SU Carb Tuning - Part 3 and More Finishing Touches | Roundtail Restoration

If you are interested in more pictures of the restoration and detailed write-ups of what I'm doing, please visit my website www.roundtailre...
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Want to see other random technical videos, not exclusive to my Spitfire (like generator testing)? • Technical Videos

[@mike130557]

Thanks, Chris, for spending all your time putting these Carb videos together. I’m having major ‘issues’ with the same setup on my wifes’ MG Midget 1275cc, 1973 vintage!!! These SU Carbs are so tricky to get tuned and balanced! Unlike your Triumph, there is very little wiggle room around the bottom of them, the damn wheel arch gets in the way!!!

[@roundtailrestoration]

Glad you liked them. Definitely learning as I go. Once I got that RPM response after lifting the piston, it started to come together for me. Yes, the Spitfire is very roomy and easy to work on!

[@NialPowerCork]

Great video Chris, always very clear and logical I enjoy your way of working. I’ve just overhauled a set of SUs and am going to start with this method to get the basics right.

[@roundtailrestoration]

Thank you. SUs are pretty basic, but it does take some finesse to set them up, I think. I still struggle to get it right, but I think I'm slowly picking up on it. Setting the jet mixture is where the black art is, I think.

[@NialPowerCork]

@@roundtailrestoration yeah the tolerances are quite tight. I put new bushings and spindles in and did a full overhaul, boy I had some trouble getting the jet centred on one of the carbs, had to take it off and do it on the bench in the finish but fluked it correct in the end, now the piston position on each looks very even at tickover and I can get a stable tick over anywhere from 500 to 1000 rpm. Haven’t tried a flow meter on them yet but I think it’s going to be OK, without specialist tools getting them rebushed is a bit of a challenge but it seems to have gone OK. Going to invest in a colourtune set or maybe an analyser and check the mixture.

[@roundtailrestoration]

I hated centering the jets!

[@robfernie4632]

I've had the diff out twice on my 1500 its been back to a well known triumph expert in the UK and it still has a clonk when taking up the drive.I can't face taking the damm thing out again so have decided to live with it for now. Great video's

[@roundtailrestoration]

Thanks, Rob. I have a spare that I'm going to try to rebuild at some point. Not sure when because it's supposed to be pretty complicated with several special tools, but what the hell, I'll give it a shot!

[@djwallington2497]

Great detailed video, thank you. I’m currently restoring my Spitfire 1500 and having all the problems you have experienced so that makes me feel better that I’m not alone fixing one problem and finding two others. I Keep thinking I should start a video channel relating to my Spitfire’s story.

[@roundtailrestoration]

Glad you liked it. You should start. It's a great way to document what you're doing. I've gone back several times to review raw footage if I forget some items.

[@bshnabel]

Nice and detailed videos thanks

[@roundtailrestoration]

Thank you. Glad you liked them!

[@roselh1]

Chris, doesn’t the Spitfire have a return spring on the choke linkage? My big Healey and my Bugeye with HS2s use return springs to pull the fuel enrichment fully off. Lin

[@roundtailrestoration]

Hi Lin. There is a return spring, but it's integral to the shaft, not part of a separate assembly like the throttle return spring is. Mine are both there and they are installed properly, but they've always hung up a bit on me.

[@drmoss_ca]

"Aren't you finished yet?" Come on, it's a Triumph. You will never be finished.

[@roundtailrestoration]

Ha! Ain't that the truth! I'm sure I will continue to learn that time after time.

[@kathysarmcandy1992]

Keep in mind, the jet height static setting using the lift method, won't be accurate with the air cleaners on, unless you're running K&Ns or some other free flowing filters. I mark the jet nuts and body with a sharpie dot, so after the cleaners are on, I can accurately move a flat a time, if you need to go a bit leaner. Then you're down to plug color, unless you're using a wide band O2 sensor kit to tune it, oil weight, needle profile and spring rate. Just another hour or two 🤓

[@roundtailrestoration]

Fun, ain't it? I think I need to re-tune them again. Plugs are a bit black for me, not that nice grey-brown color.

[@roselh1]

Hi Chris, question for you. I believe in your video you turned down the jets 2 or 2 1/2 turns. That lowers the jets about .63”. In looking at technical tips from MiniMania, they also say to lower 2 turns but they specify to 1/8” or .125.” Of course, this does not make any sense. Did you measure the drop in the jet once you completed tuning your carbs? Closer to .65” or .125”? I think you ended up turning down your jets quite a bit as you tuned. Perhaps the .125” is correct? I am working on my son’s Bugeye which I haven’t done for years. Thanks so much! Lin

[@roundtailrestoration]

Hi Lin. I did not measure anything, I just followed the tuning guide directly from SU (sucarb.co.uk/technical-hs-type-carburetter-description-adjustments). There's also another resource you can find online, but it's about the same. If I'd have to guess, though, I think it's probably closer to the half-inch (.65") than it is the 1/8" (.125").

[@comfort_in_discomfort]

From my Z days I would always have Ztheraphy on call. Lots of good SU carb expertise there should you need.

[@roundtailrestoration]

Always looking for references. Thanks!

[@roselh1]

Chris, I am sorry but I could not find the video I was thinking about. Moss has choke return springs. Try one on the the front carb choke lever (opposite the same lever on the rear carb that has the cable link. I think you will find that while the choke may be a little harder to pull, the spring will fully close the idle enhancement. See what you think.

[@roundtailrestoration]

Ok, I'll check it out.

[@roselh1]

Chris, yes, my Bugeye HS2’s also have internal springs, but the Sprite still uses a separate spring (third spring) and this really makes a difference in fully closing off the idle enhancement. I will find a video showing the three springs and post it here. Lin

[@roundtailrestoration]

Awesome. Thanks, Lin, that would be much appreciated.

[@specter578]

Hi Chris. First of all, thanks for all of your restoration videos. I have just acquired a 65 Spitfire thats very similar to yours and ive been going through all of your helpful videos. I think the prior owner did all of the carb tuning and the car starts and runs. However, my idle is around 550. Id like to raise that to 850. Can i just turn those two screws by the top of each carb an equal amount without disconnecting the linkages and re-tuning the carbs?

[@roundtailrestoration]

Yup, assuming they were properly balanced, you should just be able to turn the screws incrementally, the same amount each, until you get the idle you want. Thanks!

[@njaahkbackyardbodyworks1807]

hey Chris...the DMV is the DMV...does not matter where you go...lol nice job on the carb tune...I have always wanted to get the vac-u-tune tool but have always just done the shop manual and the o'l ear-o-phone and just listen to the...tic tic tic of the engine and watched the RPMs...the clunk you hear in the rear....mine does it too....could just be a spitty thing...I got mine on the alignment rack at work and darn if the alignment machine had all the specs for an alignment in the database...i was surprised....so I aligned the rear and found out i need to find me some of the shims for the lower control arms in the front to get rid of the positive camber so i will quit wearing out the outside of the front tires....lol Keep up the good work....good luck with the DMV!!!

[@roundtailrestoration]

Thanks, Robert. Good to hear from you. Hope you and the family are well!

[@poppydogz]

I've been trying to find out for over a year what the rubbing sound is on my MK VI and I'm still no wiser.. I have come to the conclusion that that is how they sound lol Thanks for all you Video's Chris, much appreciated..

[@roundtailrestoration]

Lol, you're probably right! Thanks.

[@andreasmartensson768]

Good to see that those carbs got tuned even a little better this time, when you have done it 20 times more it will probably go much quicker :). I can recommend for others to watch all 3 chapters, there is a lot of good comments and information on what could go wrong while setting it up and what restorations that are needed to make sure that there is no air leakage. Most of us that have tried to tune this SU carbs from start will recognize the needed steps and if you are still uncertain on how to perform a step and the expected response from it, you will get it from this videos. Thanks again for charing, this is a 5-star channel

[@roundtailrestoration]

Thank you, Andreas!

[@barry6274]

Wow lots of detail work on the Carbs, glad you have it smoothed out and at a good idle. Drips of oil are always fun to try and get rid of with these British cars. I'm sure you will succeed with a little more time.

[@roundtailrestoration]

I'll give it a shot, Barry. But, I've got to have some oil leaks, I guess. When the leaks stop, that means you're probably out, not fixed!

[@grahamjohn331]

Great video Chris, I will call on you when my TR2 carbs are ready for set up in a year, or 2, or 3....

[@roundtailrestoration]

Lol, sounds good!

[@TornadoCAN99]

Looks like you could use a Gunson ColorTune spark plug to check the mixtures.

[@roundtailrestoration]

I definitely considered it. I think I've got it pretty good right now, but it's still something I may invest in in the future. Thanks!

[@dbarr15]

So, how did it go at the DVM?

[@roundtailrestoration]

I go Thursday, so I'll get an update then.

[@dbarr15]

@@roundtailrestoration Good luck.

[@roundtailrestoration]

Thank you!

[@ericpfiffner5615]

I hate to tell you this, but I'm a bit thankful for the oil leaks, I was starting to worry that I wouldn't have anything to watch soon! She sure sounds nice now with the tunes carbs and that lovely characteristic clickety-clack valvetrain. Good luck with the DMV, it was foolish of me to think it would go smoothly..

[@roundtailrestoration]

Yeah, I almost had it registered. It was actually the owner of the dealership that stopped it, come to find out. Oh, well. Hopefully I'll get the temp and bring the car back for the VIN verification and I'll be all set! Just in time for winter :(

[@ericpfiffner5615]

Well you're getting the soft top scrubbed up, so you might be able to get some cruising in before the salt comes out. It's going to be the longest winter ever waiting to drive her.

[@roundtailrestoration]

Hope so. Yes, a very long winter.

[@coom0004]

nice video..thanks

[@roundtailrestoration]

Thank you!