SU Carb Tuning - Part 2 | Roundtail Restoration

Back to the Spitfire. There will be another video dealing with carb tuning, but I'm going to try not to dedicate it to that. I'm still learning. I can driver her, but it ain't pretty!
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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[@TRRehab]

Great videos as always Chris. I finally got a lil interest in firing up the 57 TR3 after a year of sitting. I recorded the balancing as well as the color tune. Nothing as detailed as this, just like verifying that things are not too far off.

[@roundtailrestoration]

I was wondering where you have been! That TR3 of yours is just beautiful, I'd love to see more of it. Thanks!

[@bernhardlist9359]

hi Chris, the butterfly plates have to seal completely and the actual idle adjustment will be done with the bypass screw and a synchrometer.

[@roundtailrestoration]

I did a butterfly valve replacement in an earlier video. Got them pretty close. Not totally closed, but as close as I could get them.

[@andreasmartensson768]

Hello Chris, thanks for a fantastic channel and for sharing your jurney with this spitfire.

[@andreasmartensson768]

I own a Triumph spitfire4 myself and have had some nice evenings tunings those SU2 carbs. I still do not think it is perfect but if you want, I can send you a 16 step guide that I have written down for my own purpose together with pictures. I do recognize some of the steps that you do in the video but I am not sure if you get the last points right when trying to get air/gas mixture correct.

[@roundtailrestoration]

Thanks, Andreas. I responded to you blog post via my email. Appreciate the help!

[@roundtailrestoration]

Thank you. Glad you're enjoying it!

[@bernhardlist9359]

Chris, you don’t use the synchrometer to set the mixture but first you use it the set the airbypassscrew to have identical amount of air going through. Once you have the same air than you use the mixture adjustment as mentioned in the manual.

[@roundtailrestoration]

Yeah, I messed that up in this video. Concept error on my part. Thanks for watching!

[@ericpfiffner5615]

Can't wait to mess with my SU's, hopefully you'll have it figured out by then! I split my calipers too, moss has the quad rings for the fluid channel, at least for the 'B. Now if only every part that I need wasn't on backorder...

[@roundtailrestoration]

Yup, that's where I got my rings, too. Only people to have them that I know of.

[@barry6274]

Good information on the carbs. I hope the brake caliper is``A okay`` now.

[@roundtailrestoration]

I hope so, too. Thanks, Barry!

[@hecklejeckle1333]

Hi Chris. Good video quality. Can I ask - you seem to be adjusting AFR with the jet adjustment while using the air flow meter too. I couldn't understand the function of the airflow meter in this process. Everything else I've read or seen with SU carbys has the air flow (idle) adjustment and fuel jet (AFR) adjusted done independently. Air flow is adjusted on the 2 linkage screws (first) to idle speed then the fuel mixture ( rich or lean adjustment) is adjusted with the jet height adjustment . The fuel mixture is checked by using a Gunsons Colourtuner or the SU carby piston lift method (lift piston and engine dies then too lean. If accelerates its too rich). Can you please advise what you were doing with the airflow meter when adjusting the jet (AFR)? Cheers

[@roundtailrestoration]

Watching it again, I'm not real sure what I was doing there. My guess is that I had it in my mind that changing the tuning would change the engine running and I could use the unisyn to tell me how much that carb was sucking, maybe to compare it when I did the other one. I'd mark that one up to a rookie mistake.

[@grahamjohn331]

can you put a spring on to pull those jets back up?

[@roundtailrestoration]

Hi Graham. There are springs there as part of the normal linkage. I think it's an alignment issue.

[@grahamjohn331]

@@roundtailrestoration you will get it sorted.

[@ronwilkin7760]

choke problem is in the linkage adjustment

[@roundtailrestoration]

Like, linkage where it attaches to the jet, or between the carbs? My choke cable is really long, too, and I took care of that tonight...seems to operate more smoothly. Thanks, Ron.

[@ronwilkin7760]

@@roundtailrestoration when the choke starts to engage thats when yu put yu choke line tight

[@roundtailrestoration]

Thanks, Ron. I was wondering about that. The manual is exactly clear if I take up the slack in the spring or not before tightening the cable. That clears it up.

[@joeblogs8193]

Seeing you do the work makes me want to jump through the computer screen and help you. I have done 100's of them. Not sure from your video, but are you tuning each carb independent of the other? The spindles should be un-clamped so the throttle cable and movement of the carby has no influence over the other. The you can start to balance and set mixtures. After you have made adjustments, rev up the engine on that carby until perfect and them work on other carby and again, revving engine helps clear combustion chambers and makes sure butterfly spindle (idle speed) stop is seated. setting mixture can be done with small screwdriver under piston, slowly lift piston, engine speed will increase and go a bit more and engine revs will fall. while doing all this mix adjustment, you will need to trim the idle speed several time and make sure air flow is same on other carb, after that is correct go back to 1st carb and again check mixture and do same on last carb. And the LAST thing you do is tie the two carbs together with the pinch bolts on the center spindle. To get it perfect, its a lot of checking one carb against the other. One last thing, just fill the dashpots to the top or just under, they will find their correct level. Thanks for your videos.

[@roundtailrestoration]

Thanks so much for all the info and help, Joe! Yes, tuning the carbs independently (using tuning loosely). As for the dashpots, I assume if I do that, I would expect oil to overflow and eventually get sucked into the motor, right?

[@joeblogs8193]

@@roundtailrestoration such a small amount of oil will be burnt off in no time and not do any harm at all. Soon you will looking for a new project. Its been a great series you have done. Thank you.

[@roundtailrestoration]

Thank you, Joe. Appreciate the help.

[@DavidUKesb]

Hi Joe. Should the spindles be unclamped for BOTH the air balancing AND the mixture adjustment or only for one of these actions? I'll be tuning my HS4s soon, but will be using the SU tool kit for balancing (rods and wires) to enable to check air balancing at revs rather than just at idle. Unfortunately instructions don't say when doing if oil should be in dashpot or not.

[@roundtailrestoration]

@@DavidUKesb Hi David. Here's a Google Drive share link to the document I was using to tune my carbs. Hopefully this will answer your question (which I think is yes). Let me know if it doesn't work for you. drive.google.com/file/d/1_CNuroOmzaAAi-8uNvOZ4si7JqS6HJ0h/view?usp=sharing

[@cabdriveruk]

Great video Chris. Those SU's were always a bit of fiddle to set up and get right, but i think your almost there now. That caliper was a blow but at least you didn't spoil your new brake pads.Hope its fixed and dried up now. Cheers, Jeff.

[@roundtailrestoration]

Thanks, Jeff. I think the brakes should be good. I'll play with the carbs more. Understanding more each time, I think. We'll see!

[@ElfoDrow]

Thanks to you I repaired my double HS2 carburetor. Thank you so much. Greetings from Santiago, Chile.

[@roundtailrestoration]

Good deal! Thanks for watching from Chile!

[@paulmuff9883]

Wow 😱 you’re doing it completely wrong I hope you’ve learned from the comments on here and redone it correctly 🙏🏻😢😢

[@roundtailrestoration]

Definitely some black magic for me, still. But, I have done some more adjustments and think I've figured it out. Constructive, corrective comments on my videos is one of the biggest reasons I put the videos up - try to learn from those that have come before and have way more experience than I do. Thanks!

[@upland1826]

Very good video Chris. I'm just re-installing my HS2s on the Sprite and did the throttle disc dance for quite a while before I was satisfied. Now on to the tuning phase. Noticed your Rutgers water bottle. Stephen

[@roundtailrestoration]

Thanks for watching. I'm from south Jersey and my sister went to Rutgers.

[@dbarr15]

Chris thanks for the nice video. Did you replace the spindle of your carb? Was it worn? Did you replace the bushing the spindle rides in? The bushing is a PITA and apparently needs to be pressed in and a special reamer to get it to the right dimension. All those might be contributing to not being able to get the butterflies centered.

[@roundtailrestoration]

I did replace the butterfly valves and spindles. The hs2 models are the only ones that don't have a brass bushing, which is very convenient. It didn't feel like it is hanging up...until it gets in the car, of course!