Hi,
I'm sorry to come once again to the topic of SU tuning but I could't find what I'm looking for in the archives and on the web... Here is my story: the piston in the front carb of my B20B didn't go down properly at idle, resulting in hectic idle revving and poor low-end acceleration: I have to play on the clutch to start... No good. I dismanteled it and found out the piston is free to go in the suction chamber, but it looks like the needle prevents the piston to go down (ie with the suction chamber taken off, the piston has to be forced down onto the bridge when the needle is on, and NOT when the needle is off). Very well I thought, so I took the needle off, rotated it a bit in the piston, made sure it was free (it's a newer carb with mobile needles) and its holder oriented correctly. Then I drove happily for 600 miles. And I'm now back in my problems: same symptoms... So what should I do exactly? is there a way of centering the jets on this type of carb (post-68, three bolt air filters) since I think this should do it? And how is this to be performed?? Or should I follow a different path? Thanks in advance, and happy new year to y'all!!!! Séb

Is this an HS6 or an HIF6?
On an HS6 put the carb top together with the needle sticking down, then put
the jet, jet sleeve, etc into the bottom around the needle, being careful
when tightening it up that the needle doesn't drag (work it up and down as
you sequentially tighten the plug in the bottom). When you get it good and
tight with the needle free, you should be ready to do the rest of the stuff.

On the HIF6 the jet is loose enough that this is rarely a problem. The
ones where it is really critical are the H4s where the jet actually goes
through some gasoline-proof packing so they have to be exactly centered.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma

Hi George, once again your advice did the trick... Thanks a lot! Seb