supercharging carb?

[SUMO]

been doing some reading [always dangerous] and have come across something that might be a problem for me - not a big one just finding another carb

im running an eaton m45 on my twin panther [when its done] order of play will be

carb through blower [sucker in this case] into engine

now i was reading that on an su type carb the slide can get cocked round in the body and stick wide open from the force of the blower - is this just a wives tale, or if you are running masses of boost or something - im not looking at running all that much...

i see the logic but havent found any hard facts yet.

just working out before i spend my sheckles on rebuilding this carb if its potentially an issue

anyone done it or had problems / success etc?

[bak189]

Don't know for a fact about the SU sticking......but Yes, we did have a problem with a slide type Delorto
and even a flat slide Mikuni......Butterfly carb. has worked best for us at 11lbs boost......you can get
a S&S Carb. cheap on E-Bay.......If you get a S&S E type Shorty you also get a accelerator circuit
make for easier start up........Great project you are doing....Good luck......

PS. Love the big Panther.....Dad had one with a chair, in the old country

[octane]

been doing some reading [always dangerous] and have come across something that might be a problem for me - not a big one just finding another carb

im running an eaton m45 on my twin panther [when its done] order of play will be

carb through blower [sucker in this case] into engine

now i was reading that on an su type carb the slide can get cocked round in the body and stick wide open from the force of the blower - is this just a wives tale, or if you are running masses of boost or something - im not looking at running all that much...

i see the logic but havent found any hard facts yet.

just working out before i spend my sheckles on rebuilding this carb if its potentially an issue

anyone done it or had problems / success etc?

LOTS and LOTS of the old European blown drag racers used SU,
and the blower/SU set-up is the standard set up for all the MG TD/TC racing boys.
Recently at the Copenhagen Classic Grand Prix I came
across these and more:












To be safe you'll need a thing like this on my carb



...a dual-cable-gas handle / two cables / a "wheel" or "rotor" on the butterfly shaft so that you can force it closed
should (what you call the 'slide' or) the vacuum piston and butterfly stick
in the open position.
It's the standard set up on the American Primo-Rivera SU carbs ,
basically Brit Burleen SU's modified for Harley use.

Check this Pdf
DUAL CABLE ROTOR AND BRACKET

(scroll down a bit.)

Actually I'd say it's an advantage to run a set-up like this as you can force it closed.
Let's say you were running a flat-slide MIKUNI or something similar,
there would be no way to force closed a sticking slide.

[SUMO]

as long as all it needs is a double throttle cable setup thats no problem at all.

looks like its been done plenty on the cars so i should be ok.

now im just reading more if i should go blow through or suck through...  watch this space, i need to learn more before i decide.

[octane]

You can't 'blow' a SU....at all.
The fundamental function of a CV ('constant velocity') carb like a SU, totally depends
on the vacuum created in the carb venturi.

Open butterfly--->create venturi vacuum effect---->lifts the vacuum piston (+attached jet-needle) up into in the vacuum bowl

Anyway a blown carb would need to be 'pressurized'
most likely in a sealed pressure box.
A sucker system will be more effective at atomizing / vaporization (spelling?) the fuel.

[SUMO]

like ive said before, superchargers are all new to me but in reading i stumbled across a few things like this

http://www.triumphexperience.com/article/how-to-blow-through-an-su.html

[55chevr]

I ran "Skinners Union" carburetors back in the 70-s on Harley's ... all the SU-s I had contained butterfly throttles behind the slides ... the slide had the needle for the mixture when not at W O T ... dont see how it sticking open would matter as the butterfly would be closed and running off the low speed circuit. The SU-s I acquired came from Jaguars ...

[Peter Jack]

Unlike a lot of the motorcycle carbs which use the slide as a throttle plate the SU only uses the slide to control mixture. On the slide throttle carburetors the slide is directly attached to the throttle cable. In the SU the slide is controlled by the pressure differential before and after the slide. The throttle plate is conventional and is controlled by either cable or linkage. It is downstream of the slide. Boy I'd like all the hours back that I spent working on SU carburetors. At the same time they were a simple and reliable devise when set up correctly and there was a wide range of available needles.

Pete

[55chevr]

PJ ---They are fairly simple but the needle makes for a lot of adjustments .. Like you I spent untold hours playing with them ...  when they are right, they are perfect

[octane]

You can't 'blow' a SU....at all.

like ive said before, superchargers are all new to me but in reading i stumbled across a few things like this

http://www.triumphexperience.com/article/how-to-blow-through-an-su.html

I stand corrected.