SU carburetors

[Michael Oritt]

What is the difference between SU HD6's and SU HS6's?

 

[DART]

Michael- I "think" the s means side and the d means down. Just don't ask me which the 2 on the SP are.

 

[Dave Russell]

Perhaps it would be easier to go here:
https://www.mossmotors.com/Browse/PlateMe...&ComponentID=12
And compare the two types.

Basically, the HS has a float chamber that has it's outlet connected via a flexible tube/main jet to the carb body.

The HD has a float chamber/jet that is rigidly connected to the carb body. The bottom of the jet is sealed by a diaphragm.

Hard to explain but the pics help.

HS means "Separate", HD means "Diaphragm".
D

 

[Randy Forbes]

Yeah, HD means you get to change a diaphragm; almost guaranteed if the car has been laid up for any amount of time.

 

[vette]

I don't know what the letter designations mean off hand, but the the HD carbs have the jet centered in a diaphram as Dave Russell mentioned in which the jet is adjusted via a straight slotted screw facing up on the side of the carb and all other SUs that i know of the jet is adjusted via the centering nut on the bottom of the carb. The HD carbs also idle the engine on an idle circuit which is adjusted by another screw that closes off a passage around the throttle plates which are to stay closed at idle. All the other SUs the idle is adjusted by openning the throttle alittle. When adjusting the HD carbs, you'll notice that all your adjustments can readily be done with slotted screw driver in hand and from the top of the carb.

 

[vette]

I just looked into some of my notes from years ago, and it says, 'H' = Horizontal Draft. The numerical value associated with the carb is the number of units of 1/8th inch above one inch. Hence an HS6 carb has a throat size of 1 3/4". The HD-8 is 2". I know that is true because I have HD-8's on my car.