What is the MPG difference between the Holley 1920 with California Emission and without?

Also, do you see the image in my signature? On my computer it shows as an error image. If you copy the location in the address bar it shows up, if you're in firefox right click on it and click view image and it will show up.

Not enough info and too many variables to answer the question as asked. Info needed includes year(s) of engine(s) being compared; year(s), mileage(s) and model(s) of vehicles being compared, transmission type(s), specific carburetor number(s) being compared, history and condition of carb(s). Variables include state(s) of tune, presence/absence/adjustment of various emission devices, driving conditions, etc.

broken-image icon in your .sig ; can see the pick with right-click and "view image". Think your .signature markup code is not quite right.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I meant the 1920 model holley carburetor. One includes california emission and one doesn't. Not sure what they did to the california emission one, but I bet it lowers gas efficiency, that is what I'm wondering.

1920 is not the carburetor number, it's the carburetor model. There were between 6 and 10 different Holley 1920s used for each of eleven model years' production (1962 to 1973), plus 10 different aftermarket replacement 1920s. Grand total of roughly one hundred different 1920s! Many design aspects and features came, changed, and went during that timeframe. That's why your question is not specific enough to answer yet. If you actually have the two carburetors (and it sounds like you do) then you can find the carburetor numbers by looking at the flat surface of the carb casting, above the fuel inlet fitting. The carb number is four digits, sometimes followed by one or more letters. For example, "2372A".

When you say "one includes CA emissions", what exactly do you mean?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

damn, didn't realize

64-3114 and 64-3112
reman part number

Nope, those aren't carburetor spec numbers. They are "remanufacturer's" sales numbers. "Remanufacturer" in scarequotes because "remanufactured" carbs are generally trash. These 64- numbers are Holley II numbers, and Holley II is among the less bad of the "remanufacturing" outfits, but they still don't tell us what carbs you're working with. Look closely in the area indicated by the green arrow in this photo, and you'll find a 4-digit number with an "R" before it and possibly some letters after it. Those are the numbers needed to ID the carb. Also still waiting for what you mean by "one of them includes CA emissions". Please, I'm trying to help...will you help me help you, by providing all the information that's requested of you?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

never mind, they have different applications, one it for california emission cars, and one isn't. Thats the difference

I dont actually have the carburetors, I was researching on them. R4351 - R4355 is the range of carb numbers that those two reman numbers match with.

my current carb is a 12R-7611B, I get poor milage (11-12MPG) and hesitation on acceleration. accelerator pump works. I read in here of people switching to holley 1920s and getting electronic ignition. So I'm going to try that.

nm

Nope...that's a casting number! It can get confusing with all the different numbers associated with just one carburetor.
You can (and probably should) try rebuilding your carburetor and installing a new float—you're likely to have better luck going this route than by buying a "remanufactured" unit — but in the end you may find it is time for a new carburetor.
You've already got a Holley 1920. If it is time for a new carburetor, there are various 1bbl options as well as the popular and beneficial 2bbl conversion. There's a great deal of help available here on the forum for whichever route you decide to go.
Definitely a good swap, but you'll probably find it best to tackle one problem at a time and get the carburetion all sorted out before adding additional projects to the mix.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I just realized I had a 1920. I'm not the greatest when it comes to carbs, never worked on one.

how full should the bowl be when the cover is taken off?

Well...when you take the bowl off, it'll be immediately empty!

You really should not attempt to disassemble or work on the carb before you order and read the three books described in this post. There are a lot of small parts and fine adjustments, and it's very easy to make the situation worse rather than better.

If you decide you want to buy a brand-new carburetor instead, send me a PM (private message).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.