Holley 1940 Carburetor

Holley 1940 Carburetor

The Holley 1940 carburetor uses a Nitropyl type of float and because they tend to absorb fuel over time, we recommend that they be replaced at each carburetor rebuild. Once a Nitrophyl float has absorbed fuel it will become too heavy and allow more fuel to enter the bowl than what is needed, causing a flooding effect.

The Nitrophyl float can be identified by the black color and it looks like it is made of a plastic material.

We now have the brass replacement floats for the Holley 1940.Holley 1940 Float


 Holley 1940 Questions & Answers

Need to compare what is inside our Holley 1940 carburetor kits? Watch this video.


Holley 1940 Check WeightHolley 1940 Check Weight

This is the Holley 1940 check weight. These are not produced and if you lose your check weight, then your choices are to find a donor carburetor, or make your own. This one is a bit harder than most because it is a hex shaped weight. I would say the most important spec is the weight. Too much weight and the check ball will not lift as it should.

Here are the specifications.


1 gram in weight

7/16″ long

5/32″ wide, point to point of the hex.


Watch a video about the Holley 1940 accelerator pump.

  Holley 1940 Carburetor

Holley 1920, 1940, 1945, 2210, 2245, 5200, 5210, 5300 Carburetor Manual

Holley 1940 Carburetor Manual

Holley 1940 Throttle Body Bushing Replacement

When the Holley 1940 carburetor throttle shaft gets .010 or more of wear, it is time to add bushings to the throttle body. Without a run-out mike this might be difficult to measure, so estimate anything over 1/32″ in sideways action. When the throttle shaft is too loose it will cause a vacuum leak, which will make the engine idle rough. Besides measuring you can test this situation by spraying carburetor cleaner around the throttle shaft while the engine is running. If the rough idle smooths out, then you need to re-bush.

Holley 1940 Bushing

If you don’t think you have the expertise to tackle a job like this, then you should take it to a machine shop, otherwise here is one way you can accomplish this without having to have a lot of sophisticated machinery.

The bushings required can be found in our Holley 1940 carburetor parts catalog.You will need to order two bushings.

Carefully ream out the hole so that the new bushing will fit. Use an expandable reamer HS 6A. It needs to expand to at least .345″. You want to ream the hole until the bushing fits into it tightly. Not so tight that you have to beat it in, but it should take some pressure. If you get it too tight and have to beat it in place, the bushing will reduce down and the throttle shaft might not turn as freely as it should. You can add a bit of JB Weld around the outside of the bushing to make sure it stays put, but with the right fit you will not have to do this. Once you get the bushing in grind down anything that is sticking out so that the bushing is flush with the throttle body.

That is it. Replace the throttle shaft and you are on the way. Take your time, because it doesn’t take much of a mistake to ruin the throttle body.

Holley 1940 Rebuild Video



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Choke Types

We have 4 different types of chokes, Intregal, Divorced, Electric & Electric Conversion.

Intregal Choke

Integral ChokeThe integral choke is mounted on the carburetor, either near the top, or near the bottom. The illustration shows the choke mounted on the top of the carburetor. The thermostat is heated by a heat tube that runs down to the exhaust manifold. The heat tubes heats up the thermostat and moves the choke valve to the open position. A vacuum passage in the carburetor feeds up to the choke housing and helps pull in the heat from the heat tube. Some of these chokes will also have a hot water jacket running through, or on the thermostat to facilitate heating.

Divorced Choke

Divorced ChokeThe divorced choke typs has the thermostat mounted in the intake manifold instead of on the carburetor. In this illustration, the arrow points to the thermostat which is covered by a metal shield. A rod connects the thermostat to the choke lever, which controls the choke valve to be opened, or closed. As the intake manifold heats up, the thermostat mounted, expands, opening the choke valve.


Electric Choke


Electric ChokeThis is a typical electric choke mounted on the carburetor, which is integral. In this case there is one wire on the choke thermostat. This is the 12v source, which all electric chokes use. The thermostat is grounded via the carburetor itself. Some electric chokes will have a 2nd wire (ground wire), which is connected back to the carburetor. When the key is on the thermostat is heated up, opening the choke valve.

Electric Choke Conversion


Electric Choke ConversionThis is a typical electric choke conversion kit. This is used to convert an integral, or a divorced choke to an electric choke. These choke kits come with a temperature sensor that bolts on to the intake manifold, which provides more accurate choke control than with an electric choke without the gauge. The electric choke conversion kit is not used for a manual choke conversion. The choke housing must be in place in order for it to work.
This choke installs in 20 minutes or less with no special
tools. Remove the old choke thermostat and replace with this choke conversion kit.
Attach the temperature sensor under an existing engine bolt.
Wire the positive wire into the vehicles electrical system. Ground the choke to the carburetor.
Complete instructions are provided for each application.


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