Fast Idle after throttle reduction

[rickturl]

I have a 1990 AS Volante with the 351 carbureted engine and no electronic engine controls. In the past few weeks I've noticed an odd phenomenon. After towing a skier at near wide open throttle, and going back to idle, the engine revs 2000+ rpm. Nothing I do with the engine/throttle seems to drop the speed. But if I turn off the engine and immediately restart it, the rpm returns to normal idle. I would have assumed that the throttle was sticking, but I cannot explain why stopping and restarting the engine immediately reduces the idle speed. Any thoughts?

[backfoot100]

Do you have a return spring on the throttle linkage at the carb that forces the throttle to close?
What happens if you throttle back but keep it in gear instead of going straight to neutral?

[rickturl]

I imagine I have a return spring, but have not checked recently!

When I remain in gear after throttle reduction the engine continues at an elevated rpm. I cannot go wakless - the engine is revving too high at the lowest throttle setting in gear.

Thank you.

[backfoot100]

You need to disconnect the cable to verify if its a carb or cable problem. I would disconnect the cable at the carb and manually operate the throttle at the carb itself.
Unfortunately, you'll have to remove the engine cover and have another person with you to steer and shift while you operate the throttle.

[rickturl]

Thanks for the suggestions. This may need to wait until spring - had to quickly winterize the boat due to approaching storms!

[RonT]

Worn cables, worn cable pivots behind the throttle, throttle return spring, cable adjustments off, can all cause this.

[rickturl]

Thank you Ron.  I'll look at rebuilding all this in the spring. Any thoughts on why turning the engine off and then back on - with no other action on my part - always cures the problem?
Rick

[shyskier]

Do you have speed control? perfect pass, ect.

[rickturl]

I do NOT have any electronic controls on this engine (eg: perfect pass.) It's all a simple mechanical system.
Rick

[Mason]

My boat has done the exact same thing recently.  I have cleaned and lubed all cables, linkages, springs, etc. under the hood and still have not eliminated the problem.  I replaced my carb about 3 years ago.  Is yours original rickturl?

My boat went into the shop for electronic ignition and some other upgrades a couple weeks ago.  I am going to see if anything I am doing including fresh oil in the motor and transmission will make a difference.  I have noticed that mine only idles high after running 85% to wide open throttle for more than about 3 minutes.  Also when I reduce speed to half throttle for a while prior to idling down sometimes it idles correctly and sometimes it idles high. 

Thanks for the original post.  I thought I was the only one experiencing this.   

[rickturl]

I have not resolved this issue as yet because the snow started falling! I was planning to take Ron's advice and service all of the throttle linkages in the spring - but it sounds as if you've already tried all that.  I did replace my carb about a year ago. It has been outfitted with an automobile carb and I swapped it for a marine carb. This problem began at least 50 hours into using the new carb, so I don't think swapping is the issue. However, it may need readjustment. Good luck resolving the issue - and please post any solutions so I can try them too!

[Mason]

I will keep you posted.  I went ahead and had mine winterized.  I was sick and the forecast showed mid 20's for the low so I went ahead and paid to have my boat winterized for the first time.  I hate to put it up for the year without knowing if my problems are cured or not.