Quadrajet carburetor choke

When my engine, a Mercruiser 228 is warmed up I notice that the choke lever has only moved about a quarter of an inch and that the engine tends to cut out when I am moving through neutral from forward to astern or vice versa. Increasing the tick-over cures the problem but of course means the engine is running at higher revs. When I switch off, the choke lever immediately fully opens. If I start up again the choke lever returns to being about a quarter inch open. Does all that indicate a choke problem? Thanks for any help received.

can you post a overhead view of the carb ? yes you do have a problem.

The QJ carb choke plate is controlled by a spring, be it external on the intake or inside the choke housing. The spring, when cold, forces the choke plate to the closed position and at the same time engages the fast idle speed cam. When the motor starts, vacuum applied to the choke pull off opens the choke plate slightly to allow for a richer mixture cold. As the spring heats, it relaxes the tension and allows the choke plate to fully open and drops the fast idle speed cam allowing normal base idle speed. If the choke plate stays closed, or only partially open either the choke spring is failed, or, the choke pulloff was installed incorrectly. If the motor shuts off and the plate opens fully (if I read this correctly) I would suspect the choke pull off linkage.

Thanks for your reply. I'll try and do what you request.

Thanks your help, I'll check spring, etc. and let you know outcome

larrys toy said:

The QJ carb choke plate is controlled by a spring, be it external on the intake or inside the choke housing. The spring, when cold, forces the choke plate to the closed position and at the same time engages the fast idle speed cam. When the motor starts, vacuum applied to the choke pull off opens the choke plate slightly to allow for a richer mixture cold. As the spring heats, it relaxes the tension and allows the choke plate to fully open and drops the fast idle speed cam allowing normal base idle speed. If the choke plate stays closed, or only partially open either the choke spring is failed, or, the choke pulloff was installed incorrectly. If the motor shuts off and the plate opens fully (if I read this correctly) I would suspect the choke pull off linkage.

Click to expand...

Just one correction here.........

Marine carburators do NOT have a fast idle cam. The cam that the throttle (idle) screw sits on it all the same profile. Just round. NO steps!!

Also The choke butterfly may not open 100% at idle.

When adjusting the choke butterfly on a (mechanical) choke.
Manual choke in my opinion is one with the bymetal spring on the manifold.
The other style is a black (electric) module with two wires going to it That heats up a bymetal spring inside the module.

WHich do you have?

If it is the mechanical type, you have to adjust it when COLD.

The way it works is,

Disconnect the throttle cable from the carb. activate the throttle lever about 1/2 its travel one time. The choke butterfly should slap shut.

At this point you would bend the choke rod that goes to the by metal spring to make the butterfly open.

This is a bit tricky to a novice......As long as the butterfly shuts any additional movement of the spring/rod is not needed so the rod can be tweaked.

The rod is typically shaped like a stretched out sideways Z
See image if you can.

Granted, I have rebuilt hundreds of QJ carbs in my life working on automobiles, but the basics of the choke circuit should remain the same between the two. Having never rebuilt a "marine" QJ, there may be no fast idle cam.
However, I am confused by the statement, when cold: "At this point you would bend the choke rod that goes to the by metal spring to make the butterfly open". The choke spring, even if intake mounted, was designed to close the choke plate when cold to richen the air/fuel mixture. IF the person changes the length of the choke spring rod to hold the choke plate open, this defeats the purpose of the choke. When Cold, the rod, attached to the bi-metal spring in the intake, should "close" the choke plate to a light pressure. When the motor starts, I am positive the marine carb would also have a choke pull off used to slightly pull the plate open. As the bi-metal spring heats, the pesssure on the plate will weaken and the plate should be pulled to the full open position. Unless I totally misunderstand what you were implying.
I am not a marine mechanic, which is why I signed up to share information. However, I do ahve a good understanding and knowledge of carburetors and chokes. Just trying to share my experience.

You are not misunderstanding me, We both have a good understanding but the boat owner probably does not.

Yes the choke should "snap" shut when the throttle is activated and YES the choke pull off should open the butterfly about 1/8 inch.

But trying to explain in detail how to adjust a choke to someone who may be a novice can be difficult.
I find it best to round off the explanation a bit so as not to confuse someone who may not fully understand.

The difference between a MARINE carb and a AUTO carb is,

NO vacuum ports, NO high idle cam on throttle. (the throttle lever is how high speed cold start up is controlled) When starting a carbed motor one should advance the throttle so the motor runs at about 1500 or so rpms for a good 30 -60 seconds to allow for initial warm up.

Basically that's it.

With out any photos of the carb we can not assume it is set up right, A lot of boat owners make adjustments without fully understanding what they are adjusting.

I did include in my previous post what the merc manual says on adjusting the choke...

Thank you. Now I know a little more on marine carbs and I understand your point.

Oh if you were confused about something I typed such as open or closed being used wrongly...

Keyboard cowboys make many typos................me too,

sometimes I think a whole lot faster than I type and it does not always come out right..that's why there are others to correct me...

Yes I said open but meant,

""""slightly closed vs snap shut if need be in order to allow for full opening when warm""""

Kinda what it should have read like. Hard to put into words sometimes. Obviously the choke should snap shut, the bymetal spring should travel enough to open it all the way when warm. BUT maybe he has other issues like a clogged crossover.........bad bymetal spring, maybe someone hacked at it before.........only he knows these things and maybe he does not understand what to look for......
Also I reply to this site when at work and sometimes have several other things going on and I am not 100% focused on
my answers. depends what my work load is and how many cups of coffee I have had.

Sometimes I need several to get my head working right...........

I twisted wrenches most of my life, not typed on a keyboard or anything else.

just sayin........

Pardon the pun, but I am in the same boat!

Thank you all for your help

khghost;- sorry I forgot to say the choke is the manual bymetal type and the photos you posted are fine. Thanks for all the info.
crankbait;- I'll post a photo if still needed

Hope the attached photos help. I took 3 but ony 1 would upload(naturally the worst one)

Thats a 4MV styled quadrajet with a divorced choke setup.

As shown by the attachment kghost put up, you only have two "choke" adjustments.