How to Tune SU Carburettors

[@boatman222345]

Great video on the basics of working on SU Carbs. I worked as an MG, Austin Healey mechanic in the 1960s and early 70s and although the SU Carbs used in them are similar to the ones on this Jag there are some slight differences in design. To adjust the jets for rich/lean mixture on MGs you use a wrench to move the jet up or down by changing the height of the seat. They used to sell a special tool for this but I always just cut most of the handle off a suitably sized open end wrench which gives you a stubby sized wrench which is much easier to use underneath the carbs. For synchronizing the carbs I just removed the air filters and held the end of a small rubber hose on the edge of the carb throat and placed the other end in my ear. The sound of different air velocities is quite distinctive and with a little care very precise adjustments can me made with this method. One point not made in this video is that it is absolutely key to do a thorough job of cleaning the inside of the dashpots as well as the skirt of the piston that runs up and down inside it. Many times varnish that collects on these surfaces can cause the piston to hang up, or lag behind in responding to throttle changes. As mentioned in this video these pistons and dashpots are a matched set. The reason for this is that fairly tight tolerances are required for them to work properly. Unfortunately this eventually became a problem with MGs (at least in Calif) as EPA requirements forced MG to tighten up these already tight clearances. I owned a small sports car repair shop in Calif in the early 70s and MGs sold in Calif at that time were very difficult to set idle speed on as the dashpot pistons were constantly hanging up. It would have been illegal to hone out the dashpot chambers a tiny bit but doing so may well have solved this problem.

[@nalmeb]

Hi Boatman as you have some experience with the MGA which I also own , maybe you could make a video.

[@lee2513]

You so much for posting this!! Unbelievable, because I've never seen this until yesterday. I was 17 yo and I was there! That is a 17 yo me standing near James Browns' getaway limo out in front of the auditoriym after the ceremony!! An unbelievable day!!

[@alanpennykid133]

Thanks for the video. I'm refamiliarising myself with tuning multiple SUs after buying a Rover 3500 P6. I've had many cars with twin SUs over the years. It's been a few years now though since the last one (Jag 3.4S) and I've never had HIFs before so that's new. When I bought the car it was running and driving nicely but obviously running rich as it smelt fuelly and also started without choke no matter what the temp was. Running very sweet now though and starting easy too(with choke when needed).

[@frankpowell1778]

Hi Adam, your video is the first to pop up on my search for SU carb adjustment!

[@guyledouche2569]

Thanks for the video. It has been a great reference for me to keep my customers 240z running as it should. Hadn't touched a set of su's since the 80's, now in the past 3 years I've had 2 customers show up with 71 240z's both with carb issues that the local z specialist would not touch. Thanks to your video I can tune them peffectly.

[@relmdrifter]

Thanks for the video. Tuned a set by ear. Buying a tool for air flow to fine tune them. Also learned how to properly use the dashpot lifter, thanks again.

[@dornosaur5746]

Thanks mate! I have a datsun 240z. I found out my su carb was completely unresponsive to the mixture screw. I took it to a professional tuning shop and the took the bell housing off and unstuck something. I wish I had asked them exactly what they did, but if you find the min and max of the mixture adjustment makes no difference, that could be your problem too. The weather in Seattle is starting to get a bit colder so I'm expecting to try again in the next few weeks. Thanks for your video, I think it's a great summary and plan to follow it next time.

[@FabienProxTrm]

Restoring my 240z and I have 2 SU carbs!! Your videos will help a lot! Cheers man and happy new year :)

[@ajay-xjs]

The 240Z is a stunning car 👍 I never realized they had SU carbs, proves they are good as Datsun rarely got anything wrong.

[@chrisscott9996]

I'm glad I found this. I'm installing the engine in my '66 Austin Healey Sprite.

[@LivingWithAClassic]

Hope that tuning goes well!

[@doddsy799]

my 66 sprite brought me here aswell :)

[@junglejoose813]

These videos are completely enlightening and motivating. Going to refurb some roundtops now to replace the flat tops in my 510. Thanks!

[@tonycollingridge4347]

Hi Adam, another great video. Thank you. There are so many different schools of thought on tuning SUs and I definitely think it is an art rather than a science! Everything you did on the XJ mirrors what I do on my Mark 2 except that I think you suggested that you should undo the throttle linkage before tuning and tune the two carbs completely separately before re-connecting the linkage. My manual (Jaguar and several others including Haynes) is/are clear that the linkage should be loosened at the beginning to ensure that the butterflies can be and are both completely closed and then re-tighten before going on with the rest of the tune up. I've always followed that practice and it works well for me. Interested to hear your thoughts on that......

[@michaelbahe5370]

It is great to see how the Unisyn actually works. My car is a Jaguar E-Type V-12 (73) - so it's 2 sides to tune (4 SU's) which is (I think) balance each side and then balance the 2 sides. Thanks again!

[@karljay7473]

I've got a Toyota 8RB it has the dual Asian carbs, they have the only vacuum activated power valves I've seen in a domed SU type carb. Toyota made a few performance engines back in the day and the 8RB is a 2L single over head cam 8 valve closed chamber iron head on the same block as the 18R and 18RG. I noticed the SU carbs pull very strong, it's like a nice flat torque curve and that makes them fun in the hills.

[@byteme9718]

I'm not sure if you have an earlier video but the first step is to make the main jets are serviceable and set to the correct initial heights and that the throttle spindles have no lift. If any of those three are not right it's a waste of time carrying on. Jet heights have often been messed around with by owners in the past. You also miss an essential step while tuning and that's to clear the inlet manifold of excess fuel regularly. This was a standard procedure and every few minutes entailed raising the RPM to at least 2000 RPM and holding it there for 30 seconds. Then you can use the lifting pins and make adjustments however the lifting pin method works well on some engine and less so on others so the best method is to check spark plug colour after a run.On this age of car the lifting pins were never intended to be used. They were just a hangover from earlier times. You also seem to raising the RPM intermittently using the cable quadrant however you still have the two carbs disconnected to reset air flow.

[@jonwills286]

You know your stuff

[@roy-whereamI]

It's hard to judge how much to raise the piston with the lifting pin. You say slightly. Does this mean the smallest amount of movement I can make? If there's no change in engine speed, does it mean I didn't move the piston enough? The problem is that, no matter what the mixture is, the engine will always stumble if you raise the piston a little more than "slightly" right?

[@connorharrington617]

Useful! I have twin SU carbs on my 1961 MG

[@Plodalong-allday]

Thanks for such an informative video Adam. I’m learning to tune my Series 1 E-types triple HD8’s.

[@dansdoves3650]

Thank you for the tip about only tuning the carbs one at a time . I'm having a little trouble getting them dialed in as good as I like but if I watch enough how to's about them I should be able to figure it out. Most of my friends bad rap SU carbs and tell me I should change over to a Weber carberator. They put SU carbs on so many different cars and usually sport type cars that I figure there must be a reason and they can't be that bad or the carmakers would have used something else. I have a 62 Volvo 544 Sport with a B18 engine in it.

[@LivingWithAClassic]

They are good carbs and really good for street use. One other thing you can do if you get confused is to set the mixture the same on both carbs by measuring the height of the jet and make sure they are the same. Then if you make the same mixture adjustment to both, you should get pretty close to start with

[@madeintheusa2203]

The number 1 issue with old SUs are throttle shafts that leak air. Spray carb cleaner around both sides of the throttle shafts in each carb and if the idle changes you need to replace the shaft bearings.

[@AthelstanEngland]

Thanks very useful recap. The graphs made it easier to remember too.

[@EcBuddy123]

Getting my hands on a 71 xj6 this Friday so this is going to be helpful, as most of your other videos! I'm extremely excited!

[@MrSimonkd]

Many thanks, very clear except one thing that is puzzling me. If you loosen the throttle linkage how does it still rev when you manually rev the engine? Thanks

[@stephentempleton9208]

Super helpful for tuning my XK120- thank you!

[@LivingWithAClassic]

Glad it helped!

[@1qazandrew333]

Thank you for a truly excellent video! HUGE help for my twin SU carb mini!

[@phabel59]

Really helpful, off to reset my 61 mark 2 Jaguar 3.4. Thanks

[@mike130557]

I will be tackling an MG Midget tomorrow, as she is running really badly. OK when warming up, but as soon as she reaches normal temperature, she backfires, runs really rough and conks out! Fingers crossed for a good result! Any hints and tips, gratefully encouraged and accepted!

[@classic1989mini]

Wow, very impressed with your work, Will try it on my mini!

[@rhyshanrahan8621]

Hey mate I have a 1974 triumph 2500tc manual really needed this video thank you

[@andrewfreeborn]

Really useful video! Thank you Adam. I've got a 1976 Mini GTS, which is a South African model that came with twin SUs.

[@henryportwood9364]

I’m changing from the stock airbox on my 65’ mini (twin HS2’s) to k&n cone filters. Will the air/fuel ratio be the only adjustment needed?

[@terrytitus8601]

59 544 Volvo..at the point where I must try to get it running to further adjust timing and carbs..been a struggle.. videos aid a great deal..have added electric fuel pump.. will struggle on

[@quentenpollard6209]

Dear Adam spot on video.

[@zenoclarke5029]

Hello love your content, could do with some help. I'm trying to to set carbs on series 1 jaguar 4.2 with the 3 su set up but every time I'm trying to balance it's dipping the engine to much. Someone suggested turning idle/tick over up but apparently you don't do this while setting these up. Can you help please ?

[@theoriginaljc-j]

Very impressive and clear instructions. I am now looking forward to getting stuck into tuning up my carbs - 👍

[@thelearninghub716]

Hi Adam, can you do a video on how to take the rear calipers out and reseal them on a Daimler Sovereign 1978 xj6. Would really appreciate it as your videos are really helpful.

[@emilegoguely4032]

Thanks Adam, that was perfect, tunning my 88 mini tomorrow

[@LivingWithAClassic]

Good luck with your Mini! Hope you get it running sweetly

[@DuskersHusky]

thanks for your video, i have been having a nightmare with my dolomite, im going to give this a try tomorrow cheers!

[@ajay-xjs]

I wish I had the internet 30 years ago 🤣

[@marinelifer1752]

I am from "Rolls-Royce technical forum" on FB. Brilliant videos!

[@LivingWithAClassic]

Thank you! I love that forum and read it a lot. Hope to own a Rolls-Royce some day 🙂

[@byteme9718]

This doesn't work on a V8 Rolls-Royce. You can mess around with the mixture screws and they make no difference.

[@yvesb7171]

Hi Adam, many people does have SU carburettors on their MG Midget or MG B. Would you make kind of the same video for theses HS2 or HS4 carburettors ?

[@mikesilsby1649]

That was actually very helpful

[@jwh475ezc]

You should emphasize the importance of the throttle plates (butterflies) closing completely at idle. You did mention the throttle stops but if they are not in the correct position on the linkage the plates could then be slightly open. Also a timing light is useful for reading rpms while making adjustments

[@cyrielgaemers]

Thanks!

[@cyrielgaemers]

I've send you an Instagram DM!

[@andreader6826]

Great Adam, excellent Video!

[@LivingWithAClassic]

Thank you Andre! I'm excited to launch it 😊

[@michaellancaster8583]

Love from New Zealand. Looking to put some on an L18 in a Datsun 720.

[@neilevenden2336]

very helpful for my Australian MGB

[@LivingWithAClassic]

Thanks for watching!

[@louiegaring6389]

thank you mate, this is very insightful!

[@joeclayton4434]

I have a 3.5 sd1 v8 efi converted back to carb, when i accelerate at 50 55mph it bogs would this be some thing to do with the su carbs its running bbw needles

[@biodread10]

I have a 1978 Triumph Spitfire with dual SU HS4 carburetors.

[@ianross2090]

Hi Adam, love your videos. I have a 420 Jag with very unhappy fuel issues. The main issue is the SU's (2) need refurbishing/tuning and your information is very helpful. The car also has an electric choke. Will you be doing a video on the auto/electric choke maintenance and tuning etc?

[@zenoclarke5029]

Thank you for sharing and nice work. I'm attempting a series 1, e type, 4.2 tomorrow. Thank you 👌👍

[@tjmthejagmandownunder]

Thanks Adam! Luv your spark plug blanking plugs!

[@LivingWithAClassic]

Thank you! Haha they add horse power

[@timcherrett3890]

Thanks for this! Am about to start rebuilding a pair of HS6 from a Volvo Amazon

[@LivingWithAClassic]

Good luck!

[@timcherrett3890]

@@LivingWithAClassic really appreciate your clear instructions and advice. I fear I may have to replace spindle bushings on mine 😭😭

[@dannymartinez8314]

So i inherited my adopted father's custom built chopper shovelhead engine with a beautiful BIG S.U. carburetor, it's almost impossible to apply the rear foot pedal on forward controls ( foot pegs) because the air filter housing is almost sitting on the shin of your leg and start pressing your shin into it as you press the brake, I remember asking how he used the only brake with the carburetor, he told me that he would have his foot on the edge of the foot pedal with his toe pointing inward so his big toe could reach the brake pedal, scariest shit i ever heard, so both ways was asking for a injury ending the joy of riding a motorcycle, so this S.U almost lost it place on my chopper because i knew nothing and could not figure out any useful info on it, until i found these videos on living with a classic, and now i act like i am the expert on these carburetor, because they are simple and don't struggle with starting or messing with a choke, this S.O.B doesn't have one, IT DOESN'T NEED NO 🙀 CHOKE, facts, it's doesn't even need you....ok that not true, my point is, when i jump on to take.a ride and open the petcock and i see the glass fuel filter fill up and fire it up, i hear Bob Marley singing “ Don't worry, be happy", as i ride on down the road, and i fixed the brake problem by putting a extension spacer on the brake pedal, and now my whole foot is on the pedal and my leg feels comfortable on the outside of the carburetor rather then having it right under it.

[@andreaspersson2021]

Hello! I have a Volvo 245 with a single SU hif6. I have been trying to tune the carb according to your video. When lifting the piston the rpm drops which should mean that it runs lean. Now I have screwed in the jet adjusting screw all the way and it still runs lean. Is this normal and what should I do?

[@robp9124]

Firstly , great vidoes :) . Have you tried the STE Syncrometer ? , I love it .I have a Uni-Sync , but was never really happy with it's accuracy. Just interested in your thoughts. FWIW , I'm working with twin HS6's , on a Datsun 260z.

[@johndavey72]

Hi Adam. I thought l was subscribed , oh well old age kicking in ! Hadn't seen you for a while and just checking everything is ok with you and the family.

[@fentuz]

I have a frogeye sprite with a 998cc flat top and big valve ported head with 1.27 rocker (rather than 1.22). How do you selected the correct needle size for the twin su hs2? Thanks

[@aguiloco23]

I learned a lot, thank you very much!

[@fabiopapa2819]

Is the screw you touch with the screwdriver each time the idle adjustment screw?

[@davidlis6709]

Excellent presentation and explaination. I make car videos myself

[@freestyla101]

What is fast idle? Is it just a limit of how much the choke can open?

[@alellish9167]

Just saw this video,how do you tell if the needles are correct? I have a 544 with a b20 engine,I think the po used it for racing,and has changed the needles from stock.

[@philgen4818]

Hi Adam, I follow your channel and subscribed to it already. On my recently purchased Jaguar MKII I think I have an issue with my HD6 carb's. The front one is spitting fuel from the floater bowl into the ventury when the fuelpump is filling the bowl. This with a non running engine. With the fuelpump off I have the same effect by pushing slightly with a screwdriver on the jet inside the body of the carb. Can this point out to a damaged diafragm? I see no other reason why the fuel is entering the ventury. Do you see an other reason? Can you explain the function of this diafragm? Thanks in advance for your answer. Phil

[@deniscortes9200]

MAN! THAT WAS GOOD. THANKS.

[@LivingWithAClassic]

I’m glad you liked it!

[@philippemilliet8129]

Perfect. I will tune my mga twin cam

[@bobstride6838]

Hi Adam, could you please discuss kickdown on the XJ6 series 2? I have a problem with my 1974 when it gets to a hill it kicks down a gear but immediately goes back up a gear and then it keeps going up and down continuously. If I manually put it second gear all is fine. Where should I start to look for a solution? Your help would be much appreciated.

[@LivingWithAClassic]

I can try and cover it pretty soon. I may need to adjust mine too

[@pastorraudel1261]

Such a great video!

[@tryphonpantazopoulos2676]

can you please tell me where to purchase this syncroniser tool?

[@cyrussataravalla6731]

Ma786sai dua how can I balance and tune both SU carbs on my 1982 Rolls-Royce Spirit

[@edhaskell1554]

Are you going to show what turning that mixture screw really does? On my MG TD it you turn a bolt on the bottom of carb to raise/lower the needle in the jet. Does a Jag work the same way?

[@LivingWithAClassic]

Every SU carb is a little different. On these the screw pushes a rod that raises or lowers the jet. In my video explaining how the SU works I go over this

[@paulwisdom5383]

Hi Adam how much oil should the dash pot have? I'm very new to carburettors!

[@LivingWithAClassic]

It’s very little, just up to the top of the type that the dampener goes in

[@gunnarMyTube]

Very clear, thanks !

[@LivingWithAClassic]

Thanks for watching 😊

[@victormadrigal931]

I have similar Hitachi carbs on a 69 roadster fair lady but having tons of problems were can I get sone parts can you give me any links or pointers were to go I em in San Diego ca

[@55mena]

Why mi jaguar mk2 1967 3.4 ..has fuel leak bottom plenum (thru the zirk )

[@sente27]

got myself an mazda rx7 fb with an elford turbo kit. it also has an Single SU carb, so this is going to be a really good help. ;)

[@tpantazopoulos]

How do you loosen the throttle linkage?

[@flemmingranch8777]

A very good and informative video …..

[@LivingWithAClassic]

Thank you!

[@kennethtalbott2233]

great info thanks.

[@harrimacslive1187]

Didn't see you reconnecting the throttle linkage!

[@CauliflowerMcPugg]

Great video👍

[@LivingWithAClassic]

Thank you!

[@hrdcorebeast]

I have a pair of these that need torn apart and checked out due to the car sitting for years and having bad fuel in it. I put a new fuel tank on it and inline filter and now i'm ready to do the carbs since when we ran it last year for the first time in a long time we discovered leaks at the bottom of where the jet goes up through. I'm working on a '53 MG TD with twin H2 SU carbs. This is my first rodeo with car carbs let alone a strange set up like this so unfortunately I don't know any old timers to give me a hand since it's not american. I'm hoping i can just take them apart and clean them and put new seals in and everything will be ok, however i'm not sure if it was set correctly to begin with. It has a manual choke so what do i need to do for the fast idle adjustment? And do i absolutely need one of those tools and where do i buy such a gadget? I read somewhere you can sort of balance them by ear by using a piece of hose to listen to the air going through each one. Thanks for the informative videos.

[@craigmorton1944]

Hi My first car was an MG TD --- I have always used a 3 foot long (say ? about 90 cm length) piece of garden hose to set the balance on the carby air intake. You are listening for the same amount of "sucking" sound. When the two are equal then your ready to go. The only thing is to make VERY sure that you are holding the end of the hose at exactly the same spot on each carby. The "ear" end of the hose you hold the pipe pointing up and right next to and just touching your ear lobe for best sound. I can easily balance three carbys on a jag E type--- no hassles with my garden hose. Just keep going back and forth between the carbys until each sound is balanced. deeper sound is too lesser suck--- higher pitches is too much suck--- just balance the tone. The idle will rise or fall as you adjust the carbys when you have both OK readjust the idle to a good engine idle rev. Dont forget to isolate the throttlelinkages before you start and reconnect when finished. Final check with the garden hose again and your ready to go. I have had 19 British sports cars in my life time and thats how its done-- by the way I am a grey haired old bloke with lots of sports car experience. Best Wishes craig

[@hrdcorebeast]

@@craigmorton1944 Thank you! My only other question is how in the world do you adjust the mixture on these? I don't see a mixture screw? And there are no springs behind the pistons...one blog i read said the MG td carbs didn't have a return spring for the pistons because they were heavier and used their weight to return. Is this true? Thanks.

[@craigmorton1944]

@@hrdcorebeast Hi One of my manuals specifies "Blue springs" (2010 SU manual) but my 1950s TD and TF workshop manual doesnt show any springs? I cant remember my car because it was 50 years ago ! Your carbys are H4 type so look up H type carbys at sucarb.co.uk/h-type-carburetters All H type carbys are the same so you can get lots of info there. The richen and weaken brass nut is at the base of the carby around the jet . see sucarb.co.uk/technical-h-type-carburetter-diagram By the way dont forget to fill the dash pots with engine oil before tuning begins . Dont be tempted to use ATF (auto transmission fluid) or some other light or heavy oil .Engine oil is fine and specified in both of my workshop manuals 2010 and 1950s. Tighten this nut UP for weaker and loosen it DOWN for richer. Small turns are only required start with two or 3 flats on the nut to start then fine adjust from there. If your tuning from scratch follow the instructions in the su carby site above. Also Look at Moss Motors . They have heaps of MG bits for sure. www.moss-europe.co.uk/ This is the UK site but they are in Europe and the USA with sub agents in Australia. ( probably also elsewhere) What country are you situated ? I am in Sydney Australia. Google your MG car club in your area. The would welcome you and your car for sure. Best wishes and let me know how you go craig

[@hrdcorebeast]

@@craigmorton1944 Thank you very much! I have already been to moss and that is where i got my carb rebuild kit from. I'm from the good ole USA. It's not my car, I'm working on it for a guy i know. Car was very neglected for years so we are trying to get her back to life. I just had to put a new fuel tank on it for him because it sat and water rotted out the bottom of the tank and apparently the seals for the jets dried up because we had it fired up but it pissed out the bottom of each carb so we quick shut it off and now here i am. I have emailed moss about these tech questions but have yet to receive reply. It looks like they are behind right now due to the so called plague, but I'd rather hear from an old timer like you any way. I'm 31 now and I feel i know a lot more about cars and fixing things than most my age because I've always listened to the old guys when everyone else would ignore them. My wife says I'm a grumpy old man at heart.

[@craigmorton1944]

@@hrdcorebeast Hi again You will for sure get the TD all together with some sweat and persistance . Thanks for listening to an old bloke. I currently have a MGB 1969 and an E type Jaguar roadster /convertible 4.2 litre also 1969 model . I sold my Aston Martin DB6 to buy the E type. Sincerest Best wishes to you and good luck with the TD craig

[@simontogo]

How was it after the test drive, Adam? Did you need to fine-tune it?

[@LivingWithAClassic]

I did fine tune it a bit after the test drive. Made both a tiny bit richer. I will check it once more after a long drive on the highway after its inspected. I've booked a time on Thursday for that

[@simontogo]

@@LivingWithAClassic Awesome, Break a leg!

[@duncanwilson9020]

I have a 1970 mgb GT running twin HS4's

[@pastorraudel1261]

Why is it again that leaner makes the rpms go up?

[@tabspike]

I have a 1969 Triumph Spitfire Mk3 I hope to tune.

[@LivingWithAClassic]

Lovely car! I hope to have a spitfire someday too. Good luck!

[@mckav2358]

Very very interesting

[@richardlacombe1736]

Why is it.. that you are not aware that when your blipping the throttle, your only blipping one carb, not both.. You should be blipping the carb that you are adjusting..

[@aldomorberg1784]

Nice tool

[@ashberkley]

What is the job of a carburettor?

[@LivingWithAClassic]

It delivers fuel to the engine on older cars that don't have fuel injection

[@ashberkley]

Hey! I have a question for you... I have a factory manual xjs. I think I had to replace the gear linkage bushes.... Any advice please???

[@rovercoupe7104]

Sixty Sprite. M.

[@jeffreyprice773]

That AED was a pain. Unreliable. Hope you don't get a blowback with the air cleaner off, fire. Tip> listen to the exhaust note.

[@55mena]

Hello