Holley 1904 Technical

The Holley 1904 is a 1 barrel, downdraft carburetor and has three basic parts, the main body, throttle body and the float bowl. The main body includes the metering block, float and the economizer. The float bowl mounts on the front of the carburetor and can be metal, or glass. The glass bowl is becoming a rare piece to find, undoubtedly because they are so easy to break and they are not made any more.

Having the float bowl on the front allowed the 1904 carburetor to be designed with a low profile, which accommodated a smaller space between the engine and the hood. While we are fortunate to have carburetor kit coverage for all of the 1904 carburetor numbers, there are few other parts still available. In particular the float and the plastic actuator are very rare these days. We get quite a few requests for these parts, but when we do find these parts, they generally go on other 1904 carburetors. Your best bet to obtain these parts is to find a used carburetor and use it for a parts donor.

Holley 1904 Carburetor Manual

There are some common problems with this carburetor and fortunately we know what they are and how to fix them. Because of over tightening of the float bowl screws, the main body is often warped causing leaks around the float bowl. This can be rectified by heating the body in a vice and straightening the mounts. Another common problem is fuel leaking past the needle & seat, causing a flooding condition and we have a process that will take care of this problem also. Due to years of wear the choke shaft often has excessive end play causing the idle screw to miss the fast idle cam and possibly cause the choke valve to hang. Last but not least is a problem with the metering block being warped and allowing fuel to leak past. This can be rectified by grinding the surface flat, which we do with a disk sander, but a flat file should also work. All of these problems are fixable and we have the cures, which are detailed on our Holley 1904 technical page and on our many Holley 1904 videos. It would be a good idea to review all of this information before jumping in to your rebuild.

Please be aware that any of our technical information is based on parts that you have purchased from us. Parts from other sources may install, or work differently.



Float Bowl Leak

Most 1904 carburetor these days have warped bodies where the float bowl attaches. The biggest problem with the fit of the 1904 float bowl is not the bowl itself. Rather, it is the presence of so much warpage in the main body surface to which the bowl mounts. I know of no other way to fix this than the way that I use: put the main body in a press, heat it up and press straight the "ears" to which the bowl mounts. Yes, after I get it as straight as it is going to be I dress the gasket with some Permatex Anaerobic Gasket Maker, but that will do you little good without a reasonable straight main body.

Use this cork gasket when you have a warped carburetor.

Watch a video about fixing the Holley 1904 float bowl leak.


Vacuum Check Ball

The 1904 carburetors for automatic transmissions have a nylon check ball and retainer clip that goes in the float bowl body where the throttle body mounts to the float bowl. The manual transmissions did not need this. In our Holley kit # K421, this check ball is plastic. This vacuum port is used to feed the distributor advance vacuum line.

Helpful Documents
Holley 1904 Carburetor Identification, Parts List & Specifications.

I.H.C. 4 Cyl. Metro & Scout Holley 1904-G

Installing the Needle & Seat The 1904 tends to leak past the copper washer between the seat and the bowl. When installing the needle & seat apply a small amount of Permatex Red to the threads of the fuel inlet screw (the screw that holds the seat). Also apply a very small amount of Permatex Anaerobic gasket maker to the washer (some are copper, some are fiber).

1904 Float Bowl The Holley 1904 glass float bowl and metal float bowl are interchangeable. The glass type of float bowl uses special screw clips. You must use these on the glass bowl, or it could break.

The Holley 1920 float bowl will also work on the 1904, but the baffle will need to be removed 1st. The baffle simply slides in and out.


Adjusting the Accelerator Pump Stroke for Seasonal or Climatic Changes.

The accelerating pump stroke can be adjusted for seasonal or climatic changes by changing the position of the pump link in the throttle lever. The hole in the lever nearest the throttle shaft is the normal setting and should be satisfactory for nearly all operating conditions. If a richer accelerating pump discharge is desired for extreme cold weather operation, set the pump link in the outer hole in the throttle lever. Pump link position can be changed by removing the cotter pin at the lower end of the pump link, moving the pump link to the other hole, and re-installing the cotter pin.

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What is the hole in the bottom of the flange for?

This hole feeds the vacuum channel up through the carburetor and feeds the distributor vacuum advance. If your distributor connects to this vacuum port, then you need to make sure the hole has access to the manifold vacuum. Either line up the gasket hole, or cut a slot into the gasket from where the hole is to the center. This will give the vacuum a channel to follow.