140 Johnson V4 O/B loses speed then shakes

[kennethjsteele]

I have a 1994 Johnson O/B V4. After about 10-15 min going about 25 the motor will lose power as if I put it in neutral. Then if I try to go over 10mph the motor shakes. After a few min going slow I can get back up to 25 with no shaking. Any suggestions?

 

[mckee1787]

Re: 140 Johnson V4 O/B loses speed then shakes

Check your throttle cable for stretch and also your tension knob on you control. Sometimes when bouncing around the throttle can work its way back.

 

[kennethjsteele]

Re: 140 Johnson V4 O/B loses speed then shakes

The throttle lever stays forward. Also how do you explain the engine shaking after I start moving again?

 

[daselbee]

Re: 140 Johnson V4 O/B loses speed then shakes

You will have to double check this to be sure, but it sounds like S.L.O.W. mode is kicking in. The V6s in your year range have S.L.O.W. mode, which limits RPM when the engine overheats.
The RPM is limited to 2500, and the engine shakes badly.

Now, the question is, do you have S.L.O.W. mode on your '94 140. I would bet so, but I don't know for sure.

What does your OMC original manual say?

 

[kennethjsteele]

Re: 140 Johnson V4 O/B loses speed then shakes

I will look at the manual tonight. If it is going into slow mode what would cause it to do that? Do you think an electrial issue would cause it to overheat?

 

[Chris1956]

Re: 140 Johnson V4 O/B loses speed then shakes

I believe activation of the SLOW system would be caused by an overheat. I recommend you put your hand on the heads and see if they are hot. They should run at 140*, which you can keep your hand on for several seconds.
That motor has two thermostats. Perhaps one or both are bad, or the impeller needs changing.

 

[ezeke]

Re: 140 Johnson V4 O/B loses speed then shakes

The only thing that can cause your motor to go into S.L.O.W. mode is overheating. Your symptoms are those expected when S.L.O.W. is activated.

Slow activates at 203 degrees F., so when it does activate, you should not run the motor until you correct the condition that is causing the problem.

 

[another todd]

Re: 140 Johnson V4 O/B loses speed then shakes

Fuel restriction? Plugged filter?

 

[ezeke]

Re: 140 Johnson V4 O/B loses speed then shakes

Fuel restriction? Plugged filter?

You really should read your service manual once in a while; 1995 factory service manual #503152 see page 3-23, line 8: "The S.L.O.W. warning system is isolated from other warning horn signals by a blocking diode in the engine wiring harness."

 

[kennethjsteele]

Re: 140 Johnson V4 O/B loses speed then shakes

Had more problems the next time we had it out we couldn't get the motor to run for more than a few seconds unless we used the bulb. Even then it wouldn't stay running. We just replaced the fuel filter that didn't fix it. We replaced the fuel pump www.usavemarine.com for $322.00. The motor fired up and ran forever after that. We are putting it in the water tomorrow. We'll see if the new pump fixes the SLOW mode issue.