VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 1930 updraft carb observations

I decided to look inside my carb. today as it seems a little lean at part throttle.

I found a few things I don't understand.

1. The fuel metering rod is much smaller than the ID of the vertical jet.

2. The holes in the vertical jet are spaced much further apart than the total travel of the metering rod.

3. The metering rod protrudes way below the bottom of the vertical jet.

I assume all these conditions are normal. I don't really see how the movement of the metering rod does anything.

I installed a new float recently and believe setting the correct float level will correct my problem.

I'm just curious about some of the observations I made.

Thank you, Larry.

From what you describe, everything sounds normal.

Hi Larry,

I had some of the same problems with my 1930 Coupe, with poor part throttle response...must have had two different Carter carbs apart more than I care to remember. never did get any better...

But if you think about it, its entirely possible the exhaust systems we are using today may be more free flowing than what had initially been installed in 1930, or our gas is so different, that the calibrations don't work, or most likely, no matter how many times we rebuild them, the Carters are just worn out.

I then tried a Tillotson carb and had much better results, despite it being a cheaply produced replacement carb.

Finally, upon CarbKing's advice, I purchased a Zenith 14991 modern replacement updraft carb, and made up a allum spacer to fit in to the Chevy intake/exhaust mounting. This is a tunable carb where you can set the main gas circuit, allowing for changes in gasoline quality, or different exhausts...well...the performance of the engine is really wonderful. Once I set it up, its been left alone and never fails to start, idle or accelerate far better than ever before.

I believe I paid approx 260 dollars for the Zenith. Send me a pm and I can look up the vendor and send you that link.

Life is too short to drive a poorly running classic Chevy...

Jay

Since your on the cardb subject. I am "trying" to rebuild or should I say disassemble an C-rjh-08 carb. I cannot get the offset from center brass screw on the bottom of the vertical shaft loose. Is that just a brass scew the size of the threads or is there more to it. I am letting the penetrating oil sit for a long time and still wont budge. I am thinking I may have to drill it out. Also the shaft that fits into the side with a cotter pin holding the spring in place.--How do I remove that? Where can I buy these types of replacement parts?

I have pics but dont no how to load.
thanks

The screw is soldered to an 1/8" dia. brass tube that extends across the open part of the carburetor body. It must be gas tight in the bottom and top passage. Therefore it will stick into the passage. A high quality penetrating oil (PB Blaster is my favorite) will sometimes free the tube if applied to the tube inside the open part of the body several times over a few days. Warming the carburetor body will help but also weaken the solder joint. If the screw comes off the tube then a special puller is required. You don't want to try to drill out the tube. It is a really bad idea as you are almost certain to mess up the upper seal area. Needle nose pliers will just destroy the upper part of the tube.


I use a pair of arc-joint pliers to grab the arm and hammer applied to the pliers to tap it out. Misses up the pliers but since that is all that I use those pliers for is okay.


The Filling Station and a few others sell the low speed jet tube. Not aware of anyone selling the screw or choke shaft and arm. They can be fabricated at a cost. Or you can send the carburetor to a specialized rebuilder and pay a reasonable cost to have the carburetor rebuilt. Or you can send it to a carburetor repair generalist and take your chances on both quality of rebuild and cost. A local mechanic has a 90% chance of really messing up the rebuild. An amateur has a 95% chance of messing up a rebuild if it requires trying to take out any parts that are not easily removed. I have had to deal with the result way too many times.

If you feel that you have to drill out the low speed idle tube, you should probably stop what you are doing and, as Chipper suggested, send your carburetor to one of the quality carburetor rebuilders that are listed in the VCCA. Also, special Carter tools are required for the removal of the pot metal venturi and the pot metal standpipe.

Several of the parts for your carburetor are available from the Filling Station. However, other parts, such as the choke arm and shaft, are not available.

The shaft at the base where the bowl nut screws into. I was able to remove that unit. It has a tube with small holes around the shaft and secured to the base brass screw with the hollow center. Is this the shaft your talking about?

There is a solid brass screw adjacent to this shaft on the base of the carb body (where the float sits). About 5/16 in diameter and flush to the carb body. This is the one stuck! Is this soldered in?

The carb is dirty with solids. Worked fine about three years ago.

Any suggestions for a reputable rebuilder?

If it is a 1/8" diameter tube about 3" long with two holes and a swagged down section near the open end then: Yes, that is the low speed jet (aka idle tube).


That is the accelerator pump jet assembly. They are often a real bugger to remove. It is not soldered but must be removed to make sure that the opening (75 drill) is open, the ball is free to move and seals into the base. Otherwise the accelerator pump will not function properly. If you look closely you can see the jet end inside the carburetor.

Both Skipper (aka Junkyard Dog) and I can give you a quality rebuild for a reasonable cost. Of course I think I do a better job. So does Skipper.

I have all the parts removed and cleaned except for:
1.) the solid brass screw on the base (stuck)
2.) the accelerator pump unit-it is loosened.
3.) the gas shaft (cotter pin holding spring in place.
4.) the internal parts in the throat center. (some type of shaft and cone assembly)

I can reassemble (loosely) the unit and ship it out.

Brass bowl is good-like to have it polished.
Brass float is ok- may need adjustment.
I have the rebuild gasket set and leather washer for the pump.
The rubber cover for the pump may have to be replaced.

Send me a private message with a quote.
Estimate for shippping.
Thanks- jmm richmond va

OK- The stuck solid brass screw is called the "Low Speed Jet Tube" It appears to secure a hollow tube with small holes that are in a shaft to the idle mixture adjustment screw.

The question to clarify is the tube secured to the brass screw or does the screw just allow access to the tube?

I guess it could be secured with dirt, grime and varnish.
Also maybe if I remove the idle mixture screw and let the body set on its side in penetrating oil for a week or so. It may loosen things up a bit.
Any thoughts appreciated.

I can send pics but dont no how? Newbie!! Do I need to sign up for the VCCA to be able to send pics?
thanks-jmm

The slotted cap on the low speed idle tube is soldered to the tube so the cap and tube should come out as one unit. As mentioned above by Chipper, if the slotted cap comes out separately, then you will need the special Carter tool to remove the tube.

You must be a member of the VCCA to post photos.

By the way, I sent you a PM yesterday and so far you haven't read the PM.

Got it thanks! What is the turn around? jmm

From the time that I receive the carburetor to it's completion is three days or less.

Chipper rebuilt my 32 carb and it is perfect---and I thought the price was mor than fair.