TR Rob Posted November 25, 2023 Report Share Posted November 25, 2023 Have acquired a Gunson Colortune and intend to check the air/fuel mixture on the SU carbs. on my TR3A. I suspect the engine is running a bit rich. I’m hoping this will be a relatively straight forward job, but judging by other straight forward jobs on this car, I am realising on a 63 year old car nothing is straightforward. If anyone on the forum has any tricks or techniques for this operation I would be grateful to receive them. In anticipation…….thanks Quote Link to post Share on other sites
Lebro Posted November 26, 2023 Report Share Posted November 26, 2023 (edited) You are aiming for a blue flame , just on the edge of turning yellow. Solid blue is too lean, solid yellow is too rich. Don't forget to clean the glass bit after every use. Bob Edited November 26, 2023 by Lebro Quote Link to post Share on other sites
TRier Posted November 26, 2023 Report Share Posted November 26, 2023 (edited) Hi Rob, I’ve recently overhauled the H6 SUs on my 3a and tuned it with a colour tune, very impressed with it. I tuned it initially according to the “instructions” on the overhaul kit from SU and admittedly in a hurry. It ran quite well, I had done a lot of work to it so went on a 500 mile shakedown, nice and responsive to drive, 23 mpg, not very impressed with that. Got a colortune kit and re tuned it, couple of videos attached here, one showing number 1 running too rich and the second one showing it pretty much right. After re tuning with colortune I went to Spain for 10 days, 1800 miles, full luggage, 2 up and roof down, I did two tests over th 1800, 35.5 and 35.7. The speedo is right. So videos showing the colours aside, I found that the front carburettor was very fiddly to get right. It did not adjust as easily as the rear one, tended to max out the mixture screw and then with it maxed out be close to right but not perfect. I was loath to take the carb out and do a realignment but in the finish I had to, it took a couple of goes to get a nice linear smooth dropping of the piston on that carb, I almost gave up on the basis that something was wrong with it but luckily in the finish it came right. Then with the piston dropping nice and smooth the mixture adjustment worked properly, it required a bit of fiddling. The other thing that’s important is to use the two little spanner’s that SU give you or make one, you have to lock the adjustment base with a spanner when adjusting the back nut and it’s a bit awkward, if you don’t hold that outer hex whilst adjusting the backnut then it’s difficult to get repeatable results. I haven’t put an AFR analyser on this thing yet but I will at some point but the mpg and it’s performance in mountainy country would indicate it’s pretty much on the money. Worth all the effort though. Hope that helps. Approx Correct Mixture.mp4 Rich Mixture.mp4 Edited November 26, 2023 by TRier Typo Quote Link to post Share on other sites
Lebro Posted November 27, 2023 Report Share Posted November 27, 2023 Click on to enlarge This shows how mixture can vary between cylinders fed from the same carb Bob Quote Link to post Share on other sites
TRier Posted November 27, 2023 Report Share Posted November 27, 2023 7 hours ago, Lebro said: Click on to enlarge This shows how mixture can vary between cylinders fed from the same carb Bob Hi Rob, that's an interesting one. What did you find that down to? Quote Link to post Share on other sites
Lebro Posted November 27, 2023 Report Share Posted November 27, 2023 Nothing definite, maybe because the engine is at an angle (& even more so in my garage which is on a slope !) & the fuel runs down hill in the manifold ? who knows. Bob Quote Link to post Share on other sites
Ian Vincent Posted November 27, 2023 Report Share Posted November 27, 2023 I’ve noticed the same thing. My inner two cylinders run slightly richer than the outer ones. Rgds Ian Quote Link to post Share on other sites
Smithfire67 Posted December 1, 2023 Report Share Posted December 1, 2023 On 11/25/2023 at 6:24 PM, TR Rob said: Have acquired a Gunson Colortune and intend to check the air/fuel mixture on the SU carbs. on my TR3A. I suspect the engine is running a bit rich. I’m hoping this will be a relatively straight forward job, but judging by other straight forward jobs on this car, I am realising on a 63 year old car nothing is straightforward. If anyone on the forum has any tricks or techniques for this operation I would be grateful to receive them. In anticipation…….thanks Hi Rob How did using the Gunsom Colour tune go? I also have sooty plugs and am wondering which the best plan of attack is? Many thanks Clive Quote Link to post Share on other sites
TR Rob Posted December 1, 2023 Author Report Share Posted December 1, 2023 (edited) 7 hours ago, Smithfire67 said: Hi Rob How did using the Gunsom Colour tune go? I also have sooty plugs and am wondering which the best plan of attack is? Many thanks Clive…. bought a unit off EBay and it has only just arrived. Seems to be in good condition, but I have not used it yet, the main reason being my garage is so cold , I can’t muster any enthusiasm for being out there. I did buy the special SU jet nut adjusting spanner as a “normal”spanner would be difficult to use. If we get a bit of warmer weather I will have a go at adjusting the mixture and report back to the forum !! Edited December 1, 2023 by TR Rob Grammar Quote Link to post Share on other sites
Smithfire67 Posted December 2, 2023 Report Share Posted December 2, 2023 13 hours ago, TR Rob said: I totally know what you mean with enthusiasm Rob. It is particularly grim and cold out there in shed land at the moment! Clive Quote Link to post Share on other sites
TimG Posted December 2, 2023 Report Share Posted December 2, 2023 My Colour tune has a tube which clips on the plug hex & has a mirror so you can angle it to view plug over the engine while adjusting the carb. Quote Link to post Share on other sites
Smithfire67 Posted December 2, 2023 Report Share Posted December 2, 2023 51 minutes ago, TimG said: My Colour tune has a tube which clips on the plug hex & has a mirror so you can angle it to view plug over the engine while adjusting the carb. That's a good idea Tim. Did you find tuning this way to be effective? Quote Link to post Share on other sites
Keith Wigglesworth Posted December 2, 2023 Report Share Posted December 2, 2023 I recommend pointing the front of the car into the garage and turning the lights out as you tune. Use two colourtunes if you can. Go for the blue colour recommended by the instructions..I found this to result in a lean mix. I then richened a couple of flats and all was well. Keith Quote Link to post Share on other sites
Smithfire67 Posted December 2, 2023 Report Share Posted December 2, 2023 50 minutes ago, Keith Wigglesworth said: I recommend pointing the front of the car into the garage and turning the lights out as you tune. Use two colourtunes if you can. Go for the blue colour recommended by the instructions..I found this to result in a lean mix. I then richened a couple of flats and all was well. Keith Out of interest Keith, which cylinders did you pick to tune by? Clive Quote Link to post Share on other sites
Keith Wigglesworth Posted December 3, 2023 Report Share Posted December 3, 2023 I used no 1 and 4 Quote Link to post Share on other sites
TimG Posted December 7, 2023 Report Share Posted December 7, 2023 On 12/2/2023 at 5:07 PM, Smithfire67 said: That's a good idea Tim. Did you find tuning this way to be effective? The tube with mirror came with the colortune. It has worked well tuning my 1930 Sunbeam. With the TR you can see the view window but I have not yet managed to get it to run smoothly. Have new plugs to fit, I hope that improves running to get tune. Quote Link to post Share on other sites
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