SU carburettors, what you should know before tuning
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- เผยแพร่เมื่อ 11 ก.ค. 2024
- This video is a follow on of the previous video where we captured the carb performance during a test ride. In this video I take you through the SU workings, the adjustment area's and an explanation on what is possible to tune and adjust. We then look at the AFR map/graph of the previous ride and identify what the carburettor must have done. Once all that is done we will rebuild the carb in another video and then tune it in full. That will be the last video
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50yrs in the trade ,I've seen no better easily understood tutorial on the SU carburator than this . Great video again .
Glad you enjoyed it, thank you
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Thanks so much you really help me out!
Excellent teacher. You can really see the difference with a man who shares knowledge compared with somebody who just wants to impress you with how smart he is. Bravo!!!
Thank you
Easily the clearest and most comprehensive explanation of SU carbs I've ever seen! I was an MG, Austin Healey mechanic in the 1960s and early 1970s and I was pleased to see that after I left the business SU dealt with some of the more problematic aspects of their carbs. In the old days centering the jet and then keeping it centered while adjusting the mixture could be aggravating. I was also involved in racing MGAs and MGBs and what we would have done back then to have access to the computer he used to evaluate carb performance! All we really had to go by back then was response to throttle advancement and spark plug deposit color. One classic way one learned they were running too lean when racing was a hole burnt in the top of the piston...clearly a rather expensive diagnostic technique! One thing I wonder about is when I gave up repairing MGs in 1971 I was living in Calif and the air quality standards there caused SU to modify the clearance between the dashpot and the piston. This led to no end of problems in adjusting idle mixture as the slightest amount of residue on either component caused the piston to hang up. Was this a universal problem or just something that happened in Calif? And was it eventually solved?
Thanks for the comments, great write-up... I have not seen that issue over here with the dash/pistons. One thing that did come is was the articulated needle as a result of tighter EC regulations.
The magic of a carburettor has now been dispelled! Amazing patient explanation
Really a mainstay for knowing just what makes my '73 MGB such a wonder and such a joy... Skinner Union / Safety Fast...Thanks so much.
Your a-series videos are hands-down the best explanation series I have encountered. Thank you for taking the time.
I loved the way you explained everything so clearly, getting a spring!!
I just found you this morning on a recommendation from TH-cam and am living uour explanations and delivery. More please
Mate this is the best video I have seen on the SU carburettor and the easiest way to digest the detail required to fully understand how these work and how to diagnose tuning issues 👏
An excellent tutorial on SU carbs and how they work! Thanks, well done.
So well explained that a 38 minute video felt like less than 10! As a fan of Triumph cars and Minis, I always liked the SU. I remember an old timer saying just use engine oil in the damper and don't worry about overfilling it (a little) as it will just run through and burn off. Now I guess that explains why my acceleration curve was not always as I wished. Thank you.
Glad you enjoyed it!Thanks for the comments. Indeed , many state to use engine oil, and overfilling is not an issue. Reality is that this not true... OK it works but not as it should. Its like a blunt knife, versus a sharp knife for cutting.... they both cut , but how and how much force is needed.
One of the best explanations of the SU carb I have seen. Thank you. I look forward to the next one.
Wow, thanks! Thanks for the comments
I have a 1960 Triumph TR3 with twin H6s. These videos have been invaluable as there is not much information out there about SUs. I can’t thank you enough!
Thanks for these SU instructional videos! Very helpful, to put it mildly.
Wow. Thanks for that. Excellent information on the SU
You truly are a blessing to us carb newbies. Thank you
Great video, sorry my first try at the comment misfired. I'd like to share the foillowing.
There are 3 things that I would comment on:
1) for the drop test I plug the holes with a bit of modeling or similar material used to seal drafty windows for the winter. Very moldable and stick stuff.
2) I believe the drop test is done the other way around, hold the piston upward and allow the dome part to drop. There are tables available that list the times for various SU's something like 6 - 8 seconds is normal, as I recall. With my Jab triple carb set-up the objective is to have them all close to equal.. Obviously no adjustment here, only new pars would fix a fast drop time.
3) The spring in your carb is very large in diameter. I have take many different types of SU's apart, including HIF and the spring was always smaller diameter and seated in the very bottom of the chamber..Perhaps SU switched spring types for some reason.
Springs are available, as you probably know, in various strengths denoted by different colours.
BTW the traditional lifting the piston, perhaps only a MM, and observing the effect on engine speed works pretty well for idle richness adjustment
I find the correct amount of oil in the dashpot is such that when you insert the piston/check valve you meet a strong resistance about 6 mm before the thread of the plastic cap engages. Also, these dampers can wear, a strong resistance should be felt when inserting the valve.
On a slightly different SU carb related subject, some HIF carbs and other SU's, such as on the Jag have small ports, covered by thee throttle butterfly plate at idle. This provides a podrted vacuum feed for a distributer designed to use this vacuum source rather than a feed from the intake manifolds.
I have two HIF;s on an MGB engine, one of which I had modified by my distributer tuning expert to provided ported vacuum. Getting the distributer overhauled and advance recurved made a huge performand improvement.
Joe Curto, the most jamous SU guy in the US supplies all possible SU parts and mostly answers the phone and is willing to help with questions.
Again, very well done video, I would not have the patience to do such work..
Very good points that enrich the posting, thank you so much. As for the drop test, i have seen several methods and yours is indeed one of them. I am not sure which one is the better... As for the drop times , its all about the play between the surfaces. And this one in the video is a HIF44 that i picked up from the scrap yard... Once I get the rebuild video done, I will pay additional attention to it. ....
Thank you for this. I have a '79 Datsun with twin SU's and you've answered so many of it's hiccups already!
wow what a great presentation! I wish you lived next door you are a fascinating wealth of knowledge. Thank you so much.
Thank you for the informative video on SU carbs (and all your other projects). I find them educational and enjoyable. I'm currently tuning an SU HV8 carb on my supercharged MG TA special and your video was a good reminder of the variables at work in the process. I look forward to more of your videos!
Great suggestion! more to come ... Love the TA
Thanks for a great video. I worked on cars with these Carburettors when I was an apprentice in the early 70s on British cars in Guyana South America but didn't have to deal with them much in Canada since. I still like to deal with those old cars again as for hobby since I am retiring in Guyana. I will follow more of your videos on older cars
GOD bless
Thanks for sharing
Outstanding explanation and video. Much appreciated, I look forward to the refurbishment. Thanks.
Glad you enjoyed it
Very good video, I have MG 76B and see so many videos, but in this I finally understood how this type of carburetor works, very good explain, help me to tuning my carburetor and mine is different
Awesome video, this has been the best and most clear explanation of these carbs. Subscribed
Awesome, thank you!
As a new subscriber to your channel, id like to say Thank you for your interesting explanations. They are very helpful to a newbie like myself.
Kind regards. 👍
Thank You for this Excellent video. You provided a very comprehensive explanation but delivered in a way that was easy to listen to and has refined my knowledge of SU Carbs.
Glad it was helpful!
Thank you after many years of volvo ownership I am finally beginning to understand the S u carburetor. Many thanks.😅
Information I'll likely never need but I'm glad I have it anyhow. Excellent and interesting presentation as always. Thanks.
Thanks for the comments
So many layers of competance, i like learning from this channel!
Happy to hear that! Thanks for the comments
Great presentation as usual.Stay safe and best wishes from Australia
Thanks, you too!
For the very first time i think i now understand how an SU carb works - Brilliant
I think the SU carburetor design is by far the most efficient and responsive carburetor there is. It’s genius! Where most carbs can only be optimally tuned for a narrow rpm range; Where the SU works amazingly well across the entire rpm range.
Thanks for the comments
The exact explanation of SU carbs I was looking for. Even though I have a HS2 carb I totally can do it with the basic principles from this video.
Glad it was helpful!
Have you heard of a mechanic on you tube called AC Dod, he is a very knowledgable man (a bit like yourself) when it come to SU carbs.
I love watching your videos, to me you explain everything perfectly, my mini isn’t running just great at the moment but with the knowledge I am gaining through your videos I am sure I can fix that.
Thank you for putting up all of your very informative videos, keep up the good work. 👍
Great video, easy to understand,thank you.😊
Fantastic explanation. Thank you, sir.
Excellent detailed videos, thanks for taking the time to explain
Glad it was helpful!
Thank you for such a informative video, it helped me understand more of what I’m dealing with. I’m new to the MGB and have a single SU. Agin, thank you.
Thanks for the comments
Cheers from Brazil !! Your explanation is gold .
Glad you liked it!
Thanks for the video, never understood fully the operating principle of these carbs before.
Happy to help!
Very methodical approach makes it easier to understand ... super!
Glad you think so!
Great job. Didn't know SU carburetors were that easy to understand how it works, comparing with other carburetors. 👍
Glad it was helpful! Thanks for the comments
Great video, very well explained and clear picture!
Glad you enjoyed it!
Outstanding video and presentation. Thank you!
Thank you too!
Really great video !
Excellent video. Thanks for sharing your knowledge.
My pleasure!
I love your carb videos, most informative I’ve seen on TH-cam. I’d love to see an IDA if the chance ever arises.
Maybe one day! Thank you
Thanks for the thorough, well explained tutorial.
Thanks for the comments
Great video, you are a good explainer!
Glad it was helpful!
This is masterclass content! Great video
Glad you think so!
Great video. Very instructive.
Thanks for the comments
Great video, well worth watching!!!
Sorry for the late reply , as i was away for work. But thanks for the comments.
Lovely stuff on to the next vid 👍🏻
Another fantastic video. Thank you
Glad you enjoyed it, Thanks for the comments
Great video , absolutely useful for DYI and not only
Glad it helped
Brilliant information. Cheers
Fantastic video! Although the carbs on my Triumph TR6 are Zenith Stromburgh CD2s I now have a better understanding and confidence to work on then, thank you very much Sir.
Glad it helped!
Very interesting video. I've never knew there's such carburettor design for cars. And the vacuum adjusted piston height blew my mind actually.
As I only deal with oldtimer motorcycles where you adjust the piston with the throttle, and there is no butterfly, but you have idle, choke and needle jets, this is quite interesting... Good vid as always, thaks!
Thank you!
Looking forward to the next one, thank you
Thanks for the comments
A truly masterly tutorial on the excellent SU carburettor, you must have done a lot of recent research into the workings of the SU , as with most things in design, simple is best, and with just one jet and one needle the whole range of mixture is provided for, but only if you do the research as you have! Stay safe, Chris B.
Glad you enjoyed it! and thanks for the comments
Great explanation - thank you
Great series of videos :)
Thanks for the comments, Glad you like them!
Best SU carb video ever! Thank you!
Thanks for the comments and view
Outstanding tutorial on Su's. My life is just a bit easier after watching. On to part two.
Glad it was helpful!
Watching that spring oscillate at the end of the video really reinforced the importance of getting the damper working properly!
Thanks for the comments
Fantastic explained it very well thanks
Top instructor , thank you so much
Thanks for the comments
I learned a lot from this, explaining car technics has your name written all over it.
Thanks for the comments
Super tutorial, thank you.
Yup, now that I know how they work, I have a chance at getting my car to run properly.....Great video....
Sorry for the late reply , as i was away for work. But thanks for the comments.
Very enjoyable Steve and a clear and understandable explanation. I think your diagnosis of not enough / wrong oil type, may be the root of the main issues. Be interesting for you to try that before you also change the spring.
Thanks for the comments, indeed. The spring will most-likely also be wrong for WO. Because the HIF-44 on a 1000CC mini is a bit of an oversize . meaning that the engine does not have enough displacement to create the depression that lifts the piston up to the top under WO. The red spring is 5 ounces , if I am not mistaken.... Will see .
Great video! very informative. thank you.
Glad it was helpful! Thanks for the comments
Loved this tutorial
Your Video was so.Helpfull in my Issues of an XJ6. I underestimated damper oil. Permanent popping and missfiring. Now i made some Experiments with viscosity an there will be efforts. Thx a lot.
Glad it helped
@@D3Sshooter it helfen a lot. I'm experienced with the SU's of the Spitfire and MG. They are not so sensitive for damper oil. So, at first i leave open, to see, if both Dampfer comming up equal. Your Video showed me, why the Jag is missfiring. Dampers came up to fast and mixture got far to rich. Thx again
Thank you for this explanation. I spent $3000 to get my triumph going. I drove it twice. It broke down on the second drive. The car was hunting, losing acceleration and from what you have explained is likely due to what oil is in the damper, possibly a weak spring and it running too lean. Idiot mechanic left me high and dry. Unwilling to fix it. Brilliant explanation on your part.
The mechanic was unwilling to fix it. Sent the car back to me on a truck. Thank goodness we still have people like you.
Subscribed!!!
Amazing channel👍
Thank you so much 👍
Thank you so much, very helpful.
Glad it was helpful!
Fantastic!
I also have an HIF44 that I run on the verge of "much too rich" with a BBC needle and a custom grinded high mechanical lift 268° cam. A series engine tend to give max performances with 12 to 13 AFR under full load, and making them running a tad too rich may prove useful in order to extract maximum performance. One should also try to slim down the butterfly axles and screw, as well a trying on a different set of ram pipes. I tried everything from 20 to 100mm with a custom design in a 3d printer and for my 1330cc engine, 100mm is great for torque around 4000 to 5000rpm, 60mm is great for 6500rpm and over but the best size in my opinion is 75mm for a wider boosted range. David Vizard was spot on, not surprisingly. That's worth from 3 to 6 hp over most of the useful rev range on my engine and a better torque curve.
You can also grind your own needle if you have an accurate AFR gauge, you just need to make sure that your spring and dashpot oil is adequate for you application and then see though the bulkhead cover your needle going through the marks you've made with a pen and slim down where it's too lean. Start with a standard and thick BDL and be careful, you won't be able to add material later !
Thanks for the comments and tips.
Very well done! I have a Stromberg `150 CD but its somewhat similar to SU I was interested at end of your video the spring on the table was sitting there oscillating at its resonant frequency. It sure needs some dampening
Very usefull! Thanks a lot!!
You're welcome!
Beautiful way of explaining the su carb,hope in the future a weber will be on the bench (preferably a 32/36 ;-)
Thanks for the comments, I do have the DCOE weber video's . How they work, calculating and reconditioning. Have a look on my channel under old sporty
or a mikuni phh44
Really amazing, can I send you something to thank you for this amazing video?
Masterclass!
Thanks for the comments
o men, great tutorial, excellent
Glad you liked it!
awesome videos, always super informative! Also, im running twin weber 45s on a counterflow 8valve vw engine where the carb trumpets face the firewall. not ideal and proving a little tricky to tune as i have no space for the flow meter etc to tune that way. Will this gauge help me to tune the twin webbers or is it more for single carb setup? any help or pointers would be appreciated.
Thank you sir
Great video as always.. greetings from Greece... waiting for the next video.....i m interesting on float adjustment....this must be mine problem on my carb because when it is hot hesitates to start because of too petrol on it
Thanks for the comments, I don't expect that to be a float issue, unless your needle valve leaks. That can cause flooding. And off course it could be the float level. However in general changing the needle valve solves those issues.
@@D3Sshooter i m very disappointed with my issue....i have ordered a replacement carb for my engine because the original one had some issues although i have cleaned it ,put new carb kit and had a hesitation in about 2-2,5rpms.soi decided to replace it with s good one (although it is from China) had god acceleration in all rpms no hesitation starts immediately when cold.....but when hot it cranks a lot and finally fires up.....i also order again new one the same China made carb thinking that maybe the 1st Chinese was dead but suddenly thr same symptoms.......i m going to be crazy......i do not know what to do... A mechanic said that thode carbs msy have float problems
Great video and explanations. I have a question, how did you get info to build those graphics
Excellent, I learnt all about these carbs way back and restoring a midget 1500 now, it was a timely reminder for setting up these SU's.
There's a million opinions on this, but I did send the carbs off for a sonic clean. After the process, I found it almost impossible to balance the carbs once they came back. Coincidence? I don't know, but maybe I would take a different approach next time around.
That is strange, of course the ultrasonic cleaning should be with all parts disassembled... and put back together on the same carb. Else you might have issues..
Great explanation.
I have twin SUs and I find it hard to perfectly tune them.
I have changed the dampers as they where not the same. And I have mated the pistons to the Chambers so they move the same speed.
And basically rebuilt everything. New needles, jets and everything. But I just realised. I never replaced the springs.
Volvo?
@@IngeBall yes.
Glad it helped, Thanks for the comments. Twin's are not that easy to tune as they need to match....not only in needle-jet setting at idle, piston drop and rate, damper and linkage. besides the fact that cylinders might be a bit different in suction( engine that is).
Thanks for the comments, the same SU's were used on Volvo
When I was a young bloke with more money than sense I mucked around with SU. Carbeurettors. These was an array of different size jets available and about 5 million different needles. Apart from the different springs available the viscosity of the oil I the dashpot affected the air / fuel ratio. I thought I knew more that the engineers who designed the car. I no longer hold such youthfully enthusiastic opinions
Stavros
Thanks for the comments
Great
Wish I'd known 1/10th of this when I was fiddling with British cars half a lifetime ago
Thanks for the comments
This is interesting, but I subscribed for Old Rusty videos.
Thanks for the comments, I know Dave , and so did many.... OLd Rusty is not forgotten and will be back.... I do many things
Fantastic,God Bless,how much oil do we now to put in,and I have seen one video use trans fluid for the oil ??
Hi this is a great video. Thanks. I assume that with the oil the dampers it should drop at a much slower but even pace? Should the cylinder be 1) somewhat resistant or 2) very resistant or 3) difficult to push up by hand with oil in the damper? how does one know if the oil is too thick/heavy? Thank You for your help
I’ve found ATF fluid to be the most responsive in my stock 240z. ATF viscosity is about SAE 15. I just use the same stuff I use in my boat: Amsoil Torque Drive.
Thanks for the comments , great tip
Very informative videos; you take a technical subject and make it very interesting and understandable. I have a 1968 Volvo wagon with a B18 engine that has a fuel injection cylinder head and I 'm using the original SU Carburetor's.
I know that no one can diagnose a problem over the internet but one concern that I have is I have this car for 5 years and I just can't seem to get the engine running with out having the spark plugs fouling up. I've tried to lean the carbs out so it will still run and I take it out for the " Italian tune up"...that's drive the crap out of it and when the engine cools down I remove the plugs and the are very black with carbon deposits.
MY BIGGIST WORRY IS I HAVE BEEN TOLD THAT RUNNING AN ENGINE IN THIS MANNER CAN REMOVE THE OIL FROM THE CYLINDER WALLS AND RUIN MY ENGINE...IS THIS TRUE AND AND SUGGESTINS WOULD BE APPRECIATED/THANKS IN ADVANCE.
Thank you for the comments
always remember setting cars co to 3-3.5 as per spec,always ran like pics with su carbs,always found it needed to be 4- 4.5 min although an mot limit of 3.5 at the time,always found the needles and main jets wore in no time,i prefer a webber!