1999 50 HP Johnson will only run 2250 RPM at full throttle

[BediasJim]

I have a 1999 50 HP 2 stroke Johnson that will not run over 2250 RPM at full throttle. I verified that the carburetor butterflies are at full open position,
squeezing the bulb does not help. It idles and runs smoothly but will not come up to speed. Anyone else have this problem and solved it?

 

[kmcgillis]

Re: 1999 50 HP Johnson will only run 2250 RPM at full throttle

If it has a SLOW system which I think it does that could be your problem. You need to check your temp sensors and system. This would limit your motor to about 2500 RPMs if it bad. Basicly it keeps your engine from running too high if it over heats.

 

[BediasJim]

Re: 1999 50 HP Johnson will only run 2250 RPM at full throttle

This model has two carburetors and does not have fuel or oil injection. I have to mix the oil into the gas .(1 qt. to 10 gallons) I don't see any electronics packages that would initiate this SLOW function. Thank You - Jim

 

[jonesg]

Re: 1999 50 HP Johnson will only run 2250 RPM at full throttle

SLOW is switched within the power pack, the temp sensor sends a signal when it closes to ground.
Test temp sensor by disconnecting and running it.

 

[tashasdaddy]

Re: 1999 50 HP Johnson will only run 2250 RPM at full throttle

slide the cover back on the temp sensor wire, there is a sizzor connector there, disconnect it and see if it will run. if so replace sensor.

 

[BediasJim]

Re: 1999 50 HP Johnson will only run 2250 RPM at full throttle

Any suggestions as to where the sensor might be located? The SELOC manual says it is either atan wire or a tan/blue

 

[countvlad]

Re: 1999 50 HP Johnson will only run 2250 RPM at full throttle

Any suggestions as to where the sensor might be located? The SELOC manual says it is either atan wire or a tan/blue

look on the heads... cant be hard to find .. its probably right n front of you once you take the mototr cover off...

 

[Silvertip]

Re: 1999 50 HP Johnson will only run 2250 RPM at full throttle

Tan wire going to the temp sensor on the cylinder head.

 

[BediasJim]

Re: 1999 50 HP Johnson will only run 2250 RPM at full throttle

Found the sensor on sparkplug end. It has a tan/blue wire on it which is a higher temperature (234-246 tan/blue) (197-209 tan) deg. F. There is a 5/8" nut that holds the sensor in place. When you loosen the nut, you see the tan/blue wire going through a rubber grommet. I'm hesitant to pry this grommet out as the sensors are $92.00 each. Any ideas how to remove it safely? I was going to test it in hot oil, but I think I'll wait to see how the test comes out with the sensor disconnected. At ambient temperatuure the sensor shows open.
I put the lower unit in a 35 gallon garbage can filled with water today. The water pump put a full stream of water so I think the water pump is OK. I would appreciate any insight you might have