mercruiser 4.3 v6 carb, choke wont idle

J

j1mmy420

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Joined
Apr 21, 2008
RO Number
29920
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6
Hello to all.
I have a 1997 Bayliner Capri with a 4.3 l mercruier lx
My problem is It will not Idle. I just replaced the Gas, Feul Pump, Water Seprator, and Starter I also ran some Seafoam in the Gas to clean things up a bit. Its been about 2 years since the last car rebuild. Here are the syntoms;
above idle (2500 - wot) runs great. But anything less the idle jumps up and doen until it dies. I only have 1 adjustment screw on the front of the Carb. It is turned all the way in with 1 and half turns out.
I tinkered around with the card and If I hold the Butterfly to almost closed it will idle pretty darn good. It will also rev really nice and then drop back to around 1000 rpms witout stalling. Could this just need a choke adjustment??
or is my engine starving for gas?? I appreciate any help you can give me.
I cannot put the boat in neutral without stalling and I have to slam it into gear if i want to keep the motor running..
 
Ayuh,.....

The Idle circuit is Plugged.....

Rebuild,+ then Readjust the Carb....
 
DO NOT SHIFT THE ALPHA's AT 1000 RPM or higher. You'll break the gears or dog clutch.

There's an idle adjustment screw on the port side of the carb.

Is the engine warmed up when the engine won't idle?
 
engine wont idle when warm or when cold. I am going to attempt a rebuild
DOes anyone have any tips or schematics etc...
 
Well...
I pulled the carb and did a rebuild. Actually was easier than I thought is would be. I bought a carb rebuild kit that came with all the gaskets etc. bought the paintcan of carbclean with basket also bought 2 cans of berrymans carb cleaner. printed out the specs and step by step instuction pdf file i found on another site.
After I put everything back together the bost fired right up with a nice and steady idle until.............
once the boat warmed up the engine stalled and continued to do the same thing as before. would only idle if i hold the choke partually closed.
any advise
was a sad day
 
You have a fuel restriction or fuel line leak. Check vent line, anti-siphon valve and fuel line connection and fuel pump pressure.
 
quote:
Originally posted by jtybt15

You have a fuel restriction or fuel line leak. Check vent line, anti-siphon valve and fuel line connection and fuel pump pressure.

Click to expand...
If all that Charlie mentions fails, you might have to take it back apart and clean it again. Use compressed air in every passage. Sounds like it might still be the idle circuit restricted.
 
Gee, I thought he rebuilt it....and it was easy.[:I]
 
If that "1 adjustment screw on the front of the Carb" is an idle mixture screw and not just idle speed screw, the 1 1/2 turns out spec is likely just a base setting to get the motor running and should be fine-tuned for strongest manifold vacuum with a vac gauge. It may just need to be turned out slightly for enrichening.

Even adjusting for highest idle rpm and smoothness by tach and ear for good compromise position, but very slightly out on the rich side may help. If it does help, back the idle speed screw off and repeat the fine-tuning with the mixture screw.

Never screw the mixture screw all the way in hard. If that was possibly done in the past it might be worth taking the mixture screw out and carefully inspecting the needle seal for grooving. Was that checked when servicing the carb?
 
I inspected the mixture screw and spring everything looks good. I actually blew compresses air in every hole, and everywhere I can see. I set the idle screw 2 turns in after touching plate. I set the mixture screw 1 and half turns out. I have not attempted to fine tune it. I have a brand new fuel pump installed. Like I stated before It fires right up and idles fine untill the choke opens and then stalls and dies. Although How long should it take for the choke to fully open. the choke is set at the middle setting. seems like the choke opened in about a minute that seems to quick.
 
Will it idle after the engine fully warms up? If not, you have a lean condition caused by fuel restriction.
 
Is it a Rochester carb on that 4.3? Mine calls for an initial setting of 4.5 turns out on the mixture screws. Cold or warm it is starving for fuel since playing with the choke keeps it running. Start with the mixture and if that fails the supply problem is elsewhere.
 
I had the exact same problem. Mine is a 1999 4.3 with Thunderbolt V ignition. The previous owner had the carb rebuilt and had intermittent problems thereafter. I bought the boat after is sat for a year. I ran the boat once for 3 hours and ran perfect. Three weeke later, I took her out again and couldn't operate below 1000 RPM. Docking is fun! I removed the carb, bought a rebuild kit. Went to install it and none of the jets would budge. There was a good bit of corrosion in the bowl and every steel piece was rusted. I took it to my dealer and he recommeded a new carb. Not cheap, $650. I picked it up yesterday but it is slightly different. The gas inlet is in the front vice side and there is a big vaccuum tube on the back of the carb. No such animal on the old one. What did the inside of your carb look like? Were you able to remove the jets and thoroughly remove any corrosion? or did you just spray and blow everything out and put in new gaskets? My manual calls for 1.25 turns as an initial setup and then adjust while in gear and in the water to fine tune.
 
I reread your posts and have a couple more thoughts... How do you have your choke set? My book says to align the little guiide two to two and a half marks "rich" or clockwise. That's how mine is set and it worked well once, not so much the second trip. I think you still have some dirt or corrosion floating around in the idle circuitry. This E-10 is wonderful stuff for cleaning things. Have you dumped you water separator into a clear jar and looked at the contents? You may have some phase separation going on and that's plugging things up too.
 
The low speed air screw needs to be adjusted. The 1 1/2 turn is a base setting and may not even be the correct setting for your engine/carb combination(as Don indicated) A settibg too closed will not let the engine idle at all. A setting too far out will make the engine run rough and may die. You can get a close setting simple by turning the screw both in and out to find the smoothest/highest idle setting. When the idle starts working, reset the idle screw(on the side) to the recommended RPM(usually somewhere between 650-750)

The low speed air screw only affects the fuel/air mixture at LOW SPEED.

There are usually TWO low speed air screws...unless you have a ONE barrel.
 
I appreciate everyone's feedback
I have a new water seperator,
WHen I took the carb apart the bowl was full of white crap. Everything else on the carb is brand new looking no rust or scrathes aside from the white residue. I cleaned it best i could and blew air in all the holes. I set my choke to match up the middle notch to the marking on the choke if that makes sense. I took her on the water and tried to adjust the air fuel mixture screw but did not get much better although it did improve a bit.
When we fist launched the boat It idles smooth and we went off in the no wake zone. Almost to the end the bot started and I had to up the Rpms a bit to keep it running. I have to say It runs alot smoother and better throttle response.

I am going to open the carb up again and see if their is more white crap in the bowl again
does anyone have a picture or diagram of the " idle circuit"
where exactly on the carb would that be located so I can place extra attention to that area
 
Basically,the idle circuit is a passage from the float bowl to the carb primary throat(s). the passage is a small diameter opening even with the primary throttle plate. As air rushes past the opening between the throat body and throttle plate, it creates a vacuum that pull fuel out the opening. As soon as the throttle opens a little further the throttle plate is no longer in close proximity to the idle circuit opening and the air no longer rushes past and looses the vacuum effect.

By any chance do you have fiberglass fuel tanks? I've never seen white stuff in the carb.
 
"The gas inlet is in the front vice side and there is a big vaccuum tube on the back of the carb. No such animal on the old one."

That's probably cause you got yourself a carb for an Automotive Application. Carbs for Cars and Boats are NOT the same.
 
I do have a fiberglass tank.
I guess I will rebuild one more time and see what happens. Going to have to wait till next week. I have to order a new carb kit from NAPA
 
Ethenol is disolving some fiberglass tanks and going into the fuel supply. I heard of black residue but not white. Ask around.
 
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