compression test question, 1989 150hp johnson

[crabbydad]

I did a compression check on a 1989 150 VRO Johnson on a 19' grady tournament. on 5 of the cylinders the needle pulsed at each compression stroke, and settled on 90 psi. the number 3 cylinder went right to 85 psi, but did not pulse at each stoke of the piston. What does that mean? Also when I ran the engine, it had a "cough". the engine wasn't warmed up, I was checking the engine with the owners permission, before he arrived. there was also a dark oil coming out of the rectangular openings on both sides of the lower unit where the water runs out. the owner had run the motor that morning.
thanks for any information

 

[boobie]

The dark oil is unburned fuel which is normal.

 

[SparkieBoat]

85 -90 normal on those motors, you could try a decarb to get compression up some.

 

[crabbydad]

I bought that boat today for 2800. I rechecked the compression today when I got it home. 5 cylinders 90 psi and the #3 is 80 psi. is that too much variation? the motor was cold, I don't think it had been run since I checked it out last Saturday

 

[SparkieBoat]

%10 is the max recommended. try to do a decarb. maybe it will get that compression up.

 

[JonathanMJ]

Seafoam it, spray a small amount of oil in the cylinders and re-check. Bumped my weak cylinder up to 94 on my '57.

 

[crabbydad]

just bought some seafoam and of course it just started raining. I'm going to spray it in the intake until it stalls, then spray in each cylinder and tilt it up and let it sit all night- if it stops raining.

 

[SparkieBoat]

get the motor hot then remove the plugs and spray seafoam in there. then get a 1 gallon portable tank mixed with 2 stroke oil at 50:1. and dump a pint of seafoam in it. run it down the river adjusting your throttle up and down. it will smoke a lot

 

[crabbydad]

I warmed the boat up and sprayed into the carbs, 3/4 of a can until it almost stalled. shut it off, pulled the motor up, removed the plugs, sprayed in cylinders than rotated motor by hand ,sprayed a little more and put the plugs back in loosely. i'll let it sit all night and in the morning turn it over by hand a few times with the plugs out, then reinstall plugs and smoke out the neighborhood. there was a lot of smoke just from what I sprayed in the carbs. I can imagine what it will look like tomorrow. hopefully this will bring the compression up in the weak cylinder.

 

[JonathanMJ]

How did it turn out?

 

[emdsapmgr]

When an engine just starts cold, it is running on a lean mixture. That's why it needs a choke system-to richen up the fuel mixture for cold starting. When still cold, the engine may sneeze, an indication of lean running. For the first minute or so of the cold-start cycle, you may need to occasionally push in on the key switch to squirt extra fuel (choke) in the carbs. After a minute or two, the engine should warm up full and should idle normally. If the engine still coughs when fully warmed up-that may be a "lean sneeze." That's a different problem. Possible that the idle air passages in the carbs may be restricted and cause a constant lean idle condition. That usually is resolved with carb overhauls.

 

[crabbydad]

ran the motor until most of the white smoke was gone. did a compression check. didn't really make much of a difference. the low cylinder is a little over 80psi, but the motor does seem to run good after warming up a minute or so.

 

[emdsapmgr]

It's not illegal to do a second round of combustion chamber cleaning.....

 

[SparkieBoat]

try it the way I described in post 8.

 

[crabbydad]

I may do that when I'm ready to put the boat in the water. I just bought it a couple days ago

 

[JonathanMJ]

DO IT! DO IT NOW!!! lol We mechanical theorists can get a bit pushy sometimes. Just started a new boat project myself. Best of luck. Watch your tell tale for steam in the meantime. Very helpful for determining head leaks, water pump health, and lean situations. Holler if you get some more info. -Jonathan