Triple SU Carbs and Intake

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I have received today the rebuilt carbs from Tom Bryant, who also set them up to open the throttles at the same time and rate of opening. I will leave them attached to the wooden spacer for now until I get the motor assembled. FWIW the 65 motor was bored 30 over, head cut 10 thou and block decked 90 thou and uses a 74 crank standard on both mains and rods

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I been dying to at least temporarily mounted the SUs to the manifold. I had provided the rebuilder - Tom Bryant - with center to center dimensions between the throttle opening. They came out to 7 inches between each opening which is what the carbs weee set as. They fit the manifold perfectly! Am now waiting on some air cleaners made for these carbs

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@65 Dartman, Nice set up for a /6 :thumbsup: I’ve worked with a few SU’s, I have info on calibrations for different engines and needle profile charts. Let me know if you need some info.
 
Thanks! What do you have for the Jag 3.8 series since they are similar in displacement to the slant 6
E
I sent these carbs to a noted SU gentleman who came highly recommended by slantsixdan. He went through them as well as synchronized them to open all at the same time
 
65 Dartman said:
Thanks! What do you have for the Jag 3.8 series since they are similar in displacement to the slant 6
E
I sent these carbs to a noted SU gentleman who came highly recommended by slantsixdan. He went through them as well as synchronized them to open all at the same time
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I’ll let you know, I’ll dig out the specs. Just bear in mind, a lot of the Jag’s were twin carb not triple. Also a lot were 2’’ SU’s not 1.75’’.
 
I do not. I gave intended usage including specs on the motor to the SU builder up in ME. I can check with him if needed
 
65 Dartman said:
Thanks! What do you have for the Jag 3.8 series since they are similar in displacement to the slant 6
E
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I checked the specs for Jag 3.8. It’s not really apples to apples with your setup. They’re twin 1.75’’ or triple 2’’. - HD6 & HD8.

There’s also two different jet sizes for the HIF6, 0.100’’ & 0.125’’. It’s important to know all this info before selecting a needle. Also, your carbs will have the spring loaded needles, the 3.8Jag’s have fixed needles (HD8 & 6) so I really need to know what you have first.

FWIW, the 3.8’s with triple carbs generally have the ‘UM’ needle (0.125’’ jet ) and twin carbs the ‘TM’ needle (0.100’’ jet).
 
Thanks on posting about the books. I shall ask my SU rebuilder about the jet and needle sizes
 
One important, fundamental thing not to forget with SU’s - 3psi fuel pressure maximum.
 

Don, looks good for sure.
On my Webers same fuel pressure concerns.
I ended up with a Holley Red Fuel Pump and their LOW pressure regulator.
I can send you the numbers if you want them.
You have to look for the LOW pressure regulator.
 
I had a set of matched genuine Italian Webers with the Aussie manifold and I bought a low pressure regulator. I believe I still have it so I’ll try to find it snd see what I have. I think I’d like to run a stock engine mounted fuel pump and the regulator OR a low pressure in-tank pump and the regulator
 
i run a standard slant 6 pump on my hemi 6 with my webers
messed about with a regulator granted it managed the pressure but it also reduced flow to the point where i ran low mid track.

disconnected it and have never looked back. you could run 2 gaskets if the pressure is too high

if you run an electric pump yes i'd think a regulator would be necessary.... as the pump takes no account of rpm



Dave
 
I dug out my regulator- it’s a Quick Fuel 30-804 QFT low pressure regulator adjustable from 1 to 4 PSI
 
A good setup on triples is to run a fuel rail / log. Make the rail a large size (1’’ or more). Inlet on the front, return line on the rear with an orifice to drop the pressure and return to the tank. Three tubes off the rail to supply the carbs.
 
Thanks! I see that’s the super duper chrome plated version. I’ll use what I got!
 
I decided to assemble the SUs to the manifold. My SU builder shipped them to me assembled to each other on a wooden board which made it pretty easy to set them in place on the manifold. Chances are if you happen to have this setup, the carbs will not be connected like mine were. Either way I would do the assembly on the workbench. I can imagine the punishment your back would take leaning over the engine bay and installing each carb.

My carb man set mine up fir the rear carb to operate all 3, which makes it pretty simple to set up the throttle linkage. I have seen linkage set up simikar to triple Webers where each Weber had it’s own linjage from a common rod. Thought of either way to do it?

I have some pancake air cleaners designed for this model SU on order from the a company in the UK. Jn the meantime I ran across these trumpets and decided to buy them as well

One final thought - i know I’ll need to use my adjustable low pressure regulator on these SUs. The builder set these up more or less in a stock configuration with the fuel entering tge frint carb then on to the middle one and then through to the rear one. I need to discuss the current setup with the builder concerning the regulator. I’m wondering if a fuel log feeding each carb might work better, which I’ll get his opinion

After I get the pancake air cleaners, i’ll take some pics then wrap up the assembly and pack it away in storage waiting for the engine.
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with all pipes connected to the pump, makes little difference.. pressure of the liquid in the system should be the same everywhere.
In theory, if set up well, you will only be using more fuel if you have your foot to the floor.
I'd expect better consumption around town.... you will have more torque at lower rpm so that throttle won't be as wide open all the time, less use of accelerator pump type actions, you will run at lower rpm when just driving A to B and make better use of your gears.

Or
you could run a distribution block and 3 lines.
or you could run "two tail" banjos on front and middle and a single on the back one.
or you could set up a return and have the regulator with return line as the last thing in the system before going back to the tank.

each needle valve will have the same "leak" into the bowl of its carb,
pressure in the liquid fuel should be the same at each carb regardless of the pipe configuration.
Its not a big enough "environment" to have proper areas of low and high pressure. The pump does its job, doesn't let it happen.

This style or similar, a bit of hunting will find some for your model
H2 SU Carb Float Chamber DOUBLE Inlet Banjo + Bolt for MG TB Midget 1250 1939-40 | eBay

having said all of that
I run webers off a standard slant 6 pump, 3 carbs in a row, one fuel line with 2 tail banjo on the front 2 with no regulator and have never had an issue. I have not worn grooves into my needle valves, they have not chattered themselves to destruction, and my fuel bowls don't overflow... Although many people told me it would be the case.

lines with proper hose clips and modern auto store EFI fuel pipe. I can see if the pipe deteriorates when its not encased in braid :). I Could have gone all fancy but really no need.

The standard pump self regulates and cares not one tiny bit about the dead headed system.

The OEM chrysler Australia set up for the weber DCOE carbs used a slant 6 pump and the diaphragm, springs and valves out of a 318 pump. presume they did that for volume/delivery stronger spring BUT bigger valves...dunno if that impacts pressure and volume or just volume. i have had no problem with an Australia sourced slant 6 pump

your set up will have similar consumption and needs

Webers are supposed to be at 3-4 PSI

my crappy holley regulator, in pic below (my head was turned by internet chatter on the subject) still in place and disconnected... more trouble than it was worth

a lot of the time the pressure is mentioned because of the prevalence of electric pumps that hammer out way more than 5 PSI all the time, even at idle... then you definitely need a regulator......you are hammering the carbs like you were doing 4000 5000 rpm all the time

i'd personally be hanging onto the cash, aim for a basic set up, less to go wrong, and if it comes to light that you need a regulator, spend when necessary.

OEM use of SU and weber rarely had a return., rarely had a regulator
they either used a mechanical pump or they adjusted the clicking, points based, SU electric low pressure pump to achieve the right volume. its the flow that counts the correct size needle valve and a pump that can keep up for the rpm you engine is turning
needle valves the same size as a 4.2 jaguar might be the key....

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