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  1. #1
    Join Date
    Feb 2005
    Location
    Copenhagen
    Posts
    141
    Country Flag: Denmark

    lean spot just of idle + 1 mixture screw not responding 4150 DP

    Hi I'm having a bit of problems with my 4150 double pumper with proform main body. Just of idle I'm having this very lean spot (20:1 on the AFR) if I hold the throttle steady it takes a second the it suddenly picks up (13:1) as if I hit a switch. This happens in neutral or under very light cruise. WOT is fine. The car has been running perfectly in this configuration previously. All I have done is: new spark plugs, spark plug wires, rebuilt carb (will take it apart again..) and igniton timing tune up (33 degrees total). I'm very aware of the transition slots. They are setup "square". Right now it idles at 1000 rpm. Sometimes during cruise I get some popping from the exhaust. I suspect a lean misfire getting burned in the exhaust?
    The other problem that leeds me to taking the carb off is that, all but one mixture screw kills the engine, when turned in. The last one (primary/passengers side) does nothing at all. I have an edelbrock performer RPM intake with an 1/2 inch open spacer.
    The engine is Pontiac 455 with edelbruck performer rpm heads, 041 cam, msd 6al ignition and msd probillet distributor with blue (middle) springs. slow advance springs have no effect.
    Hope you can lead me in the right direction I'm especially curious about the single non responding mixture screw (all I can find is ALL not responding)
    Best regards from Denmark - hope you understand my English



  2. #2
    Join Date
    Feb 2005
    Location
    Copenhagen
    Posts
    141
    Country Flag: Denmark
    well I managed to solve the problem myself. I took the off the primary metering block and blew all passages with compressed air. Something came flying when I cleaned the idle restriction passage. Now it runs great once again!!