What makes a carburetor design for automatics vs manual??

[Moparfiend]

Speaking Holley only.

I have seen some carburetors called-“automatic” ie automatic carburetor in for sale areas. Wondering what that means?

I understand that a mechanical secondary is better for a manual transmission and a vacuum secondary is better for an automatic generally and that tuning would be different but is there anything else inherent in the design that’s different?

 

[Dave6T4]

Might be slight jetting changes. Maybe a little richer on a 4-speed.

 

[rickseeman]

It might be the way the linkage is.

 

[44070dart]

Wouldn't the accelerator pump be different also, with the automatic one a little richer

 

[R413]

Holley for 1970. Only difference is choke settings. They don't list RPM, just settings, seems a bit odd. They are all vacuum secondary.

 

[RemCharger]

I'm wondering about dashpots. Do people run without them in 4 speeds? Good/ bad/ necessary?

 

[R413]

If you look on the specs there are metering differences and choke settings. And the idle and or fast idle speeds can be are higher for manuals because they aren't going to slam into gear.

Manuals have a different throttle stud installed. Some manuals have a dash pot.

A 1967 440 HP manual has a different choke pulloff. Don't know why.

Remember the different part numbers are so that unit is ready to install and go without tuning on it. They are building how many cars per day?

Look at different years and carb models and some are very different some have the same specs.

See chart below, the 1970 440 HP 4 speed carb on the right side has different low speed jets and step up rods, higher float level and different choke settings, idle and fast idle RPM are higher.

Same throttle bore size and Venturi soze. They don't mention the air bleeds and accelerator pump size.

 

[toolmanmike]

D All of the above.

 

[R413]

I'm wondering about dashpots. Do people run without them in 4 speeds? Good/ bad/ necessary?

What they do is prevent the engine from dying when you quickly take your foot off the gas. Maybe in certain conditions they are needed, but usually not necessary.

Remember it's all about happy customers and the warranty period. Dealers never want the engine quitting while driving, especially with power brakes and steering and a 100 lb weakling driving in the city traffic.

 

[Don Frelier]

What they do is prevent the engine from dying when you quickly take your foot off the gas. Maybe in certain conditions they are needed, but usually not necessary.

Remember it's all about happy customers and the warranty period. Dealers never want the engine quitting while driving, especially with power brakes and steering and a 100 lb weakling driving in the city traffic.

Now we have cars that quit at a stoplight, and that's a "feature".
(Sorry if I'm getting off topic)

 

[66 Sat]

Now we have cars that quit at a stoplight, and that's a "feature".
(Sorry if I'm getting off topic)

First thing I switch off in my wife's car - I can't stand it. Apart from the stress on the starter & battery, I hate the slight delay when it starts and takes off, and it always feels like there's something wrong with the car when it just cuts out like that.

 

[Geoff 2]

Can anybody see the 'oddity' in the chart in post #7?

A lot of people think that when you fit a carb to a larger engine, you need larger jets. The 440 carb has smaller sec jets than the 383.

 

[Dragon Slayer]

Normally there is an Idle jet difference. Also, the SVM does not give you the meter block data; and can have errors. A holley book would tell you what is different and that can lead to differences in air bleed size. Carb calibration is more than just fuel jet size. Carter typically had an idle jet change, accelerator pump change, and then the venturi could be different with bleeds and distribution tabs. Also a choke setting difference. In today world the carbs are more generic.

 

[lewtot184]

calibration