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rock44

70 hp johnson outboard wont go full speed

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How did your mechanic determine you had internal damage from overheating ? As posted if the compression is good the engine is potentially salvagable !Do you known that the engine was overheated ? Commonest causes are a blocked intake , usually from a plastic bag blocking the intake or an impeller that was not changed at a regular interval which would disintegrate and pieces would block the water passages ! The wrist pins on the pistons would go or the needle bearings on the crankshaft would go ! Turning the motor by hand may give an audible sound , then it is probably " game over " ! If not it should start then there would be no doubt with the knocking sound !

Again how id your mechanic decide that you had internal damage  ?

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He said he sprayed  ether on block while it was running and it sucked it in and motor stopped. So a vacuum leak is apparent there. That would mean its a gasket or seal where the blocks come together  i believe 

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Why would you spray either on the block ? Spraying either on the spark plugs , into the combustion chambers and throats of the carbs may give some indication that the problem is fuel if the engine does start momentarily and  not electrical !

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Yes I know it overheated.  My alarm was going off for a while to get back in to shore. That being said. U can see that the motor got so hot it melted plastic connections  on some of the wires laying on the topic the motor.  And the seam where the block meets the intake has apparent  melted paint. I am getting a second  opinon Thursday from  the johnson dealer. Ill get back to you guys then. At this point ive started to look at used motors in case the motor needs an overhaul for sure and its over my head in diy or cost . Well see . Thanks everyone 

Edited by Tim G.

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Your initial post did not mention the obvious problem of overheated motor ! your mechanic is correct the engine is probably ruined , cut your losses and move on ! I would guess the cause was the impeller [ water pump ] which is a service item .

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After cleaning the carbs several times on my old 86 70hp VRO and getting nowhere I decided to pitch the VRO and bought a fuel pump on craigs list for about $80.

Problem solved! installed in less than 15 minutes , now I just need to remember to mix my gas.

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I finally  got my answer to the overheated engine. I took the head off to inspect the pistons and the sleeve  on cylinder 2 has twisted . I was  told by the dealer that the block is now junk.  I've already  got another motor installed on the boat this weekend . Thanks for everyone's help. As I said before I was hoping for good news but this is by the worst case scenario  

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Thanks for the " post mortem " [ often we do not get an answer on the cause of the problem ! ] . Question remains why did the engine overheat in the first place ? If you buy a used engine the impeller can be a service item IMO .

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Impeller is a SERVICE item ! Like the FRAM commercial of years gone by " pay me now are pay me later " [ later is usually a LOT more !

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