In my circle of seasoned souls, we always called a carburetor with a sliding piston like the SU & Mikuni to be a variable venturi carburetor. Thanks Chris. Super simple easily understood explanation.
My pleasure :-). What is ingenious about the SU (as opposed to say a Mikuni) is that it automatically 'feeds' what is needed because of the vacuum mechanism. With the Mikuni you can just open the slide wide open and the engine has to try and cope with the unnecessary supply. Not sure if there are any other carb designs that do that ... I feel a googling session coming on!
there we hundreds of bloopers.... I either said it all wrong, or *thought* I said it right until I played it back! Deffo the hardest video I've made so far to get 'right first time'!
Excellent tutorial! The SU system for throttle response is so much simpler than accelerator pumps. So, to know if you have the perfect size carb for the engine you could mount your camera looking in the throat and take it out on the track to see if there's full travel of the slide at fully loaded and sustained rpm/cfm.
It appears that with the brilliant circularly adjustable float bowl system you could drive your beautiful Austin 7 special upside down indefinitely if adjusted properly, notwithstanding Miss Beatrice Shilling's ( I learned her name from kind commenter here last week) modification which allowed momentary inverted or negative G intermittently without stalling out. Nice. I believe that since the slide is indirectly moved by vacuum pressure that it maintains a good mixture even when driving at high altitudes. I live at about 3500 ft. elevation here in Mount Shasta, California, and frequently tour at much higher elevations such as 6700 ft or so and down to near sea level without needing mixture adjustments, just less power at elevation. I love my Skinner's Union carbs. Smarty pants.
What a fabulous explanation, I’ve just fitted an SU HIF44 to our old Harley-Davidson Shovelhead , runs nice , it has a different feel to the previous carb . Thanks very much for a great video.
I just took apart the SUs on a Daimler 2.5 engine I have, this has been a most interesting video explanation of what I was guessing at! Really enjoying you and Brian’s adventures on Oak Swamp too
Thank you, great explanation. I've used an H2 SU for up to 65bhp on supercharged A7 engines, if you are planning an engine with more than 12psi boost and cam/valves that will get you peaking power over 6500revs then go for an H4/HS4.
Thanks Bob - very useful to know! I'm planning to start the build on a NA splash fed motor with big valves and a newman cam quite soon - will prob stick with the H2 on that.
Great Explanation, I've never heard of an H5 or HS5, could these be H/HS4 or 6? I have a feeling the 1" plus 'x' 1/8ths measurement relates to the diameter of the hole (and hence butterfly disc) on the engine facing side? Really enjoy both your video's and Brian's Oak Swamp shenanigans ! Keep up the good work!👍😎
Hmm, I think you could be right about HS5 - well that is embarrassing! Stay tuned as there are more shenanigans with Bryan happening very soon and a new (massive) project will be announced very soon!
The 'number being the number of 8ths' doesn't work for the pre-war HV SU series carbs, only the later carbs. An HV1 is a 1" diameter, a HV2 is 1-1/8 and so on. There is supposedly a HV0 which is 7/8ths but I have never seen one. Around the same era there were also the OM and UBA carbs each being a 1" throat, same as the HV1. They all take the same rebuild kit. My Riley is supposed to have OM carbs but I could only find UBAs (off early Morris). The difference seems to just be where the mounting screws for the dashpot are.
@@thebracketfactory If you order anything from the SU company directly you can add their "SU Reference Catalogue" to your order for free. It's a very handy little book. I add one every time I do an order since their overseas shipping is so expensive I feel I need to get something extra out of them. That book shows exploded views of most of the SUs and has a massive table of what carbs were used in what cars including things like jet sizes, needles and springs used.
Hi thanks for the very informative tutorial.Question,if it’s the engine’s vacuum that raises the piston inside the carb,what happens when you’re cruising along say at 60 mph and you lift off the throttle pedal,to slow down.Would the high vacuum created suck the piston up when you didn’t need more fuel at that moment.Apologies if I’m being really stupid,but I remember the old vacuum wipers going crazy in that situation.
Help I have just bought myself an Austin 7 special and it won’t accelerate? The su carb that’s on it doesn’t have a rod attached to the cap that goes into the slide? Or a spring. Is this correct? Thank you,Andy.
Great explanation of a whole fuel system in the palm of your hand. Two cables and a pipe and your done. You got to love an SU.
brilliantly simple aren't they. I used to be a Weber man but I'm a complete SU convert!
In my circle of seasoned souls, we always called a carburetor with a sliding piston like the SU & Mikuni to be a variable venturi carburetor. Thanks Chris. Super simple easily understood explanation.
My pleasure :-). What is ingenious about the SU (as opposed to say a Mikuni) is that it automatically 'feeds' what is needed because of the vacuum mechanism. With the Mikuni you can just open the slide wide open and the engine has to try and cope with the unnecessary supply. Not sure if there are any other carb designs that do that ... I feel a googling session coming on!
strombergs.... forgot about those!!
Greatly enjoyed on carbs, great bloopers.
there we hundreds of bloopers.... I either said it all wrong, or *thought* I said it right until I played it back! Deffo the hardest video I've made so far to get 'right first time'!
Excellent tutorial! The SU system for throttle response is so much simpler than accelerator pumps. So, to know if you have the perfect size carb for the engine you could mount your camera looking in the throat and take it out on the track to see if there's full travel of the slide at fully loaded and sustained rpm/cfm.
yes, in fact I may try and rig up my go-pro and do that!
It appears that with the brilliant circularly adjustable float bowl system you could drive your beautiful Austin 7 special upside down indefinitely if adjusted properly, notwithstanding Miss Beatrice Shilling's ( I learned her name from kind commenter here last week) modification which allowed momentary inverted or negative G intermittently without stalling out. Nice. I believe that since the slide is indirectly moved by vacuum pressure that it maintains a good mixture even when driving at high altitudes. I live at about 3500 ft. elevation here in Mount Shasta, California, and frequently tour at much higher elevations such as 6700 ft or so and down to near sea level without needing mixture adjustments, just less power at elevation. I love my Skinner's Union carbs. Smarty pants.
Thanks Lance! What car is your SU carb in?!
@@thebracketfactory 1967 MGB-GT, twin HS-4's as stock
@@lanceneuman9528 nice choice!
Excellent explanation
Glad it was helpful!
What a fabulous explanation, I’ve just fitted an SU HIF44 to our old Harley-Davidson Shovelhead , runs nice , it has a different feel to the previous carb . Thanks very much for a great video.
glad you enjoyed it!
I just took apart the SUs on a Daimler 2.5 engine I have, this has been a most interesting video explanation of what I was guessing at! Really enjoying you and Brian’s adventures on Oak Swamp too
Glad you found it useful Leigh.
Great explanation 👍
Thanks!
engine sounds great.
Thanks Nazdagg!
Thank you, great explanation. I've used an H2 SU for up to 65bhp on supercharged A7 engines, if you are planning an engine with more than 12psi boost and cam/valves that will get you peaking power over 6500revs then go for an H4/HS4.
Thanks Bob - very useful to know! I'm planning to start the build on a NA splash fed motor with big valves and a newman cam quite soon - will prob stick with the H2 on that.
Great explanation! Thanks 👍
Thanks! I enjoyed making it!
Lovely explanation. Like the out takes at the end. When can we expect a blooper reel?
A blooper reel could be a feature film!
Great Explanation, I've never heard of an H5 or HS5, could these be H/HS4 or 6? I have a feeling the 1" plus 'x' 1/8ths measurement relates to the diameter of the hole (and hence butterfly disc) on the engine facing side? Really enjoy both your video's and Brian's Oak Swamp shenanigans ! Keep up the good work!👍😎
Hmm, I think you could be right about HS5 - well that is embarrassing! Stay tuned as there are more shenanigans with Bryan happening very soon and a new (massive) project will be announced very soon!
Thanks for this really helpful I have to fit a morris minor carburettor to an Austin seven and was wondering about the fuel bowl height
Glad it was useful !
The 'number being the number of 8ths' doesn't work for the pre-war HV SU series carbs, only the later carbs. An HV1 is a 1" diameter, a HV2 is 1-1/8 and so on. There is supposedly a HV0 which is 7/8ths but I have never seen one. Around the same era there were also the OM and UBA carbs each being a 1" throat, same as the HV1. They all take the same rebuild kit. My Riley is supposed to have OM carbs but I could only find UBAs (off early Morris). The difference seems to just be where the mounting screws for the dashpot are.
ah, thanks for the extra info... still learning about (and collecting!) these carbs!
@@thebracketfactory If you order anything from the SU company directly you can add their "SU Reference Catalogue" to your order for free. It's a very handy little book. I add one every time I do an order since their overseas shipping is so expensive I feel I need to get something extra out of them. That book shows exploded views of most of the SUs and has a massive table of what carbs were used in what cars including things like jet sizes, needles and springs used.
I thought I understood these. I do now!
Recently saw a Ford Pinto engine fitted with an SU carb. nice
Thanks!
Hi have you seen jonathan w video on a lafrance v12 3 years ago All the best Peter
Hi Peter, yes I found that link too... seems there are a handful of like minded fools around the world like me!
Hi thanks for the very informative tutorial.Question,if it’s the engine’s vacuum that raises the piston inside the carb,what happens when you’re cruising along say at 60 mph and you lift off the throttle pedal,to slow down.Would the high vacuum created suck the piston up when you didn’t need more fuel at that moment.Apologies if I’m being really stupid,but I remember the old vacuum wipers going crazy in that situation.
No tickling?
Carb tickling is more of an Amal monobloc thing - SUs can't actually be tickled. Well you could try but you wouldn't get them to laugh....
Help I have just bought myself an Austin 7 special and it won’t accelerate? The su carb that’s on it doesn’t have a rod attached to the cap that goes into the slide? Or a spring. Is this correct? Thank you,Andy.
Hi Andrew - no, that's not right. It should have both spring and a damper rod.