Johnson 9.9 hp help please.

[Michael P]

I recently bought a Johnson / Seahorse 9.9 hp motor ( model #10R75C / serial # E4178758). I know that the motor is a '75 year model. Here is what the motor WILL do: Start with ease (four or five pulls), Idel, shift ok. What it WILL NOT do is rev up. When I start the motor and shift it the motor sounds like it is at slightly above an idel when the throttel is twisted to the max. I runs even, (like the proverbial sewing machine) not missing or sputtering. The fuel is mixed correctly, and the gas can and priming bulb are both brand new. <br /><br />The motor was supposedly not run a great deal to begine with...to this end I will say that the under of the hood is cleaner than most new motors the hoses and wires are in immiculate condition, and NO crud whatsoever, the outer physical condition of the motor is aslo very good.<br /><br />When running the motor with the hood off it apperars that the throttle linkage is moving to it full range of motion.<br /><br />Any suggestions would be appreaciated. Taking the motor to a OB mechanic is certinally an option but I thought it might be something simple I am overlooking. <br /><br />Also the air breather on the fuel tank is operating properly and the spark plugs look to be brand new (Champion L77JC4)<br /><br />Thanks <br /><br />WVMike

 

[OBJ]

Re: Johnson 9.9 hp help please.

Hi Mike....<br /><br />Take a look on the starboard side of the carb. You will see the throttle plate shaft coming out the side of the carb body and it will have a pin through it. With the motor not running, shift into forward gear and give the engine full throttle. The pin should be straight up and down. If not, check the cam follower roller. Sits ritht on top of the carb the port side a little.<br /><br />As you start to move the throttle, notice on the cam, which comes out from under the flywheel, a small timing mark. When this mark is in the middle of the roller, the throttle plate should be just opening up.<br /><br />If the roller is good, and from your post the engine has not been run for a while, I would think a carb overhaul is due.<br /><br />Keep us posted....thanks.

 

[rolmops]

Re: Johnson 9.9 hp help please.

Hello<br />You are asking for a small thing you might have overlooked.That is what usually happens to me as well.In this case it sounds as if the fuel makes it to the carburator,but maybe the valve on your tank is almost closed and lets very little air into it.Check all the mechanical parts from your throttle handle to the last little spring on the side of your carburator to see whether the accelleration command actually makes it to the carburator and look inside the barrel to confirm that.If both fuel and command reach the carburator and still no speed your next step would be a carburator cleanup job.<br />good luck.

 

[Michael P]

Re: Johnson 9.9 hp help please.

Thanks for the ideas. After tinkering with the motor I decided to take it to a local dealer and have it looked at. When all was said and done the main problem was a cylinder a little low on compression and the wrong plugs. The mechanic sprayed some "stuff" in to the cylinder and let it set for a while and then took another compression test and it was right up with the other cylinder. With this and the new plugs the motor will start with ease, idel smoothly, AND come up to full RPM. While the cylinder was soaking he took the carburator apart and pronounced it fit as a fiddle. A pressure test of the lower unit and new oil and I am confident that the motor is ready for the upcoming duck season. Again thanks for the help.<br /><br />Mike