SU needles and tuning

[blitzkraig]

I have two sets of SU carbs, one 3 screw, one four screw. The three screws are what I have on the engine currently and they run just great. I polished and rebuilt the 4 screws to put on and just tried to tune them. However the idle adj screw is screwed in all the way and the car is still running extremely rich (the sparkplugs are black). The only idea I have is that I have the wrong needles in the carbs. The rebuild kit I got is made by Beck Arnley World Parts (from a good auto store, not kragen) and it came with two sets of needles. The only differences I see on them is that two are marked with HWJ1 and the other two HWJ2. I've read many posts on how to tune these and I have no idea what to do now.:cross-eye

[blitzkraig]

Ok. Since I never had any pictures showing the needle position, I thought I was supposed to sit the needles all the way down til the step isn't showing. Durh, back to tuning. Well I start off with the throttle adj screws in about 1.5 turns and the idle adj screws out two turns. I end up with the throttle screws both all the way out until they don't make contact and the idle is still about 1000 rpm, I'm ok with that. So I move on to the idle adj screws. Push the lifting pin slightly and the rpms go and stay up. So I keep screwing in the idle adj screw until it stops and it is still running rich! ACK. I give up for the night and am putting back the dirty 3 screws. Any ideas for this weekend?

[beandip]

It sound like a vacume leak may be the trouble. When you had the carbs apart I hope that you dident swap any parts from one carb to the other . The pistons are fitted by the factory . Now did you loosen the butterflys by chance.? One cause of the trouble you are having is air leaking around the butterfly . Take the carb and look through the throat and with the throttle closed and see if you can see any light around the edges of the disk. If you do you must adjust the disk so it will seal and not allow any light, air , to pass around it. Here is how you do it , loosen the screws just enough so that the disk will barely move , now close the throttle firmly a couple of times and take a look against a light and see if it seals , when you get a seal tighten one of the screws and check again . If it dident slip and it seals remove the loose screw and put some lock-tite on the threads and insert and tighten it, and then do the same with the other one. Another thing to check before you remove the carbs is to stick your finger in the throat and lift the slide, piston , and let it drop , it should drop with a clunk , if it does not remove it and clean it and remove any grit or dirt. I use 20wt oil in the dampner , by the way. be careful not to bend the needle !:classic: Let me know what you find. Gary:classic: