CArFAn Posted July 20, 2008 Share Posted July 20, 2008 My car is a 73 240z it has msa 3-2 headers and full 2.5in exhaust. There where flat top su's on it but i took them off for a set of round top su's. The first set i put on had the car running fine but went out of adjustment so i thought. So i spent a whole day trying to get them set right only to find out something was wrong with the rear carb, it wasn't pulling air in. So today i swapped those out for a set of z therapy round tops and i didn't mess with the settings and the rear carb is still not pulling air. If anyone can help out I'd really appreciate it. I need my car running its the only one i have until October. -Carfan Quote Link to comment Share on other sites More sharing options...
CArFAn Posted July 21, 2008 Author Share Posted July 21, 2008 Let me rephrase what i'm asking. I am running roundtop SU's on my car. For some reason the front one is sucking in air and the rear one isnt. This is causing my car to run very bad and undriveable. All i would like to know from anyone here is a suggestion as to what might be going on. At first i thought it was the ignition system so i JUST put in the electronic dizzy and it allowed me to drive down the street and back with the same but less hesitational like problem. I parked kept the car running and its still not pulling any air in. I don't know what else it could be. I was messing around with it just now and if i put the choke on then it pulls air in, but it shouldnt need the choke on to pull in air, the front is doing it with the choke closed. If you have a suggestion please let me know -Carfan Quote Link to comment Share on other sites More sharing options...
Skids260 Posted July 21, 2008 Share Posted July 21, 2008 I had the same problem. Turned out that the rear carbs float was set to high and not letting any fuel in the bowl thus it was only running on three cylinders. Quote Link to comment Share on other sites More sharing options...
SHO-Z Posted July 21, 2008 Share Posted July 21, 2008 You might have a stuck piston in the carb. Put your finger in the carb as see if the piston moves freely. If the carbs have been sitting around for a while they could be varnished up and all sorts of things could be plugged. Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 21, 2008 Share Posted July 21, 2008 Likely the synchronisation of the carburettors is screwed. If you haven't set it, and set the throttle stop screws for the proper idle speed and idle airflow, your carbs will not suck air. A suction piston will not cause this at idle. You have to work hard to stick a suction piston. Idle speed screws are for setting idle synchronisation, the screw on the crossbar linkage between the carbs is set for off-idle synchronisation. You need to check both with an airflow meter or mercury manometer. Read the applicable FSM section, or watch the Z Therapy Video---both should get you through synchronisation and on your way towards the next step in the engines' carb tuning process: Mixture Adjustment. Why do I say "synch"---when you pull the STARTER LEVER (it's not a choke on the Round Tops...it is on the Flat Tops, though...) you move the jet down and use a cam to activate the throttle plate and move it off the stop the idle speed screw sets it at. If you aren't sucking air with the starter system off, and ARE with the starter engaged...it means you have to open that rear throttle plate somewhat and let the air through. Quote Link to comment Share on other sites More sharing options...
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