Throttle spring on 1981 Mercruiser 120. Courting disaster

[Mike Lukacevic]

The other day I had my new to me boat on the Ohio river. Hit some major waves and the throttle went wide open. The boat nearly went out of control. Obviously, the tension of the spring pulled it there. Why the hell is this thing installed.
On my set up, it looks like original. I had misgivings when I was working on it, it seemed counterintuitive.
Why is this spring on there to begin with?
At the very least, it should be there to pull it back to idle.

Any ideas? Is it necessary to have it?

 

[nola mike]

What carb do you have? How is the throttle opening with the cable holding it closed?

 

[Mike Lukacevic]

What carb do you have? How is the throttle opening with the cable holding it closed?

Rochester 2 jet. It’s just the installation of the return spring. It’s original and on backwards. The problem I’m running into is instead of its original purpose, like on a car, to return to idle, it pulls it to wot. I’m surprised I didn’t swamp the boat. I’ve been boating for over 50 years but my first I/o. I’m going to have to manufacture another point to attach the spring in the opposite tension direction. Is that spring totally necessary? Zero idea. But it’s not going back on if I can’t figure a work around. That’s for sure. Was life threatening.

 

[stresspoint]

i believe there is no way the throttle can go to WOT unless the cable breaks close to the carb or cable falls off the ball on the carb lever.
? what am i missing here ?? , as the spring you speak of is designed to pull the butterfly's to shut if either of the above happens.

pics of what you are facing may help to understand what went amiss ,

 

[Scott06]

Rochester 2 jet. It’s just the installation of the return spring. It’s original and on backwards. The problem I’m running into is instead of its original purpose, like on a car, to return to idle, it pulls it to wot. I’m surprised I didn’t swamp the boat. I’ve been boating for over 50 years but my first I/o. I’m going to have to manufacture another point to attach the spring in the opposite tension direction. Is that spring totally necessary? Zero idea. But it’s not going back on if I can’t figure a work around. That’s for sure. Was life threatening.

post a picture of what you have. Some of the Mercs use throttle return springs in case the cable breaks but most do not. here is an example in a cut sheet of a 357 alpha. But it should close the throttle not open it

To to mercruiser parts .com or marine engine .com and put your serial number in to see what is there from factory

 

[Mike Lukacevic]

i believe there is no way the throttle can go to WOT unless the cable breaks close to the carb or cable falls off the ball on the carb lever.
? what am i missing here ?? , as the spring you speak of is designed to pull the butterfly's to shut if either of the above happens.

pics of what you are facing may help to understand what went amiss ,

I will in just a bit.

 

[Mike Lukacevic]

post a picture of what you have. Some of the Mercs use throttle return springs in case the cable breaks but most do not. here is an example in a cut sheet of a 357 alpha. But it should close the throttle not open it

To to mercruiser parts .com or marine engine .com and put your serial number in to see what is there from factory

This diagram is correct. BUT it pulls it wot.
I ducked around just now to reverse the tension. But who wants to have to keep your hand on the throttle the whole day while fishing?

Imagine if on your old car (in my case an MGB)
You would switch the direction of the return spring 180 degrees. That’s what I’ve got going on here. I cannot imagine the previous owners of the last 40 years not noticing this.
I will tell you that it is installed to spec with all the original parts. It’s just wrong. I’ll get picks and video poste haste. The spring is off now and I’m not gonna get killed on this thing…because of this. MYbe something else

Addendum: in my particular case. The throttle cable “pulls” the butterflies open rather than pushes them. This seems to be the original installation

 

[Bt Doctur]

all PULL the throttle and use a spring to CLOSE the throttle in case of a cable failure.try around the thermostst housing bolts, with a longer spring ot the rear carb nuts with a metal extention

 

[snowbrd84]

The spring does pull forward, but its on the bottom of lever, which rotates the top back to the idle adjustment screw to close. If it is hooked up to the top and pulling away from the idle screw, then someone hooked it up wrong.

 

[stresspoint]

This diagram is correct. BUT it pulls it wot.
I ducked around just now to reverse the tension. But who wants to have to keep your hand on the throttle the whole day while fishing?

Imagine if on your old car (in my case an MGB)
You would switch the direction of the return spring 180 degrees. That’s what I’ve got going on here. I cannot imagine the previous owners of the last 40 years not noticing this.
I will tell you that it is installed to spec with all the original parts. It’s just wrong. I’ll get picks and video poste haste. The spring is off now and I’m not gonna get killed on this thing…because of this. MYbe something else

Addendum: in my particular case. The throttle cable “pulls” the butterflies open rather than pushes them. This seems to be the original installation

when the spring is hooked up correctly there is not enough tension on the throttle lever on the carb to pull the control lever back to idle , so you do not have to hold the lever all day when riding.
.
the spring is a safe guard if something breaks to stop the motor goin WOT as yours did.

the only way i can see that it pulled WOT is if the cable fell off and the spring was hooked up wrong !.
so with that said , you need to look for an underlying problem , running without that spring correctly placed will be a danger should the cable break or the ball end snaps.

 

[Mike Lukacevic]

The first photo is the throttle at idle and the direction of the spring. The second is the throttle at wot.
When the boat was built I’m sure this is the way it was installed. Probably the original return spring. It returns alright. Into wot.

I did not want to go to the trouble of reconnecting he spring. Suffice to say, the attachment points are original. Just the way they had to do it when it was built. Thanks for the replies

 

[Bondo]

Ayuh,..... That is Not original,.....

Boat throttles really don't need any spring, at all,.....
The throttle cable should, when adjusted correctly, put a slight tension on the linkage to hold it tight against the idle adjustment screw,.....
It shouldn't need a return to idle spring,.... 'n differently Not a spring pulling it to Wot,.....

 

[snowbrd84]

I wouldn't be surprised if the throttle cable has stretched, and someone rigged that up to get it to both seat against the idle screw and then pull all the way to WOT in the other direction. When the cable stretches enough, you can only achieve one of those things, and it's time for a new cable, not a spring to try and compensate.

 

[stresspoint]

+1 , that spring should not be there , there should be ""no spring at all""" on your set up.

the only spring that should ever be on a throttle / carb linkage should be to pull the carb butterfly's to "closed " position.

 

[Scott06]

The first photo is the throttle at idle and the direction of the spring. The second is the throttle at wot.
When the boat was built I’m sure this is the way it was installed. Probably the original return spring. It returns alright. Into wot.

I did not want to go to the trouble of reconnecting he spring. Suffice to say, the attachment points are original. Just the way they had to do it when it was built. Thanks for the replies
View attachment 388412

what is with all the tape around the adjustment barrel nut? willing to bet that is part of the issue. def there should be no spring to hold it open....