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Help Identify year and model of Johnson outboard 15 hp

lywtrte

New member
Hi I have a Johnson outboard 15 hp with the logo Seahorse MagFlash CD. This unit was repainted and the equipment tag was missing.
It has the following features
1. Use Power Unit for ignition
2. Has older carburetor all metal not the one that have black plastic top
3. It has a pee hole for water pump function indicator.

Would appreciate information on year or range of years and model number if known

This motor has a problem running at high speed. The unit run when cold and died when engine warms up. It can run again if choke is partially open at a certain spot. The carburetor has been cleaned and replaced with new float, needle and plug. I saw a post of a similar engine with similar problem where the owner changed the crankshaft seal. Could some one explain why crank shaft seal seems to fix carburetor problem? I want to try the same fix but dont know the model to order the seal. If you know the partnumber for the crank shaft seal please let me know. Should the lower crank shaft seal to be replace as well? is lower seal harder to replace?

Many thanks
 
Post some pictures.------Your motor is a 2 stroke style engine.-----It is a 2 stage air processing machine.------If a crankshaft seal is bad ( doubt it on yours ) then air would leak out of the crankcase.----That means fresh fuel / oil / and air is not transferred in the engine.------Hope this helps , but perhaps you are now really confused too.
 
Post some pictures.------Your motor is a 2 stroke style engine.-----It is a 2 stage air processing machine.------If a crankshaft seal is bad ( doubt it on yours ) then air would leak out of the crankcase.----That means fresh fuel / oil / and air is not transferred in the engine.------Hope this helps , but perhaps you are now really confused too.


Thanks for the reply. I think I understand the explanation. I did not realize that the 2 stoke use air in the engine compartment to burn. Would you explain why you doubt it is on my engine? I a have done all the carburetor cleaning and ran out of idea on what to do next to improve the HS performance.

I have uploaded 4 pictures showing my motor. Hope this can help identify the model.
 

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That looks to be about a 78 / 79 model.------The white paint may mean that motor overheated.----Start with a compression test.----Post your numbers.----Air does not burn " in the engine compartment " it is first compressed in the crankcase before it is transferred to the cylinder and compressed again.----When you understand how your motor works it will be so much easier to operate and repair it.
 
That looks to be about a 78 / 79 model.------The white paint may mean that motor overheated.----Start with a compression test.----Post your numbers.----Air does not burn " in the engine compartment " it is first compressed in the crankcase before it is transferred to the cylinder and compressed again.----When you understand how your motor works it will be so much easier to operate and repair it.

Great years 78 and 79 is close together so the part should work for either year. I will pickup a compression gauge and do the test and post the number.

Thanks
 
I bought a compression tester from Harbor Freight and did the compression test. The values are 43 PSI on upper cylinder and 45 psi on lower cylinder. This seem low yet the engine is able to run. I wonder is my gauge is not good. I will have to do a gauge comparison to see if that might be the issue but these number seem low to me. If the pressure values are true, does this mean I have to change the rings? are there anything else I can do to bring this number up?

Thanks
 
----I usually see 90 PSI on these motors.-----Remove cylinder head to inspect this machine.----Could be a blown head gasket.-----As I clearly stated the " paint work " appears to be done to cover up discolored paint from overheating !!!
 
Racerone, Thanks for helping me on this issue.

90 PSI is a long way from my 45 psi compression so definitely something is going on there. I was surprise to see see the compression this low yet the motor seems to run ok other than it cannot run in HS for extended time. I thought low compression would make starting engine difficulty but this engine can start with 2-3 pulls of the rope.

About overheating, I think the paint might have been a false sign. The flaking off of the paint is likely poor paint job. The whole engine was repainted and the blistering paint surface was of the new paint coat. the original paint seems ok. However, If the engine was overheated, what would this mean ? I think the water pump is running fine as there are water coming out of the pee hole and also on the exhaust hole. Is there thing I must do to repair an overheated engine?

Before I open the cylinder head can you help answer some questions below:
1. Do I need to order the replacement head gasket or can I reuse the head gasket with gasket sealant?
2. If the head gasket is blown, should there be physical sign on the outside of the headgasket like oil stain or heat marks as the compressed gas escape?
3. What do i look for when open up the cylinder head to know if it was a blown gasket?
4. I am sure I will see carbon deposit inside the combustion chamber, should I clean these up? what kind of chemical or technique should I use to not damage the pistons and rings?
5. If the head gasket is not blown and the problem was related to ring and cylinder fit-up, is there anything I can do to fix the problem temporarily to keep the engine running for the summer and do the major rebuild during the winter?
6. Is cylinder head removal an easy thing to do ? how much time to take it disassemble and reassemble?

Thanks
 
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