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150hp Johnson fast strike dies after about 5 seconds

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Bowenlhzn

Member
I have a Johnson 150 fast strike. Recently I was having a problem where it wouldn’t get about about 3000 rpm while in the water. I took the head off and found that I had scored cylinders. I took it to a shop and got it bored out and then I rebuilt the motor with .020 oversized pistons since that’s what it was bored out. After I rebuilt the motor it started right up and ran without any problems for about 45 minutes I just had it idling to try to break it in. After about 45 minutes it started to miss every once in a while and it died. Now the motor will start and it will only run for about 5 seconds and then it stalls. I noticed that the carbs have a milky white substance in the carburetor throats. I changed the gas and then took a sample of the gas entering the motor and it didn’t have any water. I checked the compression and they were all about 100psi when warmed up. And between 100 and 110 when cold. Would the 10psi cause a problem? I haven’t taken the heads off to look for any scoring again. Is there any other explanation for this problem?
 
Did you determine how / what scored the cylinders.------Replaced water pump impeller ?---Mixing gas and oil at 25:1 for break-in ?----Oil injection in service and oil out put tested ?
 
I believe that the cylinder got scored initially because my dad ran it one time without putting oil in it, after that it didn’t run right and progressively got worse until I fixed it. I did mix gas 25:1 on break in.
 
racerone said:
Did you determine how / what scored the cylinders.------Replaced water pump impeller ?---Mixing gas and oil at 25:1 for break-in ?----Oil injection in service and oil out put tested ?
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I believe that the cylinder got scored initially because my dad ran it one time without putting oil in it, after that it didn’t run right and progressively got worse until I fixed it. I did mix gas 25:1 on break in. The oil injection was taken out previously and we have been premixing it with the gas.
 
I just took off the cylinder head and there is no scoring that I can see or feel. I do however notice that the gas/oil mixture in the cylinder is still very milky white. I think that this has to be the problem, but I’m not sure where water would be mixing with the gas. There is good gas coming into the motor but the gas in the carburetor and cylinder is milky white.
 
Was the block pressure tested before boring? Sound like a glue line failure..most likely what caused original failure. Usually it leaks in #1 or #3 but have had it leak in all cylinder's
 
faztbullet said:
Was the block pressure tested before boring? Sound like a glue line failure..most likely what caused original failure. Usually it leaks in #1 or #3 but have had it leak in all cylinder's
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the original pressure was about 100psi on cylinders 1,2,3,5 and 80 psi on cylinders 4,6
 
No.....the water passages pressure tested, This block is made up from pieces of Styrofoam glued together, The glue line are known to leak from age and heating cycles. Then they start weep water into cylinders causing steam cleaning, cylinder scuffing knocking,missing , I suspect that what took out original failed cylinder as lack of oil usually shows on all cylinders
 
faztbullet said:
No.....the water passages pressure tested, This block is made up from pieces of Styrofoam glued together, The glue line are known to leak from age and heating cycles. Then they start weep water into cylinders causing steam cleaning, cylinder scuffing knocking,missing , I suspect that what took out original failed cylinder as lack of oil usually shows on all cylinders
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would that mean I would have to scrap the whole block then?
 
If that's where water is coming from yes as to expensive to repair...sleeve has to be pulled,block welded and machined and sleeve reinstalled.
 
Ok,ya got this milky crap on#2,4,&6.that wont make it die in 5seconds. Is this white stuff on spark plugs? Are ALL throttle plates closed? Any sighn of this white stuff on #1,3,5?
 
I read where you got fresh gas. Have you drained carbs,vst,hoses so that your running on fresh gas thzt you have checked for water.
If you did get a slug of gaswater,motor has not run long enough to clear system.
 
Rwbutler said:
I read where you got fresh gas. Have you drained carbs,vst,hoses so that your running on fresh gas thzt you have checked for water.
If you did get a slug of gaswater,motor has not run long enough to clear system.
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i have not drained the carbs yet, I will do that today and retry. I didn’t take the cylinder head off of 1,3,5 but I do see milky gas in the carburetors for cylinder 1,3,5
 
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