The Stovebolt Site Forums The Shop Area Engine Shop Rochester B idle speed connection/operation

Hi - I'm working on a 48 Fleetline with a Rochester B carb. The idle speed adjustment doesn't seem to stay - as soon as the accelerator pump linkage is moved the cam looking piece (1/4 round piece with the ridged on the edge) tends to rotate down, changing the idle speed. I'm hoping someone can explain the idle speed cam connection and operation. I'm wondering if there is a piece or connection missing (spring, etc) - I don't see this particular type of adjustment mechanism in the Chevy shop manual or any other Rochester B picture/video I've seen. Not sure if the screw connecting the cam to the carb is supposed to tighten to keep the adjustment or what but looks like the prior owner tried to spot weld the cam to the screw (note the small blob of metal on the cam) so it can't be tightened... Any help appreciated!

Thanks!

It looks like you're missing the fast idle link between the choke linkage and the throttle. There's a picture of that link in the 1948-1951 Truck shop manual on page 6-60, although it looks a little different than yours. There should be some kind of link or rod between choke and throttle mechanism.
A PM to carbking here would probably sort out your issue. As his username says, he's the carburetor expert.

Looks like you have a 235 carburetor on a 216, judging from the carb flange hanging over the edge of the manifold, exposing the wider space hole of the 235 Model B.
You may want to save yourself some big headaches and start with the correct carburetor for a 216 that's complete, in better condition, and all there.

Isn’t the bolt spacing different for 216 vs 235 carbs?
I tried but can’t swap my 216 and 235 carbs on my trucks
I had to borrow the whole manifold to move the 216 carb onto my donor 235 engine that I wanted to use in my 50
So not sure how one could mix that carb to engine without being very intent on trying it

Edit: I think I see what you mean, the carb is modified to fit the different spacing
I get it
-s

If you want a quick fix you can take the cam screw out & put a washer behind it. That will lock up the cam & then adjust the idle speed the way you want it.
It is supposed to have a rod connecting the cam to the choke lever as previously stated. That is supposed to raise the idle speed when the choke is closed.

George

You could just let the fast idle cam fall to its natural gravity induced position, adjust the hot idle and let it go for now. Without the linkage in place, you won't have fast idle when applying choke.

Some people elongate the holes in the carburetor base to enable it to fit.

You may look into Mike’s Carburetor website or YouTube videos. He rebuilds these make and model carburetors. Here is my B carb on our 1948 3100 Chevy Truck install on our 216 engine

Thanks everyone for the great input and ideas, I appreciate it! Guess we'll have to rig up something to make the idle cam linkage or make it not matter (adjust for it in it's static position) as suggested. The previous owner, for whatever reason, decided to try to spot weld the screw holding the cam on but it didn't stay. My shop manual must be for a different carb, which makes sense if this is for a 235 as you guys suggest. I've attached it... I guess I'll try to find a diagram on line of this particular carb unless someone has one they can share - much appreciated!! Thanks again!

Thanks, yes I've used mike's videos when rebuilding this carb. Yours seems a bit different as I don't see the same idle cam as on mine.. Maybe because as others are suggesting, it's been replaced from a 235...

You will have to have the cam there as it serves as the idle stop.

George

jeffbanjo -- The original carburetor on a 1948 216 would be a Carter type W-1 model number 574s.

As GM owned Rochester (first single barrel carb in 1950), the Chevrolet parts manuals printed after 1950 suggested the Rochester as a factory service carb. This is why the information in your manual differs from the carburetor you have.

(Opinion) the Carter W-1 is a vastly superior carburetor to the Rochester model B.

Jon

The picture of a 235 carb in the 1955.2 truck shop manual shows the same beefy link as TexasA&M’s picture. Maybe it’s not for a truck?

He said he's working on a Fleetline, which is a car.

Otto, as long as this thread sticks to a 216 engine (shared in our trucks), it is OK. If it drifts to the car, it will get moved to the Greasy Spoon.

I know. I was answering Kevin's question about the possibility that the the linkage may not be for a truck.

Thanks carbking and everyone - think we'll just rig something after adjusting to hold the cam in place then ultimately probably replace the carb... My 46 1/2 ton had a Carter W1 and I agree - it worked much better...

Thanks again, all for your help!

Jeff

Jeff you can use a common brazing rod or even a more common metal coat hanger to make a link for this. Good luck!