1972 50hp Johnson Compression?

[Paulywog0667]

I finally found a couple welders for the lower assembly housing if need be, but need some honest feedback on compression. I baught a compression tester, took out one plug at a time and tested right around 95psi at both plug threads. They tested the same, but I've read wanting over 120psi? I also picked up a carb kit and two plugs. If the carb kit works with plugs, is 95psi going to hold long enough to dump $200.00 into a lower project and some gear oil? My buddy will weld any aluminum I give him for $100.00 of the $200.00 unless I get him mad. If 95psi is only long enough for the scrap yard though... I picked up a bilge pump, fuel tank and fuel line too. Probably tested right at 96-98 each, but seems they leveled both at a heavy 95-96 by the time I saw definate pressures.

 

[racerone]

My tester would show 140+ PSI on a good motor.

 

[jbuote]

I'd test it with both plugs out.. (better cranking speed)..
​and yes, you should be as racerone stated.. 140 or above..
would probably run with around 100, but it's not good.. lol

​If it runs at all, you could try a decarbing on it before shelling out money on the lower and maybe free up stuck rings (if stuck) but that's not a huge compression boost..
Could help it though..

I have a 71 Johnson 50 and I get 170psi on both for a reference...

 

[joeanna]

I get 95psi on both my 2 stroke cylinders warm, about 90 cold on a 2000 Johnson 50hp. It runs good, but I have also never checked my compression guage for accuracy yet? It could be way off,.,.,.,

 

[racerone]

But the 2000 model is NOT THE SAME as a 1972.----The newer motors have a wee hole in the cylinder wall for compression relief at lower speeds.----Makes for a smoother / quieter running engine.

 

[Paulywog0667]

Thanks everyone, I went back out there and finger snugged the o-ring on the compression tester. An easy 100psi without any tricks and one plug still in. I didn't want to snug the tester too much. The motor was free and sitting for years. The carb kit I picked up and get home to see I might need two. I'm hoping a good go over of seals and gaskets. I'll take the carb off tomorrow and do some cleaning, while putting the volt meter on the electrical.

 

[Paulywog0667]

I went back outside and sprayed a little WD40 into the two plug spots. My buddy mentioned something could have been slightly bound from sitting. Low battery charge and immediately up to 115psi. Called the local vintage outboard guy and he mentioned udually able to reuse carb parts on those outboards, but I have a kit with float incase. Over 120psi will probably be really easy, but once it starts and lower gets welded, I'll search the site for what type of lower seal kit I'll need. Being broke sucks, but I probably made the money seem more by looking at the lower before starting it.

 

[Paulywog0667]

Cleaned up one kit worth of carb. I need to get another kit. Things are a little gummed up at the floats and the mid gaskets were both bla, but the carb project seems easy enough. My next to nothing worth of engine skills lead to not realizing having to pick up two kits. If there's no lower on the motor would that effect cranking pressure? I didn't bother putting it back on to test from going to do the seals and impellor. I read someone elses thread and saw something about back pressure with the boat actually in water.

 

[GREE]

You could check your head gasket to just be careful taking it off, cause my 1973 115hp showed 90 psi and I noticed there was like a black ring around the gasket replaced it and 120 psi after sitting for 30 seconds and the rest read the same but idk if it'll help you out just throwing a suggestion out there. These guys know a lot more then I do lol.

 

[jbuote]

No, your compression test results are not affected by having the lower unit on or off..
​The backpressure is on the exhaust when the engine is running, and in the lake..

​You could pull the head and check the gasket, but I think your compression results would be quite different between the cylinders if the head gasket were an issue.
​Usually, 1 cylinder compression test would be WAY lower than the other(s).. That's usually the sign of a gasket issue.
​But if there is a gasket issue in the center between the 2 cylinders, then it could keep it even I guess..

​Your choice on pulling the head and checking it..

 

[Paulywog0667]

I've been debating that with the carb unit being off anyways. Anything that comes apart is probably a, needs a o-ring or gasket. The wife and I baught the wife a new car. Making my tight pockets even more tight than normal. Just the fuel tank, hose and primer bulb ran around $140.00. Now it's at around $175.00 and still not running. Lol

I went and took the filter cap off the fuel pump and need to locate fuel hoses on the website too. I think the 110-115psi I got both up to with a little WD40 will have to hold over until I see it start. Might not be a new 50hp. performance, but a day on the water makes spending easier. Lol.

 

[jbuote]

I hear you! LOL
​And, if you can get it running with the lower compression for now, then it'll allow you to further troubleshoot anything else that may be an issue you haven't found yet.. LOL

​Good Idea to get it running to see if it ALL works.. (shifting, cooling etc..) then you have an overall picture of the engine, and can make a plan for any fixing/spending.. lol

 

[Paulywog0667]

I hear you! LOL
​And, if you can get it running with the lower compression for now, then it'll allow you to further troubleshoot anything else that may be an issue you haven't found yet.. LOL

​Good Idea to get it running to see if it ALL works.. (shifting, cooling etc..) then you have an overall picture of the engine, and can make a plan for any fixing/spending.. lol

I can't believe I took off the lower assembly before starting it. I racked up $300.00 in spending lists for what could have been $35.00 for two carb kits. I've shaken my head at myself a few times, lol. Once over 100psi. it seemed it might be worth a little money. If I was a mechanic and knew it would start, then I wouldn't have sticker shock. Reality, I needed a fuel tank and primer bulb for any motor.

 

[jbuote]

Well, you'll want a new impellor once you get it running, so taking the lower off isn't that bad.. haha..

​I should add to my previous comment though... With compression that low for a 72 50hp, you can bank on needing to do one of, (or all of) these:
1) Decarb.
2) Head Gasket
​3) Rings.. .(This is a major deal.. Whole engine comes apart, pistons out, hone cylinder walls etc... Basically, a full rebuild from scratch.. )

​Now, what I meant with previous comment, was that getting it running will give you the whole picture..
You may choose to spend a little, have it run, and use it until it dies then junk it..
OR
​you may choose to run it till it dies, then full rebuild..
​Or, even run, and use it for a bit, but rebuild anyway in an off-season..

​That's really what I was getting at.. LOL..

Gear oil.. You said it's a 72.. That's Hydro-Electric shifting..
​Use only Type "C" gear oil.. (A.K.A Premium Blend)
​Be careful when getting it though.. I've read that some claim to be type c, but aren't for electric shift..
​I personally got some Type "C" that states "for electric shift" right on the bottle of gear oil.. LOL

 

[Paulywog0667]

Well, you'll want a new impellor once you get it running, so taking the lower off isn't that bad.. haha..

​I should add to my previous comment though... With compression that low for a 72 50hp, you can bank on needing to do one of, (or all of) these:
1) Decarb.
2) Head Gasket
​3) Rings.. .(This is a major deal.. Whole engine comes apart, pistons out, hone cylinder walls etc... Basically, a full rebuild from scratch.. )

​Now, what I meant with previous comment, was that getting it running will give you the whole picture..
You may choose to spend a little, have it run, and use it until it dies then junk it..
OR
​you may choose to run it till it dies, then full rebuild..
​Or, even run, and use it for a bit, but rebuild anyway in an off-season..

​That's really what I was getting at.. LOL..

Gear oil.. You said it's a 72.. That's Hydro-Electric shifting..
​Use only Type "C" gear oil.. (A.K.A Premium Blend)
​Be careful when getting it though.. I've read that some claim to be type c, but aren't for electric shift..
​I personally got some Type "C" that states "for electric shift" right on the bottle of gear oil.. LOL

Full rebuild is not a big deal once I know it will start and stay started. For right now between learning fuel lines and debating what and if something sat in the fuel pump. More of a, knowing the lower should go back on with water pumping to start it, but I already have it half apart and battling morals of firing the motor for a few seconds. Not wanting to spend money on the lower until the motor starts though. A complete newbe mistake of not buying two carb kits and hooking the hose up to it. I can probably rig a hose under without putting the lower on too. Everything got push back a month from deciding to go new on the fuel tank.

 

[jbuote]

More of a, knowing the lower should go back on with water pumping to start it,.

Ahhhhh.... Now I understand what you meant.. lol

​Yeah.. you want the cooling for sure when trying to start it..
​Hadn't thought of it, but yeah.. Maybe you can rig up a hose on the water tube or something..
​After all, when on muffs, the impellor really doesn't do anything anyway.. It just lets the hose water pressure past it..
​As long as you can secure the hose in such a way you get water flow through the engine and back out again, you should be ok for at least short (1-3 minute runs) for testing.. (I think.. Not an expert, never tried it.. Up to you if you try it or not.. lol)

 

[Paulywog0667]

Got the motor started! Loud thing that it is. Lol I do need to study a little on tuning the carburetor(s) or find someone to do it. It starts, but seems to want to run for 10 seconds and then off. Taking the thing off, there was a little spring I wasn't too friendly with and need to study the electric choke part. Soon as both plugs where connected and turned the key with a charged battery and started right up. I duct taped the garden hose to the inlet, but didn't turn it on one time by accident. Think that means the therostat works? Lol

 

[jbuote]

Basics of carb tuning..

http://forums.iboats.com/forum/engi...nts-for-asorted-carb-variations-by-joe-reeves

​You'll want to look up and do a link & sync on it too...

 

[randyray41]

BOAT= Break Out Another Thousand!!! They all money pits but as part of any type enjoyment it costs $$$