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12 hours ago, stuart said:

Sounds as if a change of needle would be a help then John, needs to be slightly weaker at idle. You can compare needles here http://www.mintylamb.co.uk/suneedle/

Stuart.

Thanks Stuart. The needle comparison chart is great, but I'm not overly experienced in selecting carb needles always using the standard recommended ones.

These carbies have run rich since I fitted them, it is possible that they don't have standard jets so a different needle might be the answer.

Needle 61 appears much leaner at idle and slightly richer at higher revs. Have I got that right or is there a better option you would recommend.

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20 minutes ago, John McCormack said:

Thanks Stuart. The needle comparison chart is great, but I'm not overly experienced in selecting carb needles always using the standard recommended ones.

These carbies have run rich since I fitted them, it is possible that they don't have standard jets so a different needle might be the answer.

Needle 61 appears much leaner at idle and slightly richer at higher revs. Have I got that right or is there a better option you would recommend.

I also might try lowering the level in the float bowl and see what that does.

 

 

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I had similar trouble getting my carbs lean enough, still rich with the adjusters fully up (H6).  The carbs had new needles and jets, although to call them jets is probably wrong as they are a simple tube, and I think only come in the one size. Eventually I dropped the needles down about 2 mm out of the pistons and this did the trick, enabling me to wind down the adjusters and get a decent mixture colour with the colourtunes.

Possible after 60,000 miles your jet tubes could be worn, I suspected mine too and bought new, but it made no difference.

Also heard on here of owners dropping the fuel float levels to obtain a weaker mixture, as well as dropping the needles, so it seems as if many owners have the same problems setting these carbs.

I have got mine running good now, although it hesitates when pulling away until fully warmed up, so I am probably on the lean side, but plug colour looks OK after a decent run so leaving them alone for now.

Incidentally, the jet settings I ended up with are not the same on each carb, and I don`t think that matters. I have 2 colourtunes which I put in No`s 1 and 4 cylinders, and they show the same colours on tickover and through the rev range.

Ralph

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22 hours ago, Ralph Whitaker said:

I had similar trouble getting my carbs lean enough, still rich with the adjusters fully up (H6).  The carbs had new needles and jets, although to call them jets is probably wrong as they are a simple tube, and I think only come in the one size. Eventually I dropped the needles down about 2 mm out of the pistons and this did the trick, enabling me to wind down the adjusters and get a decent mixture colour with the colourtunes.

Possible after 60,000 miles your jet tubes could be worn, I suspected mine too and bought new, but it made no difference.

Also heard on here of owners dropping the fuel float levels to obtain a weaker mixture, as well as dropping the needles, so it seems as if many owners have the same problems setting these carbs.

I have got mine running good now, although it hesitates when pulling away until fully warmed up, so I am probably on the lean side, but plug colour looks OK after a decent run so leaving them alone for now.

Incidentally, the jet settings I ended up with are not the same on each carb, and I don`t think that matters. I have 2 colourtunes which I put in No`s 1 and 4 cylinders, and they show the same colours on tickover and through the rev range.

Ralph

Interesting as I've had a similar experience.

Since my last post I went back to basics and didn't assume everything was OK. I checked float levels, slightly too high. The needles were set with the bridge at the jet holder level not against the bottom of the piston.

I corrected both to the book and now I can get a too lean mixture at full up on the adjusting nut. Using the Colourtune I get a blue flame about 3 flats down so have set the mixture one flat further down with an orange flame.

I've been driving and playing with this car for 46 years and am still learning (or maybe re-learning) ways to make it perform properly. The car is driving better than it has for many years.

 

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  • 2 months later...
On 2/5/2022 at 6:52 PM, John McCormack said:

Interesting as I've had a similar experience.

Since my last post I went back to basics and didn't assume everything was OK. I checked float levels, slightly too high. The needles were set with the bridge at the jet holder level not against the bottom of the piston.

I corrected both to the book and now I can get a too lean mixture at full up on the adjusting nut. Using the Colourtune I get a blue flame about 3 flats down so have set the mixture one flat further down with an orange flame.

I've been driving and playing with this car for 46 years and am still learning (or maybe re-learning) ways to make it perform properly. The car is driving better than it has for many years.

 

After a short while the same problem, too rich at idle with the nuts all the way up and not rich enough at speed, returned.

I fitted a spare set of carbies I had and it transformed the car. Mixture can be set accurately, and it idles and performs really well.

I took the suspect carbies to an excellent SU man we have here and he just rang me that he has replaced the jets which were worn. He said there is no sign the needles weren't centred; it was just the amount of use that had worn the jets.

I will continue with the set on the car for a few tanks of petrol and then think about fitting the overhauled ones.

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