The more you watch the more you understand that little SU is a much more complex and clever bit of kit than first thought……..and the hours you must have spent fettling and playing with them over the years is probably immeasurable lol. Looking forward to the next part, if not before the new year Merry Christmas AC 👍🏻
Thanks AC. Love your stuff, no 'kin waffle - proper info. Guessing that explains why (0.100 needles anyway) all seem broadly the same at needle's thicker end, stations 1-4.
thanks AC. I am beginning to get a grasp on the complexities of SU tuning (HS4s on a '67 BGT here). How about a recording wide band gauge that could plot lambda against throttle position as you drove the car through a range of engine speeds and loads. Could analysis tell you whether you should change or modify the needle ? John in Manitoba, a long way from you.
Great explanation, really enjoyed that thank you. Quick question, how accurate is the jet sizing with relation to production? Does this need to be considered with relation to needle adjustment?
When you mention different positions of needle for different RPM, i assume you mean different airflows as for example a large throttle angle at 4k may be the same airflow as a smaller angle at 6k but both will raise the damper the same amount as its airflow lifting it versus the spring? And hence you can only pick one AFR for both of those situations even though in reality it might be better to be a little richer at WOT at 4k than at 2/3rd throttle at 6k as one is acceleration and the other is maintaining a constant speed on fast cruise?
It’s a challenge, and for that reason, in teach people to tune single carbs first, it they can then move onto twins once they have mastered the art of needle modification.
...Do I now have a claim to fame as I was sat opposite Don at Burlen when he wrote the advice section 'Choosing a different needle' for the Profile Chart?. Unlike me , he's a very clever chap!. 🙂
Although it now could do with updateing to include the need to use measuring equipment to track your progress and the dangers of engine damage due to over and under fueling
@@ACDodd He wrote the guide back in about 1991/2. We'd been proof reading and using Burlen's first edition S.U catalogue before the profile booklet was printed.
@@ACDodd I'm assuming no changes have been made to the original advice which was based as you've mentioned on mathematical area changes and not on flow data / rolling road. So purely a guide. You've gone to the next level with practical application. A lot has changed over the years, in particular the fuel. In 1986, the lead content in UK petrol was reduced by 30% and isobutane added. This certainly caused a few issues with pre-ignition, fuel vaporisation on many vehicles.
Brilliant explanation A.C, Very informative as always.. Thank you 👍
The more you watch the more you understand that little SU is a much more complex and clever bit of kit than first thought……..and the hours you must have spent fettling and playing with them over the years is probably immeasurable lol.
Looking forward to the next part, if not before the new year Merry Christmas AC 👍🏻
That’s the point most overlook it’s apparent simplicity.
Thanks AC. Love your stuff, no 'kin waffle - proper info. Guessing that explains why (0.100 needles anyway) all seem broadly the same at needle's thicker end, stations 1-4.
Well they are different by the difference is in the tenths of thou range.
Brilliant... Thanks AC!
My pleasure!
thanks AC. I am beginning to get a grasp on the complexities of SU tuning (HS4s on a '67 BGT here). How about a recording wide band gauge that could plot lambda against throttle position as you drove the car through a range of engine speeds and loads. Could analysis tell you whether you should change or modify the needle ? John in Manitoba, a long way from you.
You could do that but a lot of people like to try and get way to much data, and that’s an example, you don’t need to do that in reality.
Great explanation, really enjoyed that thank you. Quick question, how accurate is the jet sizing with relation to production? Does this need to be considered with relation to needle adjustment?
Yes I does vary but only in the tenths of thou range and yes it’s one of the reason that there are wide variations in fueling curves from carb to carb
When you mention different positions of needle for different RPM, i assume you mean different airflows as for example a large throttle angle at 4k may be the same airflow as a smaller angle at 6k but both will raise the damper the same amount as its airflow lifting it versus the spring?
And hence you can only pick one AFR for both of those situations even though in reality it might be better to be a little richer at WOT at 4k than at 2/3rd throttle at 6k as one is acceleration and the other is maintaining a constant speed on fast cruise?
No the reality is there is no overlap on needle stations.
S U perb.......thanks for that 😎
Glad you like it!
Brilliant explanation, thanks. How challenging is it with twin carbs to modify the needles by the same amount?
It’s a challenge, and for that reason, in teach people to tune single carbs first, it they can then move onto twins once they have mastered the art of needle modification.
...Do I now have a claim to fame as I was sat opposite Don at Burlen when he wrote the advice section 'Choosing a different needle' for the Profile Chart?. Unlike me , he's a very clever chap!. 🙂
Hehehehe maybe!
Although it now could do with updateing to include the need to use measuring equipment to track your progress and the dangers of engine damage due to over and under fueling
@@ACDodd He wrote the guide back in about 1991/2. We'd been proof reading and using Burlen's first edition S.U catalogue before the profile booklet was printed.
Nb. If Stan is still there, he'll remember as he was our manager.
@@ACDodd I'm assuming no changes have been made to the original advice which was based as you've mentioned on mathematical area changes and not on flow data / rolling road. So purely a guide. You've gone to the next level with practical application.
A lot has changed over the years, in particular the fuel. In 1986, the lead content in UK petrol was reduced by 30% and isobutane added. This certainly caused a few issues with pre-ignition, fuel vaporisation on many vehicles.