Mercruiser Carb Electric Choke adjustment

[blackrider]

Hello,
My name is Jared and I am from Cincinnati. I am new to boats but am a mechanic so I have the mechaical skills to work on my own stuff but am just unfamiliar with certain operations of boats mechanisms. After reading some of the posts on this board I am more than confident that someone can help me out. You guys all seem very good at what you do.

I have a Mercarb ( P/N 1389-9562 ) off of a 1989 Mercury Marine Engine (model MCM 3.0 litre ), displacement is 181, rated HP is 130HP. The thing was running terribly so I put new plugs, wires, points, condenser, rotor and rotor cap at it. I set the point gap at .022 on the peak of the rotor. After all of that it would at least idle without shutting down but it was iding very rough.

I just rebuilt the carb by following the manufacturers instructions. It is totally reassembled now and the linkages are back in place but I am a bit confused about the choke settings. Isn't the choke plate supposted to be wide open unless the electric choke engages it to close?

The way I set it up following the instructions has it mostly closed.

I can post pictures and video of the linkage in action if that will help.

Thanks in advance.

 

[CobiaXL]

Re: Mercruiser Carb Electric Choke adjustment

Choke should be closed when cold.Set the choke to close with very little resistance.Then 12volt will slowly open choke within 2-3 minutes usually.

 

[airshot]

Re: Mercruiser Carb Electric Choke adjustment

I rebuilt mine last year, the recomended settings for the choke were way off so gradually I kept resetting each time I cold started until I found the setting that worked best. Mine is set much leaner than what the instructions called for, however mine has been converted to electronic ignition as well. Do not know if that makes a difference or not, it is still a bit rich if the weather is warm, but starts well in the cold mornings in the fall.

Airshot

 

[blackrider]

Re: Mercruiser Carb Electric Choke adjustment

Ok, so with the carb off of the boat and set to facotry specs, the choke plate should be mostly closed even when in full throttle? And the electric chocke will make the remaining adjustments once it is hooked back up??

I used a 5/32" drill bit to check the measurement between the venturi wall and the choke plate edge when at wide open throttle.

Here is a picture in full throttle.

 

[blackrider]

Re: Mercruiser Carb Electric Choke adjustment

Choke should be closed when cold.Set the choke to close with very little resistance.Then 12volt will slowly open choke within 2-3 minutes usually.

So as long as I set the choke with the scribe mark in between the area that the manual says to, it will do the rest of the work for me?

 

[mpdive]

Re: Mercruiser Carb Electric Choke adjustment

Maybe....Your climate may dictate a different setting in your area compared to down south in the heat. After working on cars for over 20 years. I have found that with the engine cold, there should be a minimum amount of pressure holding the choke closed. In other words. if you turn the choke coil just until the choke valve closes, that is usually good enough. You only need an enriched mixture for a minute after startup before you want the electric coil to start opening the choke. Any tighter of an adjustment than that will result in too rich of a mixture for too long of an extended tiome. Additionally, a too tight setting will cause you problems whwn you stop the boat for five minutes or so and go to restart. If the choke has started to close down the mixture is too rich for an engine at operating temperature. Like I said, just barely enough pressure on the coil spring to close it and leave it. Oh and additionally, the setting your seeing in the photo is your WOT (wide open throttle) setting which is in place for a flooded engine. It allows the choke plate to remain at an angle to allow air into the engine. Again be aware of factory setting for chokes especially in warmer climates.

 

[blackrider]

Re: Mercruiser Carb Electric Choke adjustment

In other words. if you turn the choke coil just until the choke valve closes, that is usually good enough. You only need an enriched mixture for a minute after startup before you want the electric coil to start opening the choke. Any tighter of an adjustment than that will result in too rich of a mixture for too long of an extended tiome.

This answers my question. If I understand you correctly, it is normal for the choke plate to be closed off like this for a cold engine. ( Or in my case, it is sitting on my desk and the electric choke is not hooked up ) But under normal operating conditions, the choke plate will be closed if the engine is cold and the electric choke will open it up after a minute or two.
This is the mechanism I was not sure about but now that you explained it I feel a lot better in its operation. I have worked on ATV and motorcycle carbs before and they are manual chokes. I didn't understand how an old boat like this could have a "smart choke" if you will that knew when to open and close. LOL
I am located in Cincinnati and at times our temps can be very hot and humid like down South. We are not consistently hot and humid like in the south but we can get some of the same conditions.
I currently have the choke setup so that it took as little coil resistance as possible to close the choke plate.
Can you hook up the choke to a battery to test if it is working correctly? I know for a fact that when the engine was cold this choke plate was wide open.

 

[mpdive]

Re: Mercruiser Carb Electric Choke adjustment

This answers my question. If I understand you correctly, it is normal for the choke plate to be closed off like this for a cold engine. ( Or in my case, it is sitting on my desk and the electric choke is not hooked up ) But under normal operating conditions, the choke plate will be closed if the engine is cold and the electric choke will open it up after a minute or two.
This is the mechanism I was not sure about but now that you explained it I feel a lot better in its operation. I have worked on ATV and motorcycle carbs before and they are manual chokes. I didn't understand how an old boat like this could have a "smart choke" if you will that knew when to open and close. LOL
I am located in Cincinnati and at times our temps can be very hot and humid like down South. We are not consistently hot and humid like in the south but we can get some of the same conditions.
I currently have the choke setup so that it took as little coil resistance as possible to close the choke plate.
Can you hook up the choke to a battery to test if it is working correctly? I know for a fact that when the engine was cold this choke plate was wide open.

The choke spring is nothing but a thermostatic coil which under current loses tension. I would not waste my time with hooking it to the battery though. Older carbs used linkages and cams with electric assist and some use purely electric coils. If the engine is cold and it was linkage connected, when you pushed the throttle down, the tension on the cold coil spring closes the choke plate down. When it starts the choke plate has a slight opening and is running on a fast idle cam because it has to burn off the rich mixture. The coil is allready energized and starting to lose tension. After a minute or so when the throttle is opened, it kicks off the high idle cam into the main idle circuit. That's why having the bare minimum tension on the choke coil is so important because you dont want a rich mixture for a long time. I would just verify a closed choke on a cold engine, then fire it up and you will visually see the coil opening all on it's own. By the way, I was a Cleveland native till 4 years ago when we moved to SC. Go Bucks

 

[mpdive]

Re: Mercruiser Carb Electric Choke adjustment

Oh yea.....I wanted to add that if the choke is wide open and engine is running at operating temp, verify the setting on the idle mixture screws. It's vital for a smooth idle. If it still does not straighten out, I would be searching for a vacuum leak such as carb baseplate or vacuum line off or leaking. Let me know if I can be of any help.

 

[blackrider]

Re: Mercruiser Carb Electric Choke adjustment

Oh yea.....I wanted to add that if the choke is wide open and engine is running at operating temp, verify the setting on the idle mixture screws. It's vital for a smooth idle. If it still does not straighten out, I would be searching for a vacuum leak such as carb baseplate or vacuum line off or leaking. Let me know if I can be of any help.

A Cleveland native!!! I have family that lives in North Royalton. Go Browns?? LOL I lived in Columbia SC for about a year. Worked at the Columbia Airport as an aircraft mechanic. Hated that summer humidity! It was bad! Almost like Houston TX.

Ok, I will have to put this thing on the boat and see how it works. As for the choke plate being open, yes it was open when we didn't even have the engine running and before it was ever started. So I will have to verify that once installed on the boat.

But even after it was warmed up, the engine would not idle correctly. It would run fine as long as you kept the rpms just a bit higher than idle but would die with it in neutral. I have the idle mixture screw adjusted at 1 and 1/4 turns out as the book says and I will adjust as necessary from there.
This problem needs to be fixed because when trying to dock the boat or put it on the trailer, the engine will die if I go into neutral for even a second.

 

[mpdive]

Re: Mercruiser Carb Electric Choke adjustment

Sounds like your on the right track. Back out the screws even turns and look for an increase in rpm. Do it slowly and as soon as there is no change STOP. This can also be accomplished with a vacuum gauge connected to a vacuum port. Just watch for the highest vacuum reading. I personally start with the factory recommended setting and then screw the mixture screw in slowly until the engine starts to falter. Then I start backing it out just enough to receive the highest rpm. After all that check your idle speed and be sure its not way off. Too low and the engine wont stay running. If you get stuck, post it on here I will give you contact info.

If you have trouble keeping it running bump the idle speed screw by 50 rpms or so just to keep it running enough to adjust the mixture.

 

[blackrider]

Re: Mercruiser Carb Electric Choke adjustment

Where would I find the vacum hoses on this engine? I have seen a lot of people say to check these for leaks and now you are saying to hook up a gauge to it ( Which I have ) but I don't know where they are. I didn't see any Vaccum hoses going to the carb.

Any pictures or diagrams maybe?

How about a manual for this boat? I have seen people post them but the links were dead when I clicked on them.

1989 Wellcraft 17 ft boat.

 

[mpdive]

Re: Mercruiser Carb Electric Choke adjustment

Look under the carb baseplate for rubber hoses and see if any vacuum lines are there. If not I personally do it off of rpm. Just as accurate. Most important, make sure you idle speed screw is set somewhere close to factory specs or a bit faster to keep the boat running to roughly dial in the mixture. For example...If the boat calls for 650 rpm at idle you could bump to 750 just to do the initial mixture adj. Then when it straightens out turn the idle speed back down and readjust the mixture again and then tweek the idle speed to factory specs. I have a 2003 Stingray 3.0 that I had to set 30 rpms lower than factory to avoid dieseling. Just a bit of carbon buildup probably but it is just fine. Like I said if you get stuck send me your contact info and we will see if we can get you up and running.

 

[mpdive]

Re: Mercruiser Carb Electric Choke adjustment

I forgot to add.....Keep in mind that because of the lack of a fast idle cam on a marine carb, the operator has the responsibility of running the engine at a higher rpm upon startup until the engine warms up. On a cold start, a marine engine will not idle very well or not at all unless you are running it above idle.(900 rpms or whatever sounds good during the first minute)

 

[blackrider]

Re: Mercruiser Carb Electric Choke adjustment

I forgot to add.....Keep in mind that because of the lack of a fast idle cam on a marine carb, the operator has the responsibility of running the engine at a higher rpm upon startup until the engine warms up. On a cold start, a marine engine will not idle very well or not at all unless you are running it above idle.(900 rpms or whatever sounds good during the first minute)

MP THanks for all the help. I will get back to you when I get this thing installed back on the boat. Thanks for the offer for direct phone line tech support too!!

I'mm PM you if it comes to that. Thanks alot man.

 

[boltonranger]

Not sure this is correct. I have the 2 bbl mercarb and it does indeed have a fast idle cam. It does not, however, have a fully stepped cam that are on automotive carbs. It does the same job as a stepped one though I have found that closing the butterfly is too rich for my 3.7. Two marks rotation clockwise was the sweet spot for me. With one pump to the firewall and 1/3 throttle my engine acts like it ought to at a fast smooth idle until warm. This is maybe just under a minute and then the carb wants to kick the idle down. This is at roughly 70 degrees outside with a cold motor.

Re: Mercruiser Carb Electric Choke adjustment

I forgot to add.....Keep in mind that because of the lack of a fast idle cam on a marine carb, the operator has the responsibility of running the engine at a higher rpm upon startup until the engine warms up. On a cold start, a marine engine will not idle very well or not at all unless you are running it above idle.(900 rpms or whatever sounds good during the first minute)

 

[Bondo]

Ayuh,.... A 5 Year old thread,..??..??

Closed,....