Backfire Help!

[240zJon]

i have a 72 240z with a l28 in it that is running su's. it has the E88 intake on it. Well, when i start it up with the choke full it sounds good but once i take the choke off it starts to sputter and then die unless i pull the choke back open. Also when i drive it from a dead stop the car sputters and almost dies but if i pull the choke it saves it. I've put on a brand new intake/exhaust gasket and it still does it. Does any one have any ideas?

[Glitch]

It's a bit difficult to diagnose this without more information. Was the car running fine before hand, or has it just started running badly after replacing the intake gasket? Did you get the gasket surfaces clean and remove ALL traces of the old gasket? Have you changed any components like intake manifold, carbs, removed any vacuum lines?

 

Generally speaking, it sounds like you either have a large vacuum leak or your mixture is far too lean. Do the usual checks for broken vacuum hoses, check for air leaks around the carb gaskets and intake/exhaust manifold gasket as well. Look for cracks in the carb flanges where they meet the intake manifold.

 

I wouldn't suspect the mixture to be off unless you were messing with the mixture knobs when you had the carbs off. This procedure works well for the round top SU carbs: A good place to start with mixture is first to turn both the knobs all the way in, then back them out 1.5 turns. (Mixture knobs are located on the bottom of the carbs.) Make sure that you open the mixture screws exactly the same amount on both carbs. Get the car up to operating temperature and turn the choke off completely. Keep backing the mixture knobs out a 1/4 turn at a time until you obtain the fastest idle speed. If the idle drops, turn back in 1/4 turn. Re-adjust the idle speed and then fine tune the mixture again. I hope this helps. Good luck!