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ballen06

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I have a 2 cycle Yamaha 150 hp outboard

It was running perfectly . Then out of the blue it started running rough.

So I pulled the spark plugs and they were oily... so I bought new ones and installed them.

I still have the same issue... so...

I checked the gas fuel filter on the motor and it was clear.

I checked the diaphragm on the fuel pump... looked fine.

Is there any type of diagnostic test I could perform?

Help me please.
 
Last edited:
Docksidemarineservices said:
When you squeeze the primer ball does it get firm and stay firm?
Click to expand...

Thanks for your response..

Yes it does.. I squeezed it a few more times and the motor cranked right up...

but still running very rough .. smoking more than normal... when I took it to idle rpm it died... (it will not start at idle rpm)

Then I restarted it and it was really smoking let it run for a bit .. took it down to idle rpm and it didn't shut off!..Crazy.

Anyway .. the problem persists .. motor is really running rough... and smoking more than normal.
 
ballen06 said:
Thanks for your response..

Yes it does.. I squeezed it a few more times and the motor cranked right up...

but still running very rough .. smoking more than normal... when I took it to idle rpm it died... (it will not start at idle rpm)

Then I restarted it and it was really smoking let it run for a bit .. took it down to idle rpm and it didn't shut off!..Crazy.

Anyway .. the problem persists .. motor is really running rough... and smoking more than normal.
Click to expand...


Clarity .. Of course it didn't shut off at idle .. it ran at a higher rpm and ran rough at that point I just turned the ignition off at that point.
 
Not clear here. I think that Docksidemarineservices is asking is, without the engine running, when you squeeze the primer ball, does it get hard and stay hard, or, does it get soft again without the engine running.
 
Start wih the basics, compression should be even on all cylinders at around 120psi, check for spark on all cylinders.
 
Latest info...

Checked the spark on all cylinders.. they all sparked.

Latest news is the engine seems to run OK with the cowl off... but when the cowl is on it won't even idle.

Also the idle screw doesn't seem to have much of an affect on the idle.

That's all I have right now.
 
Not familiar with your model but sounds like possible exhaust leak or maybe engine breather pipe split / disconnected, allowing fumes into air intake. Also piston blowby due to low compressions/worn rings. When cowl is off pure air is getting to cylinders.
 
See if it runs okay out on the water with the cowl off, if it does then you have probably got a blown or leaking power head gasket allowing exhaust gasses to leak up into the cowl in which case you will have to remove the power head.
 
ballen06 said:
Latest info...

Checked the spark on all cylinders.. they all sparked.

Latest news is the engine seems to run OK with the cowl off... but when the cowl is on it won't even idle.

Also the idle screw doesn't seem to have much of an affect on the idle.

That's all I have right now.
Click to expand...

Run the engine with the cover off after the sun goes down. Get a spray bottle full of water and spray the spark plug wires while it is running. Do you see a lightning storm? If yes, you need new wires.

They can arc to the engine cover.
 
It's confirmed.. There was a hole in the exhaust port which allowed fumes to come up under the engine cover. The motor doesn't like breathing these fumes.
 
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