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78 Trans Am ideling @ 3000rpm

This is a discussion on 78 Trans Am ideling @ 3000rpm within the General Help forums, part of the LSx Technical Help Section category; So i have this 1978 Trans am with the 400 and 4 speed manual. Not long ago i switch out ...

  1. #1
    Member 10erg01's Avatar
    Join Date
    Nov 2009
    Columbia, Mo
    1998 Firebird Formula

    78 Trans Am ideling @ 3000rpm

    So i have this 1978 Trans am with the 400 and 4 speed manual. Not long ago i switch out the stock intake mainafold for a edlebrocker high preformance intake mainafold. when i got it all done and started it up, it was ideling at 3000rpm!!!! I know it has something to do with the carburator because i was not so sure when i put it back on if i put it on right. Most likly is it is a vaccum hose that i have hooked up wrong or the springs are in the wrong place.

    Picture of the carb as it is now, let me know if you would like better pics.

  2. #2
    Exalted Cyclops 67CamaroRSSS's Avatar
    Join Date
    Feb 2007
    San Diego, CA

    2002 Z28 A4 NBM
    Sadly now demodded :(

    It appears that your using the stock Q-jet cab. Is the idle speed screw set properly? Any change in the position of the carb (height wise as well as fore and aft) will alter the length of the cable which may require you to alter the idle speed screw.

    Is the choke "pulled off" or is it still set? This will cause a high (although not 3k rpm) also.

    Are the F/A mixture screws set properly? Stock cast iron intake is quite different from an Al aftermarket intake.

    Last (but not least) do you have all the vacuum lines set properly? Power Brake booster line sealed correctly?

    Also, is the distributor in correctly and the timing set properly?

    As you can see there are a lot of things can go wrong with just an intake change.
    67 Camaro: K-K + 797-z (look it up), 454/Th400/4.10 12-bolt = 6mpg, PS/PDB/PW tilt, tach, gauges...

    2005 Corvette LS2/M6 Magnetic Red Metallic (What else would it be?) w/ Cashmere interior

    2002 Z28: NBM/Tan, MTI smooth lid, smooth bellows, !AIR, !cats, 1-3/4" QTP SS LT's, 2-1/2" TD's with X-pipe, MagnaFlows dumped at axle, custom welded SFC's, MidWest Chassis body mount adjustable T/A, 3400 stall, 3.23 gears (was 2.73). Tuned: 343rwhp/357rwt (before TD's). Best: 12.559 @ 108+, 1.73 60' @ 3500' DA w/MT ET Street DR's.

    Carbon footprint? CLOWN SHOE!

  3. #3
    Member 10erg01's Avatar
    Join Date
    Nov 2009
    Columbia, Mo
    1998 Firebird Formula

    I wish i could answer your questions, but when it come to carburators i am a begginer and know very little. If you know of some books or something or info i could read. Also you by chance don't happen to have or know where to get a picture that is very detalited that shows where the vaccum lines are supposed to go. The new intake i put on got rid of the EGR system so i probabley misplaced some of them. Also if do you have a picture that shows how a carb is supposed to be installed?
    Thanks for all the help!

  4. #4
    Junior Member
    Join Date
    May 2009
    Santa Maria, California

    1998 Pontiac Formula LS6

    It looks like you put a spreadbore carb on a squarebore manifold. If so, that's a big OOPS. You'll need an adapter plate. This idea just came to me since it's been a long time since I swapped out carbs.

  5. #5
    Junior Member speedfreak1's Avatar
    Join Date
    Mar 2011

    1999 trans am

    looking at that pic it looks like the idle speed screw is turned all the way in and still not touching the tab there is a gap. try disconecting your throtle cable and make sure the carb is going all the way back closed. I had a 76 ta and put a edelbrock performer intake on it with the stock carb and had no problems except the shaker scoop sat a little lower when mounted to the carb.

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