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'73 Johnson Troubles

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jdschwass

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Hey'all,

As the title says, I am having some issues with my 1973 Johnson 20HP long shaft.
I got it with a boat I picked up recently, and compression was excellent (120 top and bottom), so I decided to try and get it running.

After replacing points, condensers, primary coil, plugs, and a carb cleaning, I finally got it running kinda sorta in a bucket. I think it needs to open up on the lake to clean out the carbon though. Still a bit rough.

I replaced the impeller and the thermostat before anything. I also stuck a couple of new o-rings on the driveshaft tube. Now that it's kinda-sorta running in a bucket of water, I can see water draining out from the lower unit. There is a hole(s) on the front side of the lower unit facing the transom that is draining water. Is this a sign that the water tube is leaking inside the housing? Or something else is leaking? There is water blowing out with the exhaust, so at least some water is getting to the powerhead.
If the boat was in the lake, you may never notice the holes draining water, so maybe it's not an issue. I just want to know if I have to reseal the lower unit before spring.

I have to wait until spring before I can get it into the lake, so until then, it's all bucket testing.


Thanks all.
 
jdschwass said:
Hey'all,

As the title says, I am having some issues with my 1973 Johnson 20HP long shaft.
I got it with a boat I picked up recently, and compression was excellent (120 top and bottom), so I decided to try and get it running.

After replacing points, condensers, primary coil, plugs, and a carb cleaning, I finally got it running kinda sorta in a bucket. I think it needs to open up on the lake to clean out the carbon though. Still a bit rough.

I replaced the impeller and the thermostat before anything. I also stuck a couple of new o-rings on the driveshaft tube. Now that it's kinda-sorta running in a bucket of water, I can see water draining out from the lower unit. There is a hole(s) on the front side of the lower unit facing the transom that is draining water. Is this a sign that the water tube is leaking inside the housing? Or something else is leaking? There is water blowing out with the exhaust, so at least some water is getting to the powerhead.
If the boat was in the lake, you may never notice the holes draining water, so maybe it's not an issue. I just want to know if I have to reseal the lower unit before spring.

I have to wait until spring before I can get it into the lake, so until then, it's all bucket testing.


Thanks all.
Click to expand...

Well I may have answered my own question...

Being a little bit impatient, a little bit bored, and plenty of cabin fever, I removed the lower unit to inspect.
The holes which I was referring to are located facing the transom between the grease nipple and the cover for the shift linkage. Clearly these holes are drilled in the casing to act as a tell-tail if the crankshaft tube seals fail.
I guess when I installed the lower unit before, the oring got cut on it's way into the upper housing. It held for a bit, but ultimately failed.

I installed another oring, and carefully installed it this time making sure it was seated. Fingers crossed that all is fine.
Can't wait to get this thing in the lake so I can run it properly.

Thanks to anyone who took the time to read.

Cheers.
 
That hole is likely a casting cavity drain, it prevent freeze cracking of the casting.------It is supposed to leak when motor is taken out of the water.-----Have seen those plugged with sand / mud and the casing cracked.-----Or plugged with RTV by those that do not know the purpose.
 
jd, if I am reading this correctly, you are speaking of the drain hole(s) for the drive shaft isolation tube. Water is supposed to come out there when it is running. It is water that has escaped from the water pump and is normal and intentional. It is not any kind of tell-tale.
 
Right. That driveshaft tube is not used on some motors. I think only on longshaft using the housing spacer. Be sure water level is at least 4" above the water pump area. I get a little nervous when I hear the word "bucket". Also note when you're running in an enclosed area, where the motor can't get enough fresh oxygen, it may tend to run rough. Try removing the cowling and set up an electric fan to supply fresh air.
 
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Thanks for all the feedback! I am glad I checked anyways, because the o-ring was damaged. Interesting though, glad I asked!
When I say bucket, I mean large garbage bin with 25 gallons of what is ice cold water right now.
I am running it outside, I hopefully oxygen isn't an issue.

I have heard engines don't run as well when they arent in the lake. Part of my problem is I can't run it other than in neutral or the prop displaces all the water. When it's in neutral, the throttle is quite limited. I bet a few minutes of full throttle operation on the open water would help this motor out.

With any of these old 2-strokes, my concern is the crank seals. With the old snowmobiles (from the early 70's) I have had motors running great, and die on the first trip due to crank seal failure. The symptoms are similar to what I am experiencing now: won't idle down, rough running, then dead. Running way to lean due to excess air getting sucked in is a concern. Just not sure if I want to get into proactive replacement.

Appreciate the input.
Thanks.
 
The bottom seal is a carbon seal with an o-ring.-----Very durable.-----If the upper seal was bad then you would have seen oil all over the points.----Seal between crankcases is a metal " labarynth " seal also very durable..----Some more trouble shooting required.-----Checked the reed valves ?-----Checked / replaced fuel pump diaphragm , less than $10 item ?
 
Right, Racer. The fuel pump diaphragm leak will introduce excessive fuel into it's operating cylinder. Won't be as noticable at high speed. The fuel pump will still work too. This problem is more common than you may think.
 
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That's a good point, I plan to replace the pump seal regardless of condition. My old '70 Merc 800 had one poor diaphragm and one that had a hole right through it. It caused a rich condition due to drawing fuel right into the crankcase. That will be next on my list for sure.

I am glad to hear that crank seals aren't a major problem. The old snowmobile seals were just a rubber lip seal and prone to cracking and getting vulcanized after years of use and/or sitting. I have no evidence of upper seal leaking right now, so that's good.

I am determined to get the old girl up and running. Thanks again.
 
So I pulled the fuel pump off this morning. The outer gasket is pretty punky, but the rest of the soft goods appear to be in decent shape, or at least appear not to have any rips. Planning to replace the bits anyways, I came on here to find the parts, and now I am a bit confused.
For reference, my serial # is 20R73A

Searching fuel pump parts, I can find gasket part #2 and #6, but none of the parts within the pump itself. There is a part number for the pump assembly and housing, but it's significantly more than the price of a diaphragm.
What's more, the picture of the pump seems to be different than mine. The picture shows the fuel line barb, and a second barb which I assume goes to the carb. The FP on my motor has no line to the carb. I figured the crankcase pressure runs the diaphragm, and that's it.

Am I missing something? Thanks.
 
It shows the little square pump.-------The diaphragm is available all day long.------It was just not listed in the 73 catalogue.-----It was first used in 1968 and that diaphragm was also installed in 2005 models.----Start looking at 6 / 8 / 9.9 models fuel pumps beginning in the late 1980's.----I could post the part # but then you won't learn anything !!
 
Thanks for the info: Looking at the 2005 model I found the repair kit that looks to be the same.
I will get that ordered up!

Cheers.
 
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