3.0L Mercruiser does not always return to idle

[Gino27]

I have a 2001 Stingray with a Mercruiser 3.0 (non TKS) motor. I have had trouble with the carb in the past so I had my mechanic rebuild and tune it. The issues I had were hesitation in the throttle and trouble with starting. Now when I rev the engine or take it for a run, It only returns to a normal idle speed about 20% of the time (I think 650 rpm is spec). Most of the time the idle hangs around 1000 rpm and I have to snap accelerate in neutral to get it back down.

Any ideas what my problem could be?

 

[Bondo]

Ayuh,..... Welcome Aboard,...... You need to slightly lengthen the throttle cable at the carb,.....

The cable should hold a slight tension on the carb's linkage, against the idle adjustment screw,.......

 

[Gino27]

Ayuh,..... Welcome Aboard,...... You need to slightly lengthen the throttle cable at the carb,.....

The cable should hold a slight tension on the carb's linkage, against the idle adjustment screw,.......

I'll check on that. I thought I had given it plenty of tension but that was about a year ago.

But if that fix is to no avail, what should my next steps be?

 

[havoc_squad]

How you know if the cable preload adjustment still is not enough is if you run into the problem and can push the carb arm to its stop and the RPMs drop.

If it hasn't been done already by the service shop, the final carb idle mixture adjustment per service manual needs to be done in gear in the water at minimum idle.

www.boatinfo.no should have the OEM service manual for your motor and carb.

I am not near a PC now, so I can't say what manual number and page to reference.

 

[Gino27]

Mercruiser 3.0 idle issue

I have posted about this before but still cannot figure out my problem. As you can see in the attached video, when I bring the throttle back to idle, It gets hung up around 1000 rpm and eventually comes back down, or never comes down (like at the end of the video). If I pull on the throttle lever attached to the carb it will return so I tried to increase the return tension of the throttle cable but that did not help.

Any and all suggestions are welcome. Thank you!!

 

[Grub54891]

How did you increase the tension. There is no return spring on the motor. When returning to idle the cable should actually push the linkage to the idle adjustment screw. I think it needs a touch of adjustment.

 

[Bt Doctur]

If I pull on the throttle lever attached to the carb it will return so I tried to increase the return tension of the throttle cable but that did not help.

Remove the throttle cable adjust idle speed and there should be some type of retirn spring on the carb just incase the throttle cable should break.Check carb operation and return to idle. Install throttle cable with some downward pressure on the linkage forcing linkage against the throttle stop

 

[Gino27]

How did you increase the tension. There is no return spring on the motor. When returning to idle the cable should actually push the linkage to the idle adjustment screw. I think it needs a touch of adjustment.

I increased the pressure of the throttle cable against the linkage.

 

[Bondo]

I increased the pressure of the throttle cable against the linkage.

Ayuh,..... Then increase it abit more,....

 

[kenny nunez]

Be sure that the throttle lever is not loose on the butterfly shaft. The lever is “peeled” on the brass shaft but sometimes gets loose. See if you can wiggle it after advancing the throttle just off of the idle stop screw.

 

[Gino27]

Alright so I have the cable tension as much as I'm comfortable with. I also added a spring to aid in the return of the throttle. But I still have the same issue... if I rev the engine and throw it back to idle quickly, It comes back to idle. But, if I bring it back slowly (like I would to slow down on the lake) it hangs around 1000-1100 rpm. UGH!

 

[dezmond]

Maybe a silly question but is everything good and clean and lubricated? Might be gummed up and not running/moving smoothly? Just a thought.

 

[Gino27]

Maybe a silly question but is everything good and clean and lubricated? Might be gummed up and not running/moving smoothly? Just a thought.

Yeah everything is in check. I just had it rebuilt last summer. I've talked with a few mechanics from a couple of local marinas and they told me that my carb was part of a defective series that Mercury only made for one year and I would be best off replacing it with a newer model mercarb. Can anyone confirm this?

 

[oldsub86]

If it used to work, you should be able to make it work again. "Defective Carb" sounds like they had no idea or were just unwilling to tell you how to fix it.

 

[1999 Searay 180BR]

So, I dunno if you've resolved this problem or not but I'd like to chime in. First off, I'm not a licensed mechanic but my father and grandfather taught me at a young age how to work on things. I have done my own repairs most of my life and consider myself somewhat mechanically inclined. Back at the start of summer I removed my carb, totally disassembled it, soaked it in carb cleaner for two days, rebuilt it with a brand new rebuild kit, reinstalled it and immediately experienced the same thing you're describing. My problem was the throttle butterfly. There are two round plates that slide into the split shaft and are held in place by two small screws each. One would think that being round it wouldn't matter which plate went where or how they were oriented, but that wasn't the case on mine. If you remove the spark arrester from the carb and look down past the choke plate to the throttle plates they should close off COMPLETELY when the throttle control at the helm is in neutral. I had an ever so small gap and I suspect you may also. I also could give the linkage a little nudge or snap the throttle and it would idle down but otherwise it idled around 1000-1100 RPM. After removing the carb and disassembling the butterfly I mixed and matched and flipped/flopped the round plates in the shaft and it was immediately apparent when the correct combination was found. Put everything back together and now it purrs like a kitten at 650 RPM... Hope this Helps

 

[Gino27]

So, I dunno if you've resolved this problem or not but I'd like to chime in. First off, I'm not a licensed mechanic but my father and grandfather taught me at a young age how to work on things. I have done my own repairs most of my life and consider myself somewhat mechanically inclined. Back at the start of summer I removed my carb, totally disassembled it, soaked it in carb cleaner for two days, rebuilt it with a brand new rebuild kit, reinstalled it and immediately experienced the same thing you're describing. My problem was the throttle butterfly. There are two round plates that slide into the split shaft and are held in place by two small screws each. One would think that being round it wouldn't matter which plate went where or how they were oriented, but that wasn't the case on mine. If you remove the spark arrester from the carb and look down past the choke plate to the throttle plates they should close off COMPLETELY when the throttle control at the helm is in neutral. I had an ever so small gap and I suspect you may also. I also could give the linkage a little nudge or snap the throttle and it would idle down but otherwise it idled around 1000-1100 RPM. After removing the carb and disassembling the butterfly I mixed and matched and flipped/flopped the round plates in the shaft and it was immediately apparent when the correct combination was found. Put everything back together and now it purrs like a kitten at 650 RPM... Hope this Helps

I know you replied to this ages ago, but I was getting around the unwinterizing my boat and I noticed I have exactly the issue you were describing. I’ll try to fix it without completely tearing the carb apart.

 

[Gino27]

So I went to remove the butterfly valves, forgot they were mushroomed at the top and broke a screw. I guess I'll have to drill out and tap? I'm kinda up a creek now

 

[Dremmick1985]

Did you ever figure out the issue?