The Stovebolt Site Forums The Parking Lot Early 'Bolts (1916-1936 1st Half) 1920's Chevrolet carbs

Wondering if anyone can tell me the true difference between the RXO and the RAK version? Been fighting to get and old engine running and it is a '28. It came to me with an RXO since the truck is a '26, so I assumed it must have run that way at one time. I have had two RXO's on it and it has to have the choke constantly half closed to even think about running and will not idle period. I have eliminated , I believe, everything else so now I am back to carburetors again.

Monte, there is someone on this forum that seems to be an expert in carbs. However I haven't seen him around here lately. I'm sure someone knows who he is and if they can tell you, you can PM him. Check the archives; you may find him there.

Thanks, I'll check when I have time.

carbking

The carb on my 28 is a C-RAKX-O
Thought it was original..?
When I last worked on it several years ago I couldn't adjust it how I wanted, it ran, but not as well as it should have. I asked around and looked for parts and found it was very very expensive to work on, supposedly to get it apart some parts will almost certainly break, and they were quite expensive.

Shortly after that I found some modern replacements that looked OK, not exactly original, and were pretty cheap, but I haven't bought or tried one.

I'm supposed to bring it out later this summer for a local car show, they want an old "barn fresh" car. When I got it about 7 years ago it was barn fresh from the mid 60's, now it's "barn re-freshened" for 4 or 5 years..

Curious to hear what you learn about carbs, as I'll probably have to deal with mine in a few months.

Grigg

There are a number of differences from the RX-0 to the RAKX-0 design. Among these differences:

A. Improved float and fuel valve
B. An economiser (in the RAKX-0)
C. Improvement in the size and spacing of the accelerator jets (in the main discharge nozzle).

Cast iron used on the RAKX-0 seems to be inferior to all other Carter brass bowl units. I do not know why. Often, the main housing in the area of the idle tube will deteriorate to the point of requiring metal-spray of the whole area and re-machining of the idle tube lower seat.

Idle issues with these carburetors are two-fold:

First (no offense meant) - the idle adjustment meters air, not fuel; thus in to RICHEN, out to LEAN the mixture.

Second - the idle tube on these carburetors forms its own upper seal when the tube is inserted into the carburetor. Removal of the tube and reuse will guarantee idle issues unless the tube is reformed. Carter printed often that the low speed jet should never be reused. This was good advice for the “parts replacer”; however the jet MAY be reused with some reworking. The reason that Carter suggested not to reuse the low speed jet is that the upper end of the low speed jet tube is inserted into a tapered passage. As the jet is tightened, the taper of the passage forms the upper seal for the jet. If one simply reuses the jet, the seal may not be perfect, resulting in a poor idle condition. However, one may CAREFULLY enlarge the upper diameter of the used tube by inserting a tapered object into the upper end (an icepick works). Thus the tapered passage will form a seal with the enlarged diameter.

As with the W-1 Carters, the "C" preceding the rest of the casting number simply means that this particular sample was built by Chevrolet in the Bay City plant under license from Carter.

Here is a link explaining which carburetor was original to which early Chevrolet:

http://www.thecarburetorshop.com/Kchevrolet1.htm

Note the identification numbers used in the link. While service versions of the 150s (RJH-08) were the familiar Carter triangular brass; earlier carbs were tagged with a red cardboard tag. Good luck on finding any of these intact.

Opinion - while I offer these carbs for sale, and offer repair kits and parts for the carbs; I would highly suggest these units be used ONLY on number-matching show vehicles or museum vehicles. The carbs were not really very good and are quite expensive, parts (other than a clean-out kit) are extremely expensive, and some special tools are absolutely necessary when working on the units. I would suggest more modern replacement units for those who enjoy driving the vehicles. The later 6-cylinder RJH-08 150s are somewhat better; but even with these, more enjoyment would be possible with a replacement carb.

If I owned one of these cars, it would definately be the Canadian version ☺, and thus have the Detroit carburetor, which is light years ahead of the Carters of this period.

Jon.

Thanks Jon!

That confirmed clarified, and added to what I thought I learned a few years ago.
Great info, almost like you've worked one a few

While my car is original, it's nothing special.
What do you recommend for a functional non original carburetor for a 1928 Chevy 4?
And where do I go to find one?

Thanks,
Grigg

Grieg - there are many universal replacement carburetors that have been produced through the years.

Two issues to remember:

1. The RAKX-0 is a "cross-flange" carburetor. If you draw a straight line between the two mounting bolts, that line would be "fender to fender". A "straight-flange" carburetor would have the line going "bumper to bumper". As virtually all universal carburetors are straight flange units, a 90 degree adapter will be necessary. Some vendors can supply the adapter, but one can easily be fabricated. Visualize the capital letter "H". Lay the H on its side. Rotate one of the legs of the H 90 degrees. Drill holes in the 4 ends of the H which have the same dimension as the flange bolts. Install the H between the intake manifold and the carburetor, and you have rotated the carburetor hookup 90 degrees.

2. Virtually all replacement carburetors are set up for an electric fuel pump of 2~4 psi. The original was set up for a vacuum tank. The carburetor MUST be modified internally to use the vacuum tank OR an electric pump should be fitted.

Three of the more popular universal replacement carburetors are:

1. Zenith 68 series
2. Stromberg SF and SFM series
3. Carter BB updraft series

As all of these are made in multiple physical and airflow sizes, it is important to discuss your needs with the vendor.

Jon.

Grigg, I have a 1928 chevrolet truck engine in my vintage dragster. My father built it back in 1960. It has international KB5 truck pistons, a full race cam that was reground by fenton. It had dual carbs on a manifold that he built for it. The carbs were screwed up from a guy that bought it from my father.(that I bought it back from) so I built a down flow intake and used a holley 2BB bug spray carb. It looks like a old holly but has plugs on the side so you can change main jets. I used a VW bug intake that I got with the carb to adapt it to the 28 chevy manifold. It was very easy to build and I got the intake and carb at a swap meet for $25. You could do something like that and get a newer model carb on that engine. I could e mail you a picture if you would like to see what I did.

Think I'm going to post a video of how this thing runs on u-tube or similar and see if anybody has any ideas.

Well, I have no problems making an adapter if needed. What's the harm in not using an adapter, difficult to fit air cleaner under hood side panel, and linkage changes?

I have a downdraft Zenith with the same bolt pattern, and the 28 manifold is reversible to make it a down draft manifold. I have no idea if the carb is a good match for the engine, but would be easy enough to try, it does have an adjustable main jet.

But a better solution would be something that bolts on with very little modification. This is a car I only take out for parades, an occasional local show, and nothing in the last few years.

If I found a simple to swap and economical carburetor I'd give it a try, but for the use it gets it's not worth spending much money on.
I probably sound really cheap, and sometimes I am. This car is not my priority right now, however I've been talked into dragging it out of the shed and convincing it to run in the next few months.
Just considering my options, remembering the carb was somewhat of a problem last time I played with it.

Grigg

Just resurrecting this thread, and moving it, for reference.

Just received an RX-O carb from John Lucas/27Capitol and was doing research.

Grigg hasn't been with us online in awhile, but we did see him in Winchester last year. I wonder if he still has that '28??

I wish I'd seen this thread back in 2009.. @28chevys in the off chance you see this, I'd like to see pics or vids of the vintage dragster with what sounds like a '28 Chevy four banger in it (if I'm reading the thread correctly). I don't own anything like this, it would just be cool to see.