, 2015
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Also, yes I know the boat ain't the pretties thing right now. No idea why somebody though red reflectors on the transom would look good... they're going away! I'm gonna redo the center console so it actually has a front panel too. Probably add a radio to it so I can tune in to Country Gold Saturday Night, rewire the entire boat, fix the bilge pump, and probably paint the whole thing.
 

boobie

Supreme Mariner
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Nov 5, 2009
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20,826
18-20 FT-LBS head bolt torque..Start in the center and work your way out in a spiral pattern torqueing the bolts in steps until you reach 20.
 

gm280

Supreme Mariner
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Jun 26, 2011
Messages
14,585
Yes make sure the block section is also perfectly flat as well. Maybe your compression will be fixed now... Let us know how it works out.
 

64osby

Admiral
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Jul 28, 2009
Messages
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Maybe the reflectors replaced the anchor light?

As a quick observation after seeing the hull, that 50 is way too big for the hull, also was stated prior. I would think a 20 or 25 would be a good fit.
 

dixie460

Cadet
Joined
Mar 3, 2015
Messages
12
I think it's a bit big for the boat myself, but that's what I have to work with and at least I'll never be on the river trying to go against the current and wishing I had a bigger motor. Lol. If I get it running right perhaps someone will want to trade for a 25 with controls... but of course then I might be inheriting another problem.

Anyhow, I got the head and block cleaned up, and Gulf Coast Marine (great guys by the way) had the head gasket in stock when I went by there yesterday after pulling the motor apart, so I got it all back together today and did another compression test. Got 110 PSI on both cylinders! Towed it down to the ramp and she fired up without much fuss. Runs okay at lower speeds. Idle is high but that appears to be a linkage problem... if I force the idle lower it eventually sputters to a stop. Think I need to adjust the carbs now, but first I have another problem or two.

First problem is she still misses once in a while especially at higher throttle openings, still has about the same top speed of 20 MPH. Might be the wrong prop on there too... not seeing any numbers on it. Also have it trimmed to the second to lowest stop on the manual trim adjustment. I'll play with prop and trim when she runs better.

The other problem is this:

IMG_20150307_184448421_zpsdk54cavu.jpg


Battery wasn't charging so i looked up under the flywheel and found this. I was wondering what the hard glossy stuff was that was on top of the motor... now i know. It was there when i went to look at the boat and kinda looked like dried old Permatex, so my dumb self just thought the guy was a sloppy mechanic. Now careful inspection shows it's shellac or something dripping from the stator coils. Given my limited knowledge of outboard ignition and charging systems, I assume this is one of the charging system coils since the battery won't charge. But being that the stator is all one piece, this could affect my ignition too, right?

Thanks for all your support, I really appreciate it!! Have a great weekend.

Oh and I got a repair manual on the way. I can't see where to drain the lower unit gear lube, and I want to change it both because I don't know when it was done last and also want to make sure I don't have any seals leaking.
 

64osby

Admiral
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Jul 28, 2009
Messages
6,799
After you fix the stator, check spark on the cylinders. Sounds like it could also use a carb clean / rebuild.

I have a 14'er with an 18hp tiller and it will do 23mph.
 
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