SU Carb Tuning re-visit
Posted: Sat Apr 06, 2019 4:31 pm
While waiting for more parts & tools to arrive ( to finish the cooling, alt-swap & dizzy upgrades ), I decided to do some searches, to see how little I knew regarding SU tuning. As I noted in previous posts, I have balanced the carbs many times, however my "procedure" used only the Uni-Syn, a rubber hose ( to listen to the sounds at the carb throats ) & the "feel" & drop-rate of piston-lifts.
I have learned from the SU Gurus on this forum, that to cover the bases, I should also use the Color-tune tool & probably & O2 sniffer at the exhaust. I also learned that I should give up the search for 20 Wt. oil for the dashpots, & go for a mix ( proportions depending on climate & driving habits ) of ATF & Marvel Mystery oil. Nismou20 in Pasadena ( my closest neighbor ) said he used a 50/50 mix.
The post on the subject by nismou20 in 2017, got me thinking again about needle selection & matching parts. I went down in my shop & pulled out a couple of old ( and carbon-caked ) needles, to see if I could find any identifying marks on the mounting surfaces. With reading glasses & library-strength magnifying glass, the only marks I could see, were the old set-screw marks. Do I just need a stronger magnifier, or can needles only be identified by mike-ing down the length of the needle at prescribed intervals? My needles were only replaced once ( years ago with replacements from Dean A. ).
Nismou20 also remarked that the domes & bodies of the SUs should have matching numbers. Being lazy I didn't bother tryin to clean up one of the bodies on my carbs, but I did scrub-down and wire-brush the dome of the front carb, & again could find no numbers or other identifying marks on the outer surface. Are numbers on some inner surface, or am I really half-blind?
Any new info on needles, numbers or SU tuning in general will be appreciated.
Garry S.
I have learned from the SU Gurus on this forum, that to cover the bases, I should also use the Color-tune tool & probably & O2 sniffer at the exhaust. I also learned that I should give up the search for 20 Wt. oil for the dashpots, & go for a mix ( proportions depending on climate & driving habits ) of ATF & Marvel Mystery oil. Nismou20 in Pasadena ( my closest neighbor ) said he used a 50/50 mix.
The post on the subject by nismou20 in 2017, got me thinking again about needle selection & matching parts. I went down in my shop & pulled out a couple of old ( and carbon-caked ) needles, to see if I could find any identifying marks on the mounting surfaces. With reading glasses & library-strength magnifying glass, the only marks I could see, were the old set-screw marks. Do I just need a stronger magnifier, or can needles only be identified by mike-ing down the length of the needle at prescribed intervals? My needles were only replaced once ( years ago with replacements from Dean A. ).
Nismou20 also remarked that the domes & bodies of the SUs should have matching numbers. Being lazy I didn't bother tryin to clean up one of the bodies on my carbs, but I did scrub-down and wire-brush the dome of the front carb, & again could find no numbers or other identifying marks on the outer surface. Are numbers on some inner surface, or am I really half-blind?
Any new info on needles, numbers or SU tuning in general will be appreciated.
Garry S.