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1983 Johnson V4 140 Low Compression

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RMedus

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I have low compression on all 4 cylinders 82-89 PSI. I am assuming I need the power head rebuilt unless anyone has a suggestion to get the old girl back up and running. This is a project boat for me, the wife and our service dog to go cruising in. Too old for waterskiing...LOL. This is on a 1983 Renken bow rider. We took it out this morning and couldn't get up on plane. I am a retired Jet Engine Mechanic and not used to outboard engines.
 
Head gaskets are cheap.-----Remove one cylinder head and have a look in there.-----These motors are famous for broken piston rings.-----Then again it could have plugged carburetors.----Or lost spark on 2 cylinders.-----Linkage fallen off. ETC.-----How did it run for you last season?----Could be a bad compression gauge as well.----All so easy to check out.
 
Just bought the boat in March, Spent time restoring it, Motor sounds great on a hose but not so much when on the water. Brand new compression gauge. Rebuilt the Carburetors. The boat had set for 8 years. Wishing I had an air conditioned shop to work on it in right now.
 
You might go to Napa Auto Parts, AutoZone, any local parts store and ask them about the "Borrow a Tool" program.
My compression tester was reading 90psi.
I borrowed one from a couple stores and I got 120 with theirs.
.
 
And it doesn't matter if it's a brand new compression tester, you need one with a Schrader valve at the piece that screws into the spark plug hole.
 
I just acquired an abandoned Bass Boat with a Johnson 120hp on it. I got the motor to start, gonna check it out as a possible replacement for the 140. would rather have the 140 but 20 hp isn't that big of difference. Hopefully it is in better shape.
 
Autozone guage read from 115 to 122 psi. I will be returning the guage I bought.
Now to figure out why she isn't running good on the water.
 
racerone said:
Head gaskets are cheap.-----Remove one cylinder head and have a look in there.-----These motors are famous for broken piston rings.-----Then again it could have plugged carburetors.----Or lost spark on 2 cylinders.-----Linkage fallen off. ETC.-----How did it run for you last season?----Could be a bad compression gauge as well.----All so easy to check out.
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What could cause lost spark on 2 cylinders? Being an old auto mechanic of the shade tree variety, I had an induction timing light and checked each wire, all were firing with one slightly intermittent. Previously I had no spark on 2 cylinders and replaced 2 coils and it did seem to improve. (on the hose that is). On the water was a different story. Was able to keep her running at about 2200 - 2400 RPM but any advancement on the throttle she would bog down. that was the second trip to the lake, the first trip she wouldn't even idle long enough to put in gear.
 
RMedus said:
What could cause lost spark on 2 cylinders? Being an old auto mechanic of the shade tree variety, I had an induction timing light and checked each wire, all were firing with one slightly intermittent. Previously I had no spark on 2 cylinders and replaced 2 coils and it did seem to improve. (on the hose that is). On the water was a different story. Was able to keep her running at about 2200 - 2400 RPM but any advancement on the throttle she would bog down. that was the second trip to the lake, the first trip she wouldn't even idle long enough to put in gear.
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What spark plugs are you using? You should be running surface gap Champion QL16V Spark Plugs.

Follow the CDI Electronics Troubleshooting Guide to diagnose your spark condition. This will tell you every part and step to follow. Also, spark needs to be tested using an air gap tester set at 7/16" gap.

The bogging when you advance the throttle sounds like the timer base is sticking and not allowing the timing advance to work. After setting for 8 years this is very possible. You might need to remove the flywheel and investigate.
 
RMedus said:
Bookmarked and will see what I can see. Thank You BUNCHES!!
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If you've worked on Jet engines using precision tools, then you can work on this outboard. Just follow the CDI steps point by point and it will either confirm your ignition system is good, or will tell which component (s) is bad.
 
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