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1978 Johnso 70hp Stalls when put in gear

S

stumpnocker

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"Hi, please help!
My engine s

"Hi, please help!
My engine seems to run fine out of the water, accel / decel ok, in neutral or in gear.
When the boat is in the water it's a different story. Idles fine when started, but when I put it in gear it immediately stalls the motor. Doesn't matter if it's forward or reverse.
So I pulled the plugs. They are black and seem carbon fouled. I put a compression tester in and the top cylinder measures only 60, middle 100, bottom 90. While testing the compression I also checked the spark - all 3 plugs seem to have a good blue spark. The compression seems real low... what are the possible problems and where do I start?
thanks in advance!"
 
"you could try cleaning the ca

"you could try cleaning the carbs, there might be to much difference in the compression to let it run under pressure when in the water, sounds like you need to rebuild the engine"
 
carb cleaning I can do but my

carb cleaning I can do but my knowledge of boat motors is nil. What all is involved in the rebuild? Where can I buy parts?
Thanks again...
 
"ok next question...
I took t

"ok next question...
I took the carbs apart and installed new gaskets. The internal parts were clean, like brand new.
I took the screen off the fuel pump and noticed some gunk in there... so I took the pump apart... and broke the plastic piece. Dang it. Now I need a new pump. I looked up the part # and it comes up with 0385784, with several supercedes, ending up with 0438559. But those two part numbers are different... the first shows 3 hose connections (which is correct) but the last shows only 2 conncetions. What am I missing here?
thanks"
 
"I had one of those motors onc

"I had one of those motors once. They are junk. If
you have a weak fuel pump,or one of those carbs
becomes fouled, you will instantly burn a piston
or worse some bearings and cylinder also. It may start on one cylinder and be burning up the others without you knowing it....Good luck."
 
before you spend money on a fu

before you spend money on a fuel pump pull the head off and have a look inside.

your cyls need to be within 10% of each other to run correctly.

fuel pump or not your compression is too low in one cyl

post back what you find.
 
"78,70.......is one of the bes

"78,70.......is one of the best engines,omc ever made.....lack of proper maintenence,...is junk!"
 
"i agree with jwb i have a 78

"i agree with jwb i have a 78 70 runs great engine has plenty of power, last owner neglected it i had to rebuild it but it was worth it. its all in the maintence. well put jwb"
 
"ok, more info
I was told the

"ok, more info
I was told the compression test shouldn't be done 'dry', so I took some 2-stroke oil and squirted it in the spark plug hole with a syringe. Re-tested the compression - top cylinder 90, middle 100, bottom 90. So the 3 are closer together but still kind of low?
I'm reluctant to pull the head unless I really have to since my mechanical skills are not exactly professional grade.
The previous owner told me he had the rings replaced. Included with the sale was the paperwork (invoice) for a set of rings dated April 09 so I assume it was done. Is there a chance the mechanic screwed something up? I would expect higher compression with a new set of rings, right?"
 
the oil is just filling in the

the oil is just filling in the gaps. makes the numbers jump on the comp tester. try running the unit for a minute or two then testing it. will have gas/oil on cylinder walls and should give good proper reading. Units that sit too long get dry cylinders and will give a false low reading.
 
"Well,when I bought my motor i

"Well,when I bought my motor it had just been rebuilt also. It would like to start on 1 or 2 cylinders. Die when put in gear. I took the carbs
apart and there was no spring clips on the float valves. When the float dropped,it would not pull the valve open.I don`t know if OMC made them this way or not.So if a valve stuck shut,it would lean out that cylinder,frying it. My brand new so-called just rebuilt motor was toast, and it had to be rebuilt again. You might be in the same boat."
 
"nope, checked that and the in

"nope, checked that and the inside of the carbs are perfect as far as I can see. Spring clips there, new gaskets installed, everything really clean."
 
"See if you can locate a bore-

"See if you can locate a bore-scope and look down the spark plug holes. Auto parts stores may have one to use,or buy one on e-bay like I did."
 
"Joe, In my limited experience

"Joe, In my limited experience a reuild is the only ption. My 77 70HP had low comp in one cylinder, it would start & run but die in gear. I reuilt it, now it is as good as gold. As jwb says, great engines"
 
"If these motors are good as g

"If these motors are good as gold, why is everybody having to rebuild them? Too much to go wrong with 3 cylinder,3 carb motor, my opinion."
 
"I'm a commercial fisherma

"I'm a commercial fisherman who's owned 4 mid to late 1970s Johnson/Evinrude 70 hp outboards.I bought my last one 7 years ago which had 80-90 lbs compression at the time,I've gone over 1000 hours with it in all sorts of weather and conditions and have only replaced coils and power packs.These are unquestionably the best motors OMC ever made."
 
Joe ur engine has low compress

Joe ur engine has low compression and it will never idle properly or perform well.

Pull the head off and have a look at the bores etc.

If you decide to rebuild the engine then do the carbies...cause you are on the wrong track at the moment by cleaning them out and retrying the engine.

The 70hp you have is a sweet engine and a joy to rebuild...cheers mate
 
"ok, it looks like a re-build

"ok, it looks like a re-build is in my future. Now, if I can figure out what all that entails... should I focus on just the top end, or a complete teardown / replacement of lower bearings, etc. Also roughly how much $$ are we talking about here?
I bought a used 60hp Johnson vro (early 80's I think) to use in the meantime. I'm in the process of installing it now since it looks like the 70 is kaput for a while."
 
"Re-build the powerhead and a

"Re-build the powerhead and a new drive shaft. Also re-build the carbs.

Also, I thought the shift linkage had something to do with the engine dying while shifting into gear?? Aren't you supposed to troubleshoot the linkage with this problem????"
 
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