Hard starts after sitting for a week or so

[poconojoe]

2003 Mercruiser 4.3L, 2 bbl carb.
Engine serial # OM643729

Engine hard to start after the boat has been sitting for days.

After it starts, it runs fantastic and will restart just fine with minimal cranking even after anchored out for hours.

Ignition wires, plugs, distributor cap, ignition sensor replaced a few years ago.

I checked under the distributor cap and it looked good. Very little tarnishing. I did clean it anyway.

New starting battery.

I suspect the choke.
After sitting in my driveway for 3 days, I looked at the choke and it was not fully closed.
I turned the key to the "on" position and moved the throttle fully open and back a few times. There was definitely gas in the carb, but the choke was still not fully closed. It had about 1/4" or more open gap between the butterfly and carb throat.

I tried loosening the three screws and rotated the choke adjustment, but the butterfly stayed in the same position.

There are two wires connected to choke adjustment. One (+) connected to the center and the other (-) connected to one of the three screws holding the adjustment tight. Is that the proper location for the (-) wire? Seems like not the best place to get a ground if you ask me.

So, I guess what I'm asking is the proper procedure for adjusting the choke when cold and if the butterfly should be fully closed when cold.

Also, when should there be power to the choke adjustment wires? Are they energized when it's cold or when it's hot? How does the ignition system know when to energize these wires?

Sorry for the winded post, but I wanted to make sure I give as much info as possible.

Thanks as always.
Joe

 

[Scott06]

If choke is only closed till there is a 1/4” you have to loosen up the element and linkage so it does close fully . You should be able to twist it with some effort
U pump the throttle to set the choke ( close it ) and power is applied when the engine runs eventually heating up the choke coil until it opens. Choke will stay open by the linkage until u pump the throttle to set the choke on restart

Would check with a spark gap tester you spark is good and hot what do the plugs look like

 

[poconojoe]

If choke is only closed till there is a 1/4” you have to loosen up the element and linkage so it does close fully . You should be able to twist it with some effort
U pump the throttle to set the choke ( close it ) and power is applied when the engine runs eventually heating up the choke coil until it opens. Choke will stay open by the linkage until u pump the throttle to set the choke on restart

Would check with a spark gap tester you spark is good and hot what do the plugs look like

Thanks for the quick reply.

Ok, so the choke plate should indeed be fully closed when cold starting. I suspect this is the problem.
If I mess with the linkage, it will close.
But, just pumping the throttle doesn't do it.
There is an an adjustment set screw on a cam on the linkage, but I don't see how that would change the position of the choke plate.

From my ancient memory, I seem to recall that loosening the three screws and twisting the choke adjustment a bit would open or close the choke plate. But I could be remembering things wrong.

I'm going to go out and mess with it some more.

Engine runs great, it's just the initial startup, but maybe I should check the plugs and spark as you suggested.

 

[poconojoe]

Ok, I messed with the choke adjustment disc some more and got it close all the way. I loosened the three screws and rotated it counterclockwise and pumped the throttle. I did this in small increments until I got the choke plate to fully close.

I guess my old memory was correct about how to adjust it and your confirmation of the fact that it should be fully closed helped a lot. Your explanation on how the choke is disengaged also helped.

I'll see how it acts when we go out this week, but I'm confident this was causing the hard cold start problem.

Thanks again for your help.

 

[Scott06]

Thanks for the quick reply.

Ok, so the choke plate should indeed be fully closed when cold starting. I suspect this is the problem.
If I mess with the linkage, it will close.
But, just pumping the throttle doesn't do it.
There is an an adjustment set screw on a cam on the linkage, but I don't see how that would change the position of the choke plate.

From my ancient memory, I seem to recall that loosening the three screws and twisting the choke adjustment a bit would open or close the choke plate. But I could be remembering things wrong.

I'm going to go out and mess with it some more.

Engine runs great, it's just the initial startup, but maybe I should check the plugs and spark as you suggested.

Sorry you have to adjust the linkage such that when u pump the throttle it closes all the way maybe 1/16” gap

When it warms the coil will open the choke flap completely vertical .

The linkages can get corroded and gummed up the heating coil doesn’t consistently work etc

 

[poconojoe]

Sorry you have to adjust the linkage such that when u pump the throttle it closes all the way maybe 1/16” gap

When it warms the coil will open the choke flap completely vertical .

The linkages can get corroded and gummed up the heating coil doesn’t consistently work etc

I have it set now at no gap. It's fully closing.
Should I have it open a crack, like 1/16"?

I'll spray the linkage.

 

[poconojoe]

Ok, after adjusting the choke it fired right up.

 

[Silvertip]

Hope you made choke adjustments with engine stone cold!

 

[poconojoe]

Hope you made choke adjustments with engine stone cold!

Absolutely! It was sitting in the driveway for a week.

Should the choke butterfly be completely closed when cold or should I have left a slight gap?

 

[nola mike]

I thinklutely! It was sitting in the driveway for a week.

Should the choke butterfly be completely closed when cold or should I have left a slight gap?

I think spec is ⅛"or so. But whatever works best for you. Mine doesn't need much if any choke in the 90' weather that I'm usually in, so I dial in a bit more so that it will open fully earlier

 

[poconojoe]

I thinklutely! It was sitting in the driveway for a week.

I think spec is ⅛"or so. But whatever works best for you. Mine doesn't need much if any choke in the 90' weather that I'm usually in, so I dial in a bit more so that it will open fully earlier

Yeah, I'm thinking the way it was initially running that I should re-adjust it so there's a slight gap.

 

[Scott06]

Absolutely! It was sitting in the driveway for a week.

Should the choke butterfly be completely closed when cold or should I have left a slight gap?

Spec is a tad over 1/16” so slight gap if it’s working you must have done something right…

 

[Silvertip]

A 1/16 inch drill bit works as a gauge.

 

[poconojoe]

Great! Thanks for the replies!

 

[flashback]

late to the party, but make sure that it opens completely when warmed up.

 

[poconojoe]

late to the party, but make sure that it opens completely when warmed up.

I did exactly that. It was indeed fully open, but good point!

 

[Lou C]

Also as far as hard starting remember that the linkages must be clean and there is usually a vacuum operated or linkage operated choke pull off. This pulls the choke plate open just a fraction of an inch to give the carb enough air to keep running.
The choke basically increases the effect of Bernoullis law to pull more fuel thru the idle system for a richer fuel mix. This compensates for the tendency for fuel to condense out of the mixture on the cold walls of the intake manifold. Once everything heats up the rich mix is no longer needed and the choke should be fully open. I actually prefer the old manifold heated chokes because they follow engine temp. Electric chokes do not they are on a timer heater system & in some cases they open too fast. But that’s what you see no with both Holley & Edelbrock marine carbs.

 

[poconojoe]

Also as far as hard starting remember that the linkages must be clean and there is usually a vacuum operated or linkage operated choke pull off. This pulls the choke plate open just a fraction of an inch to give the carb enough air to keep running.
The choke basically increases the effect of Bernoullis law to pull more fuel thru the idle system for a richer fuel mix. This compensates for the tendency for fuel to condense out of the mixture on the cold walls of the intake manifold. Once everything heats up the rich mix is no longer needed and the choke should be fully open. I actually prefer the old manifold heated chokes because they follow engine temp. Electric chokes do not they are on a timer heater system & in some cases they open too fast. But that’s what you see no with both Holley & Edelbrock marine carbs.

Great info!
Thanks!