Compression Low Compression Question

Scootsbs

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May 28, 2016
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I just bought a 1996 Johnson 150 That has been sitting outside for years. The last registration on the boat is 06' The engine looks like new under the cover and doesn't look like any wrenches have touched it yet my compression is 55 to 65 on all cylinders. I assume this is because of stuck rings from sitting. I got the engine to fire but shut it off imediatlly The question is can I bring the compression back up without re-ringing it.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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welcome aboard.

the answer of your question depends on why the compression is low

if stuck rings - then yes
if worn rings - then no
if rusted and pitted rings - then no

get a bore scope (heck they have them for $20 now that plug into a smart phone) and look at the bores.

FYI - hope you had the muffs on the motor when you fired it up. if not, you toasted the water pump
 

ondarvr

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When all cylinders come in that close and low, I always check to see if the gauge works correctly, they are often wrong, sometimes by a significant amount.
 
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James R

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I agree with ondarvr. The good comps on these motor are around 90PSI. Before doing anything else try shooting a 1;1 mix of Marvel Mystery oil and two stroke oil into the plug holes and blip the motor over and let it soak overnight. Check the comps next day. If no improvement you will need to pull the heads to check, Works for me.
 

flyingscott

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Need a model # is it a looper or crossflow big difference in the compression of those 2 motors.
 

flyingscott

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Then good compression is 110+ definitely double check the compression. 90#s of compression would be to low and still need a model# to be sure.
 
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James R

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I may be wrong but I think this is a 60* motor. I have rebuilt two of these and the compressions were 90PSI. My gauge is used on a weekly basis and has always provided accurate readings and checked against other pressure gauges. These motors are smooth, quiet and powerful. If it comes up you may have a winner.
 

flyingscott

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Unless the saltwater motors are different then the Venom and Intruder models. I have always been higher on the loopers than the crossflow usually goes up after the break in.
 
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Scootsbs

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May 28, 2016
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Thank you for posting replies' Model is J150ELEDO. I am very confident in my compression guage its an expensive one and well taken care of. I can see if I can find one to rent at the parts store to confirm. I was able to fire it up today and it ran pretty rough but on its own. this was using the gas that was in the boat that is I don't know how old. I used the seafoam on it and have not checked the compression yet to see if it has changed but will tomorrow. I have a lot to learn on this engine as all of the outboards i have ever owned have been older and simpler. YES on the muffs.
 
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James R

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If it is sticking rings Sea foam will do very little for you. If you insist on using some proprietary stuff try Yamaha Ring Free. Dont use suspect fuel especially out of an old possibly dirty tank. You can cause more damage. I would use a 50:1 mix from a clean jug or tank in case the oiling is not working. Got to baby this thing if you want it to come back. It should run on the Muffs ok but it will be lumpy because it needs the back pressure on the exhaust that the water in the pond provides to run correctly. A barrel will suffice.
 

boobie

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To free up stuck rings get some BRP Engine Tuner and follow the directions on the can. Been using it for 20 years and had good luck.
 
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