5.7 runs but won't idle after winter storage

[nextboat1]

Hello, I have carbureted mercruiser 350 that runs well at around 1500 rpm but will not idle even after warm up. It has fresh fuel and a fresh fuel filter. It has good throttle response but will not run below 1500 rpm for more than a few seconds. Any idea as to what could be causing this? Carb? Ignition (points)? Any help would be greatly appreciated. Thanks.

 

[Don S]

Re: 5.7 runs but won't idle after winter storage

What is your engines serial number. Not all 5.7 carbed engines are the same, and year doesn't mean much either.

 

[nextboat1]

Re: 5.7 runs but won't idle after winter storage

I'm not currently by the boat, but I can get the serial number tomorrow. I can tell you that the Carb is a quadrajet if that helps.

 

[Bondo]

Re: 5.7 runs but won't idle after winter storage

I'm not currently by the boat, but I can get the serial number tomorrow. I can tell you that the Carb is a quadrajet if that helps.

Ayuh,.... Welcome Aboard,... Sounds like it's idle circuit is Plugged....

Probably oughta throw a cleanin', 'n kit into it....

 

[Don S]

Re: 5.7 runs but won't idle after winter storage

Well, if it has a Qjet, it doesn't have an electric fuel pump so that's not the problem.
Does the engine die when you let the key off from the start position, or does it run on it's own for a few seconds.
Does it start right back up after it dies or do you have to wait for some amount of time?

 

[nextboat1]

Re: 5.7 runs but won't idle after winter storage

It will run for a few seconds and then die with the throttle at idle position. It will immediately fire back up with the same result. The only way I can get it to stay running is to throttle it as soon as it starts and bring the rpm up to around 1500 or so. Above 1500 it runs fine, anything below and it will run briefly then die out. I have also ran the engine up to temp to try to rule out a choke issue. Thanks Don. I hope this info helps.

 

[frantically relaxing]

Re: 5.7 runs but won't idle after winter storage

Don't rule out a choke issue unless you actually SEE that the choke is open. Me, I set my chokes so they never fully close.

That said, I concur on the idle circuit issue. The starboard Rochester in the SkipperLiner had an idle issue from the day we bought it. About 4 years later (3 years ago) it started doing exactly what yours is doing. I pulled the carb, grabbed some carb cleaner and some pins and sewing needles and I got all kinds of hardened crud out of the thing. Carb cleaner did most the work, and she's run perfect ever since. And upon returning to the dock on our maiden voyage a couple of weeks ago, the port engine died while parking. Just like the starboard used to do, so THAT carb will be coming off (if it ever quits snowing!)

 

[nextboat1]

Re: 5.7 runs but won't idle after winter storage

Update:
Today I had a chance to try a few things on the boat. From the replys that I have gotten, I suspect that the Carb is "gummed" so to speak. I first ran the idle mixture screws all the way in, counting the turns as I went. I then brought them back out to there original position. (2.5 turns). Tried starting, no luck. Second, I removed the flame aresstor and sprayed a little Carb cleaner down into the Carb. With the throttle lever set in the idle position, I hit the key and she fired right up, ran at 850 rpm, and then died after it burned up all of the Carb clean. Would I be right in assuming that this would iindicate that the engine is running lean and in need of more fuel? Is a rebuild in order or is it possible to try something else before that has to happen? Thanks for all of the help thus far.

 

[Don S]

Re: 5.7 runs but won't idle after winter storage

The only way to clean a carb is to remove it, take it apart, soak in carb cleaner until clean, blow all passages out with compressed air, verify passages are all open, reassemble with a carb kit and set to specs. Install on engine, run and readjust to idle mixture to suit engine.

Spraying on the outside of the carb or down the throat does nothing.

 

[NHGuy]

Re: 5.7 runs but won't idle after winter storage

That sounds like the idle circuit is plugged up.
If you are into detail and want to repair it yourself get Cliff Ruggles book How to Rebuild and Modify Rochester Carburetors. Once it's opened up you might as well do the job right.
If you want it fixed quick and right find the crankiest old carb guy around, expect to spend $250 to $350. Those guys have forgotten more than I will ever know!

 

[Eric 3.7LX Alpha 1]

Re: 5.7 runs but won't idle after winter storage

Here are several videos of the process (breaking down, cleaning, and assembly), to go along with your service manual, made by Alpheus:

http://forums.iboats.com/mercruiser...er-quadrajet-rebuild-video-update-362542.html

 

[frantically relaxing]

Re: 5.7 runs but won't idle after winter storage

Actually, with a little luck, some very small wire or drill bits and some carb cleaner, it MAY be possible to fix your idle problem without removing the carb.

Check the pic of my spare Holley below. The arrows are pointing to air bleed holes. These are behind the secondary barrels, and these particular air bleeds draw air into the secondary fuel circuit to help atomize fuel. Since my carb's choke plate is shut (and not shown anyway), you can't see the idle bleed holes which are in front and above the primary barrels, but they're pretty much exactly the same. Your Qjet won't look like this, but it should have similar air bleed holes. Since you stated that turning out your idle air screws does nothing, chances are your idle air bleeds are plugged, because that's where the air comes from that you're trying to adjust. You'll need some very thin craft wire, or a straight pin, or a drill bit that's smaller than the hole-- good luck, and because drill bits that small break easily, I prefer wire or pins... first, take the hose on your can of carb cleaner and force it against the bleed holes, then spray. Cover your face because it WILL spray right back at you! Then "ream" the hole gently with the wire or pin. Spray and ream a few times. If you're lucky, your bleeds may just be gummed up with a little varnish and cleaning them out may do the trick. If it works, great! If not, you're only out a few minutes of your time and a buck's worth of carb cleaner...

 

[nextboat1]

Re: 5.7 runs but won't idle after winter storage

Thanks, ill definitely give that a try, if the weather ever cooperates.

 

[nextboat1]

Re: 5.7 runs but won't idle after winter storage

Thanks for all the help guys! I ended up cleaning the Carb and throwing a rebuild kit in it, and now it idles great. I did run into another problem that I will be posting in a new thread. Thanks again!