High idle, keeps running after shutting off

Ramanonos

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I was recently on this forum regarding bad fuel & mechanical fuel pump issues. All is well there, but now when i start her up, she idles at 2100 rpm. She starts up fine and purrs ehen I take it up to 3500rpm. But when I shut her off, it keeps running for about 5secs - but it mostly is a burp/fart kind of running. Not sure what that is. Should I screw with the idle on the carb? If so how&where do I do that. I should add that in my previous quest to find the fuel problem I took off the carb (2barrel) to take a look for any fuel I could dump out by tipping it over. I put the carb back on no problem. Also, i replaced the fuel pump (original issue). Given those two things is there anything I should be doing/checking? The high idle and burp/fart thing after shut off seems to be an issue (hopefully not a big one). Thanks again.
 

Ramanonos

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Re: High idle, keeps running after shutting off

Oh, and I have a new refirb 357 5.7L Mercruiser with a 2bbl carb
 

Don S

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Re: High idle, keeps running after shutting off

she idles at 2100 rpm

That's not idle rpm, 650 to 700 is idle rpm. You are at mid rpm at 2100 :eek: Hate to think how the drive is dealing with that rpm.

Remove the shift cable from the carb and get it slowed down. Then adjust the cable to fit the carb.
 

Ramanonos

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Re: High idle, keeps running after shutting off

Thanks. Sorry, I'm new to this. How do I remove the shift cable, and adjust cable exactly?
 

Don S

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Re: High idle, keeps running after shutting off

I have no idea, have nothing on a 357. Post a picture of the carb, the linkage and where the cable hooks up.
 

Ramanonos

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Re: High idle, keeps running after shutting off

Some pics
763e454a.jpg

fc1daa58.jpg
 

Ramanonos

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Re: High idle, keeps running after shutting off

Found the culprit! It's the thottle cable bar that's connected to the carb. I noticed it buckles up a bit when i rev it up and stays that way when i go back to idle. I went over to the engine while in idle nd pushed down on the bar with my hand. Went right down to 700rpm, which i think is where i want to be. So... Glad i found the problem, but I'm not sure what to do about it???
322d5662.jpg
 

Don S

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Re: High idle, keeps running after shutting off

Perfect, now, in my picture.
1. Warm the engine so choke is open.
2. Remove nuts A and B. Remove throttle cable from both (don't loose any parts)
3. Adjust the idle speed adjustment screw counter clock wise to slow the idle speed to 650 rpm. (make sure choke is wide open and engine warm)
4. Adjust cable adjuster so cable puts a slight pressure on the carb linkage at B location toward the idle position.



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Ramanonos

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Re: High idle, keeps running after shutting off

OK. I messed around with the idle screw first. One revolution counterclock. Got it down to 1100, but things sounded rough, like my engine was going to stall out. I may have made things worse.
 

Don S

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Re: High idle, keeps running after shutting off

OK. I messed around with the idle screw first. One revolution counterclock. Got it down to 1100, but things sounded rough, like my engine was going to stall out. I may have made things worse.

No, you probably need to adjust the idle mixture and probably the timing to match the lower rpm, and work back and forth until it all works together at the same time.
 

Ramanonos

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Re: High idle, keeps running after shutting off

Thanks Don. Your input is excellent. Im kinda of embarrassed to say that I dont know how to adjust the idle mixture or timing. It would be great if you could point me in the right direction?
 

Ramanonos

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Re: High idle, keeps running after shutting off

Now im in big trouble!!! I took off both A and B as you suggested. Went to fire her up and i heard a pop (from the carb), and it maxed out rpms. I put the throttle rod back on and now it wont start. Help
 

Don S

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Re: High idle, keeps running after shutting off

You have Thunderbolt V ignition, it needs to be put into base timing mode to set timing and idle rpm. Mixture adjustment and doing it all at the same time is probably just a bit more than you can handle, or someone can explain on a forum.

Not trying to be mean or anything like that, but your best bet is to take it to a Merc dealer and get it set up correctly the first time. Then learn to keep up with the it as you go.
 

Ramanonos

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Re: High idle, keeps running after shutting off

OK. Got it started with a full clockw rev of the idle screw. Unfortunately all the mechanics are 2 weeks busy list given the summer season. I'll have to make do on the DIY route. Thanks anyways
 
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