Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

No RPM increase

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78anniversary:
Hello all, i have a stock 78 corvette with a 17058204 that i rebuilt this spring.  The carb is rebuilt to stock specs and has ran great up until yesterday.  I pulled on the the expressway last night and mashed the pedal to the floor, when I thought the secondaries should just be opening, right about 3-3500 rpm, the motor just went flat and stopped increasing power and wouldnt accelerate and increase rpm from that point.  driving the car it accelerates fine under normal driving conditions, as long as i dont ask for the secondaries, once the pedal is pushed to activate them, then it flattens out...

where do i start?  its funny, it ran great last time i drove it. 

73 Z28:
It sounds like the small holes that feed fuel to the secondary fuel wells are blocked preventing fuel from feeding the secondaries when you get into the throttle. To fix this your going to have to remove the airhorn and remove the float, then you'll see 2 small holes about 1/4 inch off the floor of the fuel well one on each side. These allow fuel to flow into the secondary wells. These holes can be cleaned out with a .040 drill bit using a pin-vise. While you have the airhorn off, you should also readjust the spring tension on the airvalve to about 5/8 turn after the screw makes spring contact, and inspect the smaller brass tube ends that hang down from the airhorn. Make sure these aren't restricted, but if they are, use a .036 drill bit to clean them out. Then reassemble and test drive.

Paul

Frank400:
I'm thinking secondary lock-out.  Throw this away.

429bbf:
78  start simple .warm it up and pull the air cleaner and rev it up by hand and see if the secondaries are tring to open.if there not see whats stopping them.if they are then id look for a fuel problem . just my 2 cents. dean

78anniversary:
Thanks guys  i took it out this morning for a drive with the air cleaner removed, so i could hear if the secondaries are opening, and they are.  But as soon as they open is when it goes flat.  Im thinking its not getting fuel, because if it it got too much fuel it seams it should finally catch up and go.  But it doesn't, just stays flat.  I guess I'll try what 73 Z28 mentioned and make sure its got fuel in the bowls back there. 

Any other suggestions please chime in.

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