Technical Question on Tuning and Choke for Rochester 2 barrel Carb

Hi All,

I have a sbc 350 in my C10 truck with a 2 barrel rochester carb. Eventually I was thinking to upgrade to a Holley or Edelbrock but for now will ride with this.

I notice when starting up the truck if its been in my garage untouched for a while I have to feather the pedal for a good minute to two minutes. I looked at the choke setup and only see the vacuum part in the back but nothing on the side like I've seen in other photos online. Has anyone else seen this as well? It looks like the choke butterfly plate is in the open position and stays there but can't tell if someone modified to keep it like that. Would I even be able to add the remaining choke pieces (heat or electric) with my carb? I don't feel like adding manual choke, I'm fine feathering the pedal at that point.

Also given no choke how would I adjust the carb mixture screws? Would I need to do that some particular way once the vehicle is warmed up enough? I read some ways to do this include adjusting until you hear the rpm change, then doing the other one.

 

Divorced choke is missing; not sure how it even runs???

Look at the picture. There is a almost rectangular hole in the intake on the side of the carburetor with the the choke pull off. The should be a small cannister containing a spring, with a rod then connecting the spring to the choke on the carburetor.

Jon

 

Thanks I see that now! The rectangular area is recessed not an open hole. Is it just a matter of finding a divorced choke for the 2 barrel Rochester on eBay and installing it and hoping the rest of the carb works with it? I did notice the choke butterfly stuck in the open position so I guess I would need to see why that is. I’m not surprised with the crazy things the previous owner did to this truck that I had to fix.

As far as your comment on being surprised it runs at all… it seems totally fine after it warms up but I have to feather the pedal quite a bit for the first couple of minutes usually…. If the engine was warmed up enough the choke shouldn’t matter anymore for the Rochester carbs?

 

I have a '67 Corvette 327/350 and it uses the same divorced choke. If you can't find the mechanism eslewhere, the Corvette dealers have 'em, and the last time I looked, they were still pretty cheap.

 

thanks I’ll see if I can find one!

 

If the choke butterfly is wired open, then yes, it will run normally after warm-up.

There are literally tons of DIFFERENT divorced chokes. You probably do not need to be concerned about manual transmission/automatic transmission or A.C./no A.C.; but you do need to locate a choke for your year of intake manifold. And make sure when you order that you are getting the linkage rod along with the choke. Many replacement divorced chokes to NOT include the linkage rod, and yours is missing.

There are some folks that just plain do without the choke wiring it open, but as you mentioned, it can require some TLC prior to warm-up.

Jon

 

Thanks that all makes sense! I’ll look for one and install it. It can’t hurt. I don’t mind feathering the pedal but rather not have to do that so I can move it out of the garage to open air quicker.

 

Also I think adjusting the mixture screws is independent from my choke issue as long as I do it when the truck is fully warmed up?

 

I have actually made the choke rod out of a piece of coat hanger when I couldn’t find one. There should also be a sheet metal cover over the thermostatic spring on the choke.

 

To get the divorced choke to warm up properly, there is usually a heat riser in the right exhaust manifold that opens up after hot, to direct hot exhaust gasses across the intake manifold or it will take forever for the choke to fully open.
I did see one setup just recently on a 71 impala 350 2bbl carb, that was factory untouched. Instead of a heat riser in the right exhaust manifold, there was a sleeve in the right exhaust pipe at the manifold, that has a reduced ID. Maybe to direct some exhaust gasses across the manifold all the time?

Bill

 

Thanks I don’t see anything like that on the ram horn exhaust manifolds. Maybe they don’t go with the original engine and maybe since it took forever to open that’s why the previous owner removed the divorced choke and made the choke butterfly so it’s wired open (I’m assuming it’s wired open can’t tell if it is or if it’s just stuck open)

 

Who needs a choke in California.

 

haha well the truck must be from Mexico or the tropics because it needs to be babied when fired up or it will shut off even in the mostly temperate weather we get here

 

Without some means to direct hot exhaust gasses across the manifold when the engine is cold, the choke most likely will take way longer to fully open for your liking.

We see this happen when headers are installed on an engine that still has factory carb and divorced choke setup.

Probably the best way to get a choke that works is to convert it to an electric choke.

Many carb part suppliers have conversion kits.

Bill

 

Doubt there's many junkyards left around San Diego, may look at market place for someone parting out vehicles. 2bbl and intake are usually pretty cheap if not free.

Is Quadrajet stuff similar enough to use ?

 

thanks yea I should look for electric divorce choke kits if they aren’t expensive. I was hoping to switch to a 4 barrel carb eventually so don’t want to put too effort/money into the current carb.

 

Thanks yea not many junkyards left around here. Eventually I want to go to 4 barrel carb so unless there’s a cheap electric divorced choke that will work it may not be worth the effort.

 

If its electric, its not divorced.

The divorced choke coil, cover and rod are pretty expensive in reproduction.

Electric choke conversions are a little more reasonable.

Finding a usable one in a junkyard, that's correct and able to remove from a rusty manifold, may be somewhat harder.

Bill

 

Pick your poison. https://www.google.com/search?q=gm+devorced+choke+parts&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari

 

ah ok so basically an electric conversion cannot be divorced you need to start with the stock chock that attaches to the carb and convert that?

 

thanks! These could work but as others said I don’t have any heat riser so it may take a long time to open the choke butterfly. Maybe that’s more annoying than feathering the pedal hmmm…

 

Do they know what this area of the intake is for?

 

You could always put a cable operated manual choke choke on there ,simple , cheap , easy

 

Divorced means the choke element is separated from the carb.

If converted to electric, all original choke components are removed from the carb and replaced with an electric choke element that's attached to the carb and wired to an ignition on power source

There are some electric choke conversions that are still divorced, that attach to the manifold.

Depends on the carb.

 

Don't want to sidetrack the thread, but I do want to give a shout out to @carbking for so freely offering his advice and expertise. A valuable recourse for us all!@
THANKS!!!!

 

Oh yes super grateful to have experts help out an amateur like me

 

Convert it to electric choke, it will be cheaper.
And stupid easy to connect

 

Thanks but wouldn't I need another carb entirely to be able to do that?

 

Carb must be really lean to give you that much grief on warm up in SD. Is the truck from Denver , by any chance? ;-)

 

Interesting.. I wonder if I need to adjust the mixture screws? I haven't done that.. nor do I know how to haha...but I did find this:

https://itstillruns.com/adjust-twobarrel-rochester-carburetor-8016889.html

Altough the previous owner lived in San Diego the truck has been to Mexico (previous owner) and some pretty cruddy work was done to the truck there which I've mostly undone and fixed.