Author Topic: Idle problem and stumble at 1400 rpm in 4th gear.  (Read 1969 times)

Offline 455bird

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Idle problem and stumble at 1400 rpm in 4th gear.
« on: December 16, 2013, 08:10:54 PM »
Looking for a little help here. I just rebuilt a 1976 Q-jet #17056512 for my 69 Firebird with a 462 Pontiac engine.  bought Cliff's book and a kit from him.  Cam duration is 239/247 @ .050", comp ratio is 12:1, ported #13 heads (flow 255cfm @28" H2o), 3.73 rear gears, 200R4 trans.  Setup on carb is:
idle tubes                       .041
idle down channel          .0635
upper air bleed               .070
lower air bleed                .070
idle bypass air                 .1065
mixture screw holes         .1065
holes in plates                  none
main jet                            77
primary rods                      44
secondary hanger             M
secondary rods                 DA

The engine idles slow 650 rpm and rough with 14 degrees of initial timing.  Vacuum advance is disconnected.  Engine pings with this much timing.  Exhaust stinks too.  turning in of the idle speed screw causes rich idle with black soot coming from tail pipes (nozzle drip?).  Idle mixture screws will kill engine if turned all the way in.  Seem happiest at 4 turns out (engine slightly speeds up at tip in).  APT set at 3.5 turns out.  I'm getting a terrible surging at 1400-1600 rpm in 4th (overdrive) with converter locked up.  I'm working with the third recipe from the book.  Why is it so difficult to get the idle rpm's up and a decent idle and what is causing the surging at cruise rpm's?

Offline Cliff Ruggles

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Re: Idle problem and stumble at 1400 rpm in 4th gear.
« Reply #1 on: December 26, 2013, 04:01:52 AM »
Raise the APT up some for the surging. 

Pretty hefty idle fuel delivery, raise the idle speed and look for nozzle drip and trim the mixture screw out at the desired idle speed.....Cliff