engine racing at idle

[tchappell]

I have an '86 Johnson 40 VRO which continues to operate at a very high rpm even after the throtle has been shifted to neutral. I've checked the operation of the linkage and all seems to be fine. I disconnected the fuel primer solenoid hoping that it was sticking but it made no difference. When I shut off the engine and restart it, it operates normally at idle. I can even increase the throtle to a point and bring it back to idle without causing the problem. But, once I pass a particular point (don't know at what rpm it happens) the engine sounds as if it is at WOT and will not return to idle. Any ideas?

 

[Dhadley]

Re: engine racing at idle

Is this in the water or on land on the flushette?

 

[CATransplant]

Re: engine racing at idle

Sounds like something is binding somewhere in the linkage, assuming that this is happening in the water, on a boat, and not with the earmuffs.<br /><br />If it's on the muffs, stop doing what you're doing. Revving two-stroke engines with no load is a recipe for disaster.

 

[tchappell]

Re: engine racing at idle

Both, in the water or on land.

 

[Dhadley]

Re: engine racing at idle

If you rev it high enough with no load as CAT mentioned, it will run away. <br /><br />Does this only happen in neutral?

 

[tchappell]

Re: engine racing at idle

Yes, it happens in neutral when I manually advance the throtle linkage. It happens in gear, in or out of the water. Haven't tried manually advancing the throtle when in neutral and in the water. This problem started at the end of the day as we were approaching port. We had been about 12 miles down the coast in the Gulf scalloping and had no problem until the last mile of the return trip. When the engine ran away as I was attempting to stop, I turned off the ignition. I then restarted and was able to continue as long as I didn't go over a particular rpm. Again, I don't know what that rpm was, but I would say that we were at about 1/2 speed or less just based on the feel of things. I just remembered that on one of the occasions where the engine ran away, turning the ignition off didn't immediately cause the engine to stop. I was a little worried until it finally shut down after what seemed to be an eternity.

 

[Dhadley]

Re: engine racing at idle

Heres what will happen -- if the load on the motor suddenly disappears the motor will run away. At some point shutting off the key has no effect. You have to turn the key back on and flood it with the primer. <br /><br />There are a couple of situations that cause the motor to have no load. One is for the prop hub to spin. That may be whats happening. At half throttle the hub spins and the motor revs. Bringing the throttle back has no effect. Once you get it shut off the hub hooks up again and youre OK until it slips again.<br /><br />Another situation is for the driveshaft splines to strip. Most likely when that happens they never lock up again. <br /><br />If you try to duplicate the situation in neutral you can rev it to the point that it runs away.

 

[tchappell]

Re: engine racing at idle

That makes a lot of sense! And, I think that is probably the problem considering the situation in the Gulf. The motor is on a pontoon boat which is why I am told that the prop is continually being fouled by grass since the pontoons funnel the grass and whatever else directly to the prop. There were countless times that the engine would run away indicating that the prop was fouled with grass. I would immediately put the motor in neutral and then in reverse to remove the grass. At that point, we would continue till the next batch of grass fouled the prop. Now that you have said what you did about the prop hub spinning, it is all beginning to make more sense. I doubt that the driveshaft splines have stripped since I was able to make it back to the dock under my own power. <br /><br />I certainly appreciate your help and will check into the prop/hub situation as soon as it stops raining. Hope Katrina doesn't turn back into your area. Good Luck!

 

[Dhadley]

Re: engine racing at idle

Yeah, we're hoping she'll leave us alone too!<br /><br />Let us know how you make out! Good luck !