Mercruiser 250 inline 6 idling problems

[Cbastuan]

Hey guys,
Working on my 1985 mercruiser inline 6 and I'm having a difficult time to get it to idle properly, I can get it to start and at higher rpms it runs fine, when I decrease the throttle it will idle down to roughly 900rpm, if I leave it there and let it run, after a few minutes it will slowly start to run worse and worse until it sputters and dies.
I rebuilt the carb last year following the instructions and video on mike's carburetor website.
I'm wondering if maybe it's an issue with the float? Is it slowing getting flooded? Cause if seems to be running rich.
Both of the idle mixture screws are turned out 1.25 turns.
So is the float a good place to start or should I be looking elsewhere? Just curious if I am missing anything.
Thanks for the replies.

 

[GA_Boater]

Did you adjust the idle screws for best idle in the water? 1-1 1/2 turns is just a starting point for the motor to run before making the final adjustment.

 

[Cbastuan]

No, I haven't had it on the water yet this year, I'd like it to just stay idling without stalling after a few minutes before taking it out on the water.
But I do plan to fine tune it once on the water.

 

[GA_Boater]

You can tune the idle screws on muffs enough to run in the water for the real fine tune.

 

[Cbastuan]

That's what I assumed but good to have it confirmed.
As far as the engine idling fine for a few minutes then getting progressively worse until it stalls do you think the float is a good place to start?
I know ita getting fuel cause when I pump the throttle the accelerator pump is squirting fuel into the carb and it starts fine, it just won't stay idling for more than a few minutes.
Do you think the float adjustment could be off and slowly flooding the carb or should I look elsewhere?
Thanks for the reply

 

[Bondo]

I know ita getting fuel cause when I pump the throttle the accelerator pump is squirting fuel into the carb and it starts fine, it just won't stay idling for more than a few minutes.
Do you think the float adjustment could be off and slowly flooding the carb or should I look elsewhere?

Ayuh,.... The color of the spark plugs oughta tell ya whether is floodin', or runnin' outa gas,...

 

[Cbastuan]

Ayuh,.... The color of the spark plugs oughta tell ya whether is floodin', or runnin' outa gas,...

Yes, I pulled a plug after it stalled, it was black and wet with fuel, the exhaust also smells of gas a little and is black/sooty.
The air/fuel mixture screws are set the standard 1 1/4 turns out.
Is it getting too much fuel or an incomplete burn somehow?
Just doesn't seem to make a lot of sense to me that it idles fine for a couple minutes then slowly gets worse until it stalls out.

I will be replacing the plugs this week just incase they could be the culprit but I don't suspect they are.

I will be updating the ignition to electronic and checking the timing as well.

Would the best course of action be to:

New plugs
Install electronic ignition
Set/check timing

Go from there?


Thanks

 

[Fishermark]

To your question on the float. Sure, it could be bad and causing the motor to flood out. They have been know to get pin holes and fill with fuel. You mention replacing the spark plugs. A good overall tune up / diagnosis is in order: compression check, vacuum gauge to see if it is steady, new points, condenser, etc.

Rebuilding a carb is pretty simple... but sometimes it just doesn't work.

 

[Cbastuan]

To your question on the float. Sure, it could be bad and causing the motor to flood out. They have been know to get pin holes and fill with fuel. You mention replacing the spark plugs. A good overall tune up / diagnosis is in order: compression check, vacuum gauge to see if it is steady, new points, condenser, etc.

Rebuilding a carb is pretty simple... but sometimes it just doesn't work.

Yeah, I did a fair bit of research before I rebuilt it, the float was brass and looked almost brand new I cleaned it, blew out all the passages/jets, and I did follow the video step by step, so I am fairly confident I did it properly, and the engine does seem to be getting plenty of fuel

 

[ziggy]

does the choke open all way as it gets warm?

 

[Cbastuan]

does the choke open all way as it gets warm?

It was definitely open, not sure if it was fully open though, should it be open all the way once it warms up and is idling?

 

[Fishermark]

should it be open all the way once it warms up and is idling?

Yes

 

[Cbastuan]

Yes

Ok, I put new new plugs in and adjusted the choke so there was just barely resistance on it when it was cold and so it would fully open once warmed up.
Also installed the pertonix ignitor kit.
Idles down nice and low now with no signs of bogging down or quitting.
Just need to adjust the timing to 6? btdc - I assume that will be to the left of the zero on the plate?
Sorry for the rookie questions kind of learnign as I go.
Thanks for All the replies so far.

 

[Fishermark]

Here ya go: