Carburetor 2024

12/17/2023 to 2/11/2024

When I was working on the brakes I found that the car would not idle. Stalled every time. It has been nearly 20 years (!!!) since I rebuilt the carb back in 2005 so I took it out to examine. This is going to be a long post, so buckle up.

It does not look bad for 20 years, let’s see what is going on inside.
I pulled the float bowl cover off and found hard gaskets, a torn accelerator pump, and some bits of rubber in the float bowl. I think it is time for a rebuild. I have rebuilt a few carbs, including this one, but I don’t enjoy the process. I decided that if I could get it rebuilt for $300 I would pay someone else to do it. I had a Rochester 2bbl rebuilt by National Carburetors a few years ago and it was perfect so I checked with them. Price with shipping came to a bit more than $300, but I decided to go for it.
They were shut down over Christmas so it was the second week in January before I got it back. And it looks good. All the plated parts were replated (including screws!) and the parts were all polished. I was a little excited so I put it back on the car.

It was good news/bad news. Good news was the car started and ran like a dream. Bad news was I had no fast idle and the car was really hard to start when hot. Before I diddled with it I got in touch with National. I send them some videos of how the car started and ran and they suggested adjusting the choke. OK!

Here is where I started to find problems. When I went to adjust the choke I realized the cap on the choke thermostat was broken and the hole for the hold-down screw in the picture is stripped. If you look back at the first picture of the carb it was certainly not broken, but you can see the damage in my unboxing picture. Disappointing. At that point I stopped messing with it and pulled the carb out again to take a closer look.
On the bench it was obvious the upper right screw and hold-down were not doing much. Let’s tear in. Remember, the entire point of paying the money is I don’t like working on carbs…
Once I took the thermostat off I found this nicely replated cover plate. One screw removes it. That arm sticking out hooks onto the bimetallic coil in the broken-ass choke cover.
Here is the stripped hole. Threads are just in gone in half the hole. I think it was over-tightened. This carb is cast zinc and VERY soft metal, you have to be super careful.
Here is what the choke mechanism looks like. I spent about an hour trying to figure out why it would not latch into fast idle. The service manual was confusing and did not help.
Finally, I pulled out my father’s old Motor’s manual from 1951 and that cleared things up. I realized the fast idle cam is supposed to move down but was not.
In this video you can see what I am talking about. I can move the fast idle cam with my finger but it is binding and the spring cannot move it. I decided to take the choke apart to figure it out.

First step is to remove the choke plate. Notice the screws are dirty and there is some dirt under where the screw heads were.

The choke trip lever just pulls out. Then you can rotate the choke shaft enough for the choke piston to come out of the bore.

Then you can unhook the fast idle cam spring and the choke shaft slides out. Notice how dirty it is where the choke plate attached. The rest of the part is pristine but that could that much stuff get in there in less than an hour of run time?
I neglected to take a picture of the fast idle cam before I pulled it out but you can see there is carbon or something in the bushing and on the back of the cam. There was also gunk on the boss it turns on. I cleaned it up with acetone. There was also gunk (but not as much) in the bushings the choke shaft turns in.
I removed the dust cover in order better clean the choke bushings. The screw felt strange coming out and pulled out with several threads attached to it. Dammit! There are still some threads in there but I know this was not screwed up when I shipped this carb out. So the score stands two stripped holes and a broken choke cap.
Sorry for the fuzzy picture, but this is what I got off the cam, shaft bushings, and cam boss. This stuff should be CLEAN.
When I put the fast idle cam, choke shaft, and plate back together it works like this now. Much better. All I did was clean everything…
I put the rest of the linkage together and tested it. The choke is open. Since the spring on the fast idle cam is attached to the choke the cam “A” is pulled up and out of the way. That allows the lower end of the fast idle link “B” to move up so the throttle can close to the slow idle stop “C”.
This picture is not great but here fast idle is set. The choke is closed, relaxing the spring pressure on the fast idle cam. The cam has fallen down to position “A” where it forces down the choke trip lever down which keeps the fast idle link from rising at “B”. That forces the throttle slightly open, see the gap at “C”.
Now I can check the choke adjustments. First is the fast idle. With the choke closed and fast idle set the throttle plate should be open 0.054″. I don’t have anything that diameter but a #54 drill bit is 0.055″ and a #55 is 0.052″ so I can make that work.
As it turns out the fast idle position was fine. I also checked the choke pull-off (or unloader) but neglected to take a picture. There should be a 3/16″ gap between the choke body and the choke plate with the throttle wide open. Mine is a little bigger but that should not be critical. Finally I adjusted the choke. I got the stripped screw to hold a little bit. Once I am happy with this thing I will fix it with JB Weld. It does not have to be that strong. The choke cap will leak but nothing I can do about that now.
I installed the carb (third time if you lost count) and tried it. Fast idle works perfectly. I drove the car around a bit then adjusted the idle and idle mixture. The idle mixture was WAY rich. It starts a lot better hot. We are getting close.

I detailed everything I found and sent it to National Carburetors. After a week I contacted them them again a bit more aggressively. They then responded and were apologetic but said all I could do was send the carb back to them. I don’t think so. I am disappointed but we will see what they can do for me. Shit happens and everyone can have a bad day but there seems to be careless damage and poor work here. Now I have to clean up the mess. More to come…


Carburetor 2024 — 1 Comment

  1. Pingback: New(er) front brake shoes | 1941 Studebaker Champion

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