Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Rebuilt Carb, all bog except idle
Kjetil:
Hi
I rebuilt my second carb this winter with Cliff's HP kit. It was going on a Chevrolet Performance 454HO crate in my 1975 Monte Carlo. Cliff recommended to use the second recipe for the idle system. Besides that I modified the secondary side slightly. So the specs are:
Carb specs:
# 17080202
Choke removed and plugged.
Idle tube: 0,039"
Idle down channel: 0,059"
Lower idle air bleed: 0,07"
Upper idle air bleed: 0,07"
Idle screw holes have been opened up
Accelerator discharge holes: 0,031"
Main jets: 77
Rods: 44
Float level: 1/4"
Secondary POE well restriction: 0,039"
Secondary POE restriction: 0,059"
Secondary tube restriction: 0,036"
Secondary flaps are notched, and the spring tension is 3/4 turns. Choke pulloff is new from Cliff and unmodified.
Engine specs:
Compression ratio: 8.75:1
Camshaft duration (@.050 in) :211 degree intake / 230 degree exhaust
Initial timing is at 8-9 degrees BTDC
Edelbrock RPM fuel pump
Mr Gasket Spreadbore to Squarebore adapter
The Problem
The car idles nicely with Idle screws about 4,5 turns out. If they are less than 3 turns the engine dies. If I rev the engine at Idle in park before it's completely warmed up, the response is crisp and no bog. When driving even the slightest throttle makes it bog. It doesnt go away up through the rpms. The only situation it doesn't bog is when applying a feather's weight to the pedal. But then it's probably drawing mostly from the idle circuit?
At WOT throttle it still bogs, but slightly less than at part throttle. Tried to adjust the the APT. It was actually all the way down after the rebuild. Then I set it 3,5turns up, then 4,5 and it seemed to improve a bit, but really hard to tell. Overall the engine feels choked. Also tried to physically block off the secondary flaps, but that seemed to worsen the problem.
The engine has been running hot during the test drives. Goes up to 220F and stays there. I have a suspicion that the gauge reading is off, but for now I assume it is correct. If I rev the engine again in park after a drive, the response is really slow, like 1 second after the throttle is twisted.
Some comments that might be relevant:
- the carb has been turned upside down after it was reassembled (goofball friend was visiting)
- when reving in park I observed the secondary flaps opening slightly
- I've got and external filter in addition to the internal fuel filter
Any suggestions on the issue?
Kjetil:
By the way, I also noticed fuel around the edge of the air horn gasket. Could leaks here cause the problems? I did sand the underside of the horn when rebuilding the carb, and used the thickest gasket in the HP kit.
429bbf:
if i had to guess id say your acc pump is sticking. if you shut it off with it warm and look down inside is it getting any pump shot. could have pulled the cup off . rare with chiffs stuff but it happened to me with a napa kit in less than 20 minutes. let us know what you find.
Cliff Ruggles:
Did you set the APT using our "tip-in" procedure?
Did you verify accl pump shot with any throttle movement right off idle?.....Cliff
Kjetil:
--- Quote from: Cliff Ruggles on September 10, 2013, 05:31:15 AM ---Did you set the APT using our "tip-in" procedure?
Did you verify accl pump shot with any throttle movement right off idle?.....Cliff
--- End quote ---
Thanks for the replies.
I didn't do the complete tip in. Reved it up to over 2000rpm and locked it with the screw. Then I held my hand over the top to see if the RPM increased, which it did not. I was a little worried about the temperature at this point, so I aborted the tip-in without pulling a vacuum hose.
Regarding accelerator pump shot it is a big squirt with a quick movement, and almost a solid beam with a slow movement. The latter also seems to go all over the place, but mostly into the barrels. I'm afraid I oversized the holes here. But could the allround bog be caused by the pump?
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