3.0LX Carb Issues (mixture screw?)

[brsox88]

So I have a 1996 3.0LX with DEI that will start when I give the carb a little throttle, if you bring the throttle lever back to the idle position the engine will die.

What I am thinking is happening is the carb is getting too much gas at the idle position which is why it dies which would make it running rich. Is there a mixture screw I should try playing with. Are there factory specs on what the screws should be set to? Just trying to figure out what a merc mechanic would do...

Ohh yea, tested the fuel pressure...6lb.

 

[Don S]

Re: 3.0LX Carb Issues (mixture screw?)

Do you let it warm up before you put it to idle? It's not EFI like your car.

 

[45Auto]

Re: 3.0LX Carb Issues (mixture screw?)

Has it ever idled before?

Did you "adjust" anything on the carb or change anything else to make it quit idling?

 

[bds85466]

Re: 3.0LX Carb Issues (mixture screw?)

As Don implies, assuming you are letting it warm up/un-choke properly, you could be onto something with idle mixture, but it'd be tough to say without more information.

Is your idle speed screw set to spec? Is your carb clean?

 

[brsox88]

Re: 3.0LX Carb Issues (mixture screw?)

I do let it get up to running temp (150). I took the carb apart yesterday and spent over an hour going through with compressed air and carb cleaner cleaning it out. Did make starting possible again but it wont idle, it just dies out nearly instantly. It also has high hesitation when you try to give it more throttle.

I haven't touched any of the adjustments. I just wanted to know if anyone had the "Factory Specs" so I would know if everything is set correctly. I bought the boat knowing it had idle issues.

 

[Don S]

Re: 3.0LX Carb Issues (mixture screw?)

Sounds like the idle circuit in the carb is still plugged up. Did you let it soak in carb cleaner (Not just the spray stuff) then blow all the passages out? Did you VERIFY all the passages were open after you cleaned it?
Not all carbs are rebuildable.

 

[brsox88]

Re: 3.0LX Carb Issues (mixture screw?)

Sounds like the idle circuit in the carb is still plugged up. Did you let it soak in carb cleaner (Not just the spray stuff) then blow all the passages out? Did you VERIFY all the passages were open after you cleaned it?
Not all carbs are rebuildable.

I took out every jet, screw, passage and cleaned them all and sprayed them as well. Only screw I couldn't get is the one that sits on the inside of the carb at the bottom of the bowl. Has like a pin with a spring in the middle. I still sprayed and blew air through it though.

There is what, only two screws on this carb right. Anyone know the turn specs on them, maybe I can then verify those are right atleast? I can imagine this is a common carb too as these 3.0l are are dime a dozen it seems.

 

[Don S]

Re: 3.0LX Carb Issues (mixture screw?)

Check for a vacuum leak. Start the engine and run it at what ever speed it will run, then spray some break clean, carb cleaner or WD40 around the base of the carb and the intake manifold where it bolts onto the head. If it changes the way the engine is running, you found a leak.
No vacuum, no idle.

 

[brsox88]

Re: 3.0LX Carb Issues (mixture screw?)

Check for a vacuum leak. Start the engine and run it at what ever speed it will run, then spray some break clean, carb cleaner or WD40 around the base of the carb and the intake manifold where it bolts onto the head. If it changes the way the engine is running, you found a leak.
No vacuum, no idle.

Ok, so I did what you said Don. Video of it is below. I didnt notice any spike in the engine. I did get it to about 700 RPM with the engine shaking a lot then finally smoothing out for about 5 seconds then always dieing. It always loves to backfire when trying to start, and has trouble starting even with the throttle (currently still only way to start it). After it stalled I pulled the flame arrestor and noticed a pool of gas down in the throttle body neck above the flaps with the boat off and key off. (sorry for the bad terminology)

http://www.youtube.com/watch?v=iro7Ognq5l0

 

[brsox88]

Re: 3.0LX Carb Issues (mixture screw?)

Any ideas? Anyone? haha

 

[bds85466]

Re: 3.0LX Carb Issues (mixture screw?)

It also has high hesitation when you try to give it more throttle.

This isn't your whole problem by any means, but this snippit may imply that the accelerator pump isn't performing correctly. Or your throttle is loopy.

Pooling gas is probably another hint...but I'm not positive on the root cause. How is the float looking? Don't know what the specs are, but level and drop may be worth looking at -- or if it's cracked or something.

Has this engine ever idled or is this something that's recently just come on?

 

[Don S]

Re: 3.0LX Carb Issues (mixture screw?)

Sounds like a bad miss to me. Have you checked for spark on all cylinders? Do a compression test to. Look at the spark plugs, do they look like they are firing equally? Does the choke open when warm?