Need help (1972 240z)
 

I am in need of some help. I am trying to get these SU carbs adjusted properly but am not having any luck right now. It seems that I can really only get the car to stay running with the choke on which is then causing an over rich condition and then fouling the plugs an causing me to need to clean them to get the car running again. It is a 72 240z with both a mechanical and electric fuel pump (carter 60504) I installed the electric fuel pump because i was getting a vapor lock issue. I have done the following > new rings (yes i honed the cylinders), head job (bent valve when i got the car), all new gaskets and seals, a set of rebuilt su's to replace my very old and worn SU's, gas tank was cleaned, I have adjusted valves cold so i know I still need to adjust them when at normal operating temp I just need to find the time. right now i have the mixture nuts loosened out 1 and a half full turns. With the choke on (all the way which i know opens the butterflies a bit more) I am idling at about 13-1400 rpm. I have about 120 psi on all cylinders which sounds low, but I really haven't had a chance to really break-in the engine after the rebuild so I am not worried about that at all. My float setting is roughly 23mm but doesn't appear to be over that (i'm using the clear tube method). She sounds great when she is running, but as soon as put the choke down it starts to choke and spit and then die. Every so often when I'm revving the engine the front carb spits out some gas/air. It's also got some wet sooty residue on the face of it because of that. I'm in Vienna/Parkersburg, WV. If anyone is willing to come help me that'd be great. If anyone has any advice as to what may be going on please let me know. Oh and the cap and rotor and coil are all just a little over a year old or less and they look perfectly fine. Thanks

Ben

The S U carb is probably the easiest carb besides a lawn mower. First make sure the piston will move upward with your finger and drop smoothly back down. The main jet is what you adjusted to the 1- 1 1/2 turns. When the choke is pulled the jet tube moves to full rich. It has to return with choke off but if it is gummed up it won't return. The choke linkage must be free also. Don't be afraid to take it apart, just be careful. You don't really need a rebuild kit unless parts are destroyed with age. I had the same symtoms with a set of carbs that had been sitting for 12 years.

http://www.ztherapy.com/products/videos/just_SU.htm
SUTuneUp

I know all of that stuff. I just wonder if my float settings may be off. I've done the clear tube thing to check for 23mm down from the top of the float bowl (not the lid) and it appears to be at least very close. But it runs just with the choke on and when I put the choke off, the car sputters and slowly just dies on me.