OK, I just purchased an '83 Z28 (LG4). The car is a converted 5spd, 305 LG4 with stock quadrajet 4 bbl, "Edelbrock performer cam, intake manifold and valve springs", Heads were rebuilt with new valve seals.

The car idles nice and has power. Problem is when you get on it (approx 4000-4500 rpms), it starts to bog down. When this happens a strong smell also comes out of the exhaust. The guy I purchased it from told me he felt confident that a new carb would fix this problem.

From what I'm reading on this message board the Quadrajet is a pretty decient carb. It's it possible the existing carb needs a rebuild or secondary rod & hanger change-out or maybe just a tune? Any advice would be great.

Thanks!

 

Yep, you're definately on the right track.
So if you punch it at 3000RPM, it goes just fine, but at around 4000RPM it bogs down? Not as soon as you thump the gas pedal down?

If you start from a dead stop and pin your foot to the carpet, it'll go just fine from idle up? Does it start to bog by 4000RPM in 3rd gear?

If it bogs from first stab of the gas at around 3000RPM sorta thing, adjust your secondary air valve tension. Check the main page of TGO here, look at a tech article about "Air valve tension". It's a really really really common problem with these carbs.

If its the second case I mentioned there, then it's most likely the fuel pump, or a plugged fuel filter. It's a $2.50 filter, so if theres any doubt in your mind, replace it.

 

Air cleaner. The stock LG4 single snorkel is a restrictive piece of garbage.

Exhaust. The stock LG4 system is a restrictive piece of garbage.

Timing. Make sure it is set right. You can usually advance the base above the stock zero degrees - try advancing in 2 degree increments and see what happens. But, it won't help high-RPM much as long as the stock air cleaner and exhaust are in place.

 

My 1st thought is secondary AV tension. Read the tech article carefully. Getting it just right takes a lot of adjusting and testing. An easy mistake is to make it too loose. Revving the motor in the driveway is not going to tell you anything. You have to test it on the road under load. If you can feel the secondaries kick in abruptly, it's prolly too loose.
Also, a problem I had was that the AV plates were getting caught up on the top plate of the carb. This was easily solved by cutting a paperclip and screwing it under one of the rear airhorn screws. I bent it down just enough to prevent the plates from fully closing. Instantly cured a WOT bog that I had.
I agree with said advice about Air cleaner and/or exhaust restrictions, but these generally won't create a "bog" as much as they cause the acceleration to to fall flat on it's face.
Opening the air intake should take priority over the exhaust. Not only because it's considerably cheaper, but also cuz a better exh. can't help much if it doesn't have more to exhale.
Remove the stupid silencer ring from the AC that's surrounding the carb. Also remove the plate that is 1" from the AC's opening from the snorkel.
Get yourself a K&N air filter, and if you're really serious gut out the thermac valve from the AC's inlet, or chop the inlet off before the valve and run some dryer duct to the bottom of the engine bay for some tasty colder air.
Unfortunate owners of Auto Tranny's will see quite a gain from this. The 305 will pull much further on the tach before shifting.