Reproduction Parts for 1916-1964 Chevrolet Passenger Cars & 1918-1987 Chevrolet & GMC Trucks


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Shade Tree Mechanic
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Shade Tree Mechanic
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Having trouble this spring with the carburetor. The needle was struck down and not allowing gas to get in the bowl. I took the carb apart and cleaned the seat. When I put it back together the bowl overflowed with gas. I took it apart again moved the needle down and the gas didn't overflow. I think the problem I am now having is the float is not in the right position. How far should the tip of the needle be from the base of the collar? Or maybe you measure from the top of the collar to the top of the needle? I would like to know so I can then pinch the collar so it closes tight on the needle. I think the needle maybe moving to freely in the collar. Thanks Mike

Filling Station - Chevrolet & GMC Reproduction Parts


Filling Station


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Backyard Mechanic
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I had similar problems, but my 1922 has a Zenith O4 carburetor. On the outside of the bowl house (?) is a very tiny scratch (or score?), almost invisible before cleaning, indicating correct fuel level. In the Repair Manual is a picture of a very special tool with a glass tube showing the inside fuel level. I made a simple tool, with a plastic hose. If the T4 has the same type of indicaton on the outside, let me know and I can post a couple of pictures. By the way, I bought a renovation set, with seat, needle an a couple of sealings. Has worked fine for 15 years.


Per-Åke Larsson
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The fuel level is approximately 1/2 the height of the float bowl. The float was soldered to the needle which can be carefully redone. Use the lowest melting solder and an iron on the needle so you don't melt the solder that holds the float together with too much heat. A small amount of epoxy like J B Weld can also be used. Be sure to get as close to 50:50 as you can so it will be gasoline (with or without alcohol) resistant. A drop of gas tank sealer will also hold the float in position.


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Shade Tree Mechanic
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Ok thanks. Will give it a try.

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Oh My oh my did I mess up! The Zenith T-4 float slides up and down the shaft of the needle. A collar on the needle shaft lines up with one end of levers supported on the fuel bowl lid. The float pushes up on the other end of the lever pushing the needle down. Of course when the float goes down the needle is lifted up allowing fuel to flow into the bowl. The collar is held be crimping four "fingers" against the needle shaft and secured by a drop of solder.

The specified fuel level is approximately in the middle of the fuel bowl.


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Have a couple of photos of a 1921 Zenith T-4 brochure.

Attached Images
Attached PDF document
Zenith T-4 page 2 - 3.pdf (1.66 MB, 80 downloads)
Attached PDF document
Zenith T-4 page 1 - 4.pdf (1.83 MB, 66 downloads)

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In a book I have it says that there is a horizontal level line in the bowl. It also states that the only adjustment which might be useful is the idling adjustment. There is a description of the operation and adjustments and the same photo Chipper posted. " Idling adjustment tube P1 , which is permanently assembled to idling jet P , screws into the idling tube and is screwed up or down to secure the proper adjustment for idling the motor". Went to a car flea market this past weekend and purchased 5 books titled " Automobile Engineering" by the American Technical Society dated 1923. This is the first time I have opened one other than when purchasing.


Steve D
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Looking at the picture of the T4 that Chipper posted it seems that it is very similar to the O4.
So I attach two pages from the ”Chevrolet repair manual 1918-1924” and two pictures of my quite simple tool to check the fuel level. On the close up picture you have to take a close look too see the tiny ”Fuel level line” on the outside of the bowl. It is a little easier to see the fuel level in the plastic hose, even if the plastic hose is not ideal to identify the correct level. For me it took a number of soldering and resoldering of the collar before I was satisfied. On the overview picture it is me pouring fuel in the test tank – 15 years ago.
I bought the repair kit from The Carburetor Shop.

Attached Images
Attached PDF document
Testing_and setting_fuel_levels.pdf (620.21 KB, 91 downloads)
Attached PDF document
Needle_valve_adjustment.pdf (696.91 KB, 50 downloads)
IMG_5510_Homemade tool_close_up.jpg IMG_5506_homemade_tool_overwiev.jpg

Per-Åke Larsson
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The Zenith T-4 is basically the same dimensions as the O-4. So are the T-4X and T-4XF. Use the same metering jets and arm layout. Basic difference is the bodies are now have cast iron and brass pieces. I suspect that was to make them less expensive to manufacture. However with a die-cast venturi more susceptible to damage from expanding die-cast pieces. In the last 100 years the majority of the cast iron throats have cracked as the corroding venturis expanded. Good news is that in many cases the throats can be brazed back together and a brass or aluminum venturi substituted.

As an aside, that was the time when Chevrolet was considering using carburetors from other manufacturers ie: Carter, Holley, Stewart, etc. The interesting part of that process is that the earliest Carters were the RB-0 model number 32s & 33s with cast iron body and die-cast venturi in 1922-24. In 1925 they switched to RX-0 & C-RX-0 which were earlier model number 4s and 6s but had cast iron body with venturi. The late '27 Carter RAJX-0 (85s) went back to cast iron body with die-cast venturi. I have been told and read that the formula for die-cast parts had been changed to one that had much less tendency to expand.


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Shade Tree Mechanic
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Great help. Thanks Mike.

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Had the "490" for a good run yesterday it is now working fine again. I was able to set the float level with your help. We made a device similar to the one in the forum pictures to get the correct level. The biggest problem I think was the pivots that work the collar were worn in spots. Luckily we had a spare parts carburetor and were able to switch the pivots and the float moves freely up and down. Before I think it was catching stopping the float from moving. Thanks again for all your help. Mike

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Glad we could help and you now have a good running 490.


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Backyard Mechanic
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There was actually a commercial tool back in the day to aid in fuel level setting. It may be seen here:

Standard Hygrade float tool

Jon


Good carburetion is fuelish hot air

Owner, The Carburetor Shop (in Missouri)
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Shade Tree Mechanic
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Jon. Thanks for the information. A lot better looking gauge that the clear piece of plastic tubing we used. Mike

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Mike - I have collected carburetor tools for more than half a century, so obviously I had to have one.

But it probably doesn't function any better than the one you made.

I have been suggesting the clear plastic tube to enthusiasts for decades.

Jon


Good carburetion is fuelish hot air

Owner, The Carburetor Shop (in Missouri)

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