Hi All-

Alright-I've replaced my aging SU's with a set of rebuilts. When I adjust to the proper mixture ar idle the car seems to run too lean at high speeds (I pull the choke out and performance is improved quite a bit). If I adjust the carbs to maximum performance at high speeds they're running way too rich at idle. What gives?

go to Ztherapy.com, or www.Vclassics.com.
SU are sweet and simple if you understand them. Ztherapy site is THE BEST
site, period. Yes z-cars used SU's for a while.
cheers--

k.i.s.s. check the presuure from your pump.. If it's low the car will idle great and lean out under load. Also the float level in the bowls. My experience has been that needles don't really effect things that much, but whatever. I suggeast the fuel stuff cause it,s easier to check, and IMHO a more likely culprit.

Wrong needles... general guideline for needles:

Stock B18D (low compression) = ZH
Stock B18B (high compression) = KD
Stock B20B (medium compression) = SM or KD
More motor than that = DX
Even more motor than that = don't use SUs

Why would compression affect which metering needle you use?

Cams and bore I could see since they would change the air
velocity or volume of fuel required, but I thought that squishing
the mixture more before buring it would be independent of how
much fuel is required for a given volume of air.
chris

I unhelpfully mentioned compression as an aid in identifying the different engine models. I don't know if CR does effect needle choice or not. Sorry for any confusion.

Thanks. I'll check the needle. Where would the two letters be written?

You have to take the domes off and remove the pistons. There's a set screw through the side of the piston that holds the needle in place. Undo that and pull the needle out. The letters are stamped on the surface that the set screw contacts.

If the needle doesn't want to come out, try wearing rubber dishwashing gloves to get a better grip on it. When you put it back in, note that it doesn't push all the way into the piston, but that the bottom of the mounting surface is even with the bottom of the piston.

Been a long time since I have messed with SU's, but sounds like the wrong needle on the carb. If you have your old carbs you might swap the needles from the vacuum pistons or just swap the entire piston assembly to see if that takes care of the problem. The taper of the needle directly influences fuel flow.

dick

this is a common problem or symptom on these. what happens is the needle a jet are worn in the closed position. if your needle wasnt worn it would give you proper mixture throughout the power range. most people just find a happy medium, but if you know someone who know how to rebuld them you could have them rebuilt. the throttle shafts are probably worn and the throttle stops are not working, usually i would say $650 for somebody who know what theyre doing.the throttle shaft bushings will have to be made on a lathe, they are no longer available.

Magoo: Check out Moss Motors online. ALL parts are available for the HS6 and relatively inexpensively. For example, the shaft bushings are about $3.00 each, and your choice of needles will run about $8.00 per. Look under the online catalogue for the big Austin Healy or the old Jaguar which used the HS6 in one variation or another. With Moss, a good many of the parts are NOS or are built to original specs just for them. They're having a sale now, too.

Brad

thanks brad, i havent rebuilt one of these in about 5 years. back then i used to make them up on a lathe in the backroom, i never heard about moss motors before.

Ok, Ihave two 122's and I love SU's, hey they work IF you understand them.
Piece of cake here--- my suggestion is to go to www.Ztherapy.com, or vclassics.
com for complete info. The main main thing is if you cannot adjust the mixture
settings from lean to rich (IE from min vacuum to max, or just listen to
your idle speed, if all is well you CAN hear a setting where idle goes to
high then drops down. Go back towards high a bit. then do the other.
Its best that you balance both carbs (or try to). I have 2 122's, 500k
betwixt the two, they are still our main drives, altho we just bought a 1999
V70. Now if you want complicated equipment, look at this cars diagrams or ANY
new car, any make. 122's will roll forever, parts are every where, simple
and mine are paid for.
any questions, mail me at boehme@hevanet.com
cheers