• Hi Guest! Being a Paying Supporter is NOT a requirement to participate at BCF. However, subscribing will help ensure we can continue to serve the LBC community for years to come. If you enjoy BCF and find our forum a useful resource...Please consider supporting us by **Upgrading**
    (PS: Subscribers don't see this banner)

Having fun with my SU H6's Basic Question


Darth Vader
Been a long time since I did anything with a pair of SU's so I have some basic questions:
1. When the car is at rest, are the butterfly valves supposed to be closed or open?
2. If they are open then pulling the choke will close them partially to allow the car to start?
3. Once the car is running the butterfly's are in what position?
As I read this I'm getting more and more confused,The SU manual did not help me on this basic stuff, so I need some help!

Thanks, Tinkerman


Jedi Warrior
On H6s the butterflies should be open a tiny amount to allow tickover, when you pull the choke out it lowers the main jets by about 3/16-1/4" and opens th butterflies a tiny bit more.

Lowering the main jets makes the mixture rich, ie more petrol for a given amount of air.

The dashpots should be right down to start and they get lifted by vacuum in the inlet manifold as engine revs increase. As you press the accelerator pedal so the butterflies open more and increase the vacuum in the manifold, which pulls up the dashpots and the needles out of the jet increasing petrol flow to match air flow. Clever stuff and SU stands for Skinner Union because the originals had leather bellows.

I hope this makes sense.



Jedi Knight
Country flag
We are all awaiting for the start up Dick!!


Jedi Warrior
The important settings on H6s are:

1. Take lids off float chambers invert them and a 7/16" drill shank should just slide under forks.

2. Make sure floats don't have fuel in them.

3. Set main jets 35-38 thou down from jet bridge. Shoulder of needles should be flush with face of Dashpot.

4. Make sure with tickover screws backed off that butterflies are carefully matched by sliding a 1.5 thou feel gauge under each of them. The same effort should be required to pull it out from under either.

5. Make sure when you attach the choke linkage that the main jets are still 35-38 thou down.

This is how they were set by the factory and the cars ran perfectly once tickover speed was adjusted. Nothing else was needed.



Country flag
"Skinner"..I thought that was a family name. Of course back olden times England that doesn't rule out the family being in the slaughter house or tanning business


Jedi Warrior
poolboy said:
"Skinner"..I thought that was a family name. Of course back olden times England that doesn't rule out the family being in the slaughter house or tanning business

I believe they were.

Similar threads
Thread starter Title Forum Replies Date
5 TR2/3/3A Macy's Garage restoration done and having fun Triumph 6
J TR2/3/3A Having fun installing the front bumper and bumperetes Triumph 7
L Having fun with Photoshop Spridgets 21
LastDeadLast Having fun with a video camera Triumph 7
Tinkerman Tractor engine assembly - BOY am I having fun! Triumph 7
Mark_Gibson Making Progress, Having Fun! [TR-2 Dismantling] Triumph 10
G Process of elimination.....are we having fun yet? Triumph 11
S TR2/3/3A Delrin bushing and I am having a problem Triumph 13
Michael Oritt Having a problem here.... Austin Healey 9
M TR4/4A Having problem uploading pics...no go...why? Triumph 3
TR3TR6 TR2/3/3A Anybody else having a bad day! Triumph 31
Lukens TR2/3/3A Let's see if I'm still having the 'Britishcar forum not responding" problem Triumph 3
T TR2/3/3A having no shame I ask another question about a TR3 engine that is giving me fits Triumph 10
J Having trouble getting Forum to work on IE 9 since it was switched to the new format. FORUM Help 7
RickB OT - Peter having State FLL competition today Spridgets 9
MY66AH Having Master Cylinder Troubles Austin Healey 5
bgbassplyr I'm having a problem with.... Triumph 17
M Having a hard time removing the rear bumper [pic] Triumph 4
T Having clutch issues? Triumph 7
Tinkerman I Having A bad vacuum advance line day Triumph 5
RickB friend with lbc having engine troubles Spridgets 8
L I'm having problems with my timing gears Spridgets 19
bighealeysource Having trouble getting a good ground on my BN6 Austin Healey 5
T Still having issues with the electrical MG 5
RickB Anyone else having a White Christmas?? Spridgets 21
Got_All_4 Having Problems? Try This. Triumph 0
regularman The bad thing about having a high rear gear Spridgets 13
jlaird Having an awful time Spridgets 12
S I'm having ignition problems too Spridgets 19
danielnorton Still Having exhaust trouble Spridgets 13
LeeMcKee Having my Head Shaved Spridgets 20
W Having to pump pedal for pressure Triumph 4
J so i'm kinda having second thoughts about my car.. Austin Healey 29
Randy Harris Having made the fateful decision.. Jaguar 0
Hamish Racing TR2/3/3A TR3a track fun in uk Triumph 2
skystryd remind me it's fun. good idle. rough when accelerating Spridgets 6
jlaird MGB Tomorrows fun MG 8
JPSmit OK not British but a lot of fun here Other Cars 1
Jim_Gruber A Fun 97th Birthday Party Spridgets 4
C TR6 More fun with Lucas Triumph 5
NutmegCT Disc brake fun Other Cars 33
G TR4/4A And the fun continues...rear main leak Triumph 5
NutmegCT T-Series SU fuel pump fun MG 20
Jim_Gruber What a fun evening with Bugsy IV Spridgets 3
Jim_Gruber Bugsy was out for his first real romp today! And it was fun!!!! Spridgets 3
HealeyRick Car Alarm Fun. Spridgets 4
Joe Reed MGB Wiring problem....this should be fun :[ MG 4
Tinkerman TR2/3/3A Rear Wing installation fun................... Triumph 3
HealeyRick Fun at the NY Auto Show Spridgets 5
Gray_Cat This Could Be Fun For Someone! BE in Carlsbad CA Spridgets 2

Similar threads