Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Exhaust popping during fast idle when cold.
Tyler73Deville:
73 Cadillac 472 with stock cam and near stock calibrated quadrajet #7043234. Only changes made were made to the jets (2 sizes larger to .070, and long green power piston spring) runs non-ethanol 91 octane. Pulls around 19" vacuum at idle and easily starts even in sub 20 degree weather for it's winter start ups.
Deleted egr and has dual exhaust. Runs great, idles well and has awesome throttle response otherwise (absolutely smokes the rr tire lol)
Has msd 6al running 16 initial, 37 total by 3000 ish
What gets me is running vacuum advance to manifold gets rid of said popping during fast idle on cold starts... likes lots of initial...it's 30 degrees with it connected at idle...maybe she's a bit lean on idle/ transfer slots perhaps? No nozzle drip and goes away a bit when completely warmed up.
Also did the tip in method at higher rpm with the choke and seems cruise metering is spot on.
Thank you.
Tyler73Deville:
Went from the much thicker insulating base gasket on the left, back to the correct one on the right, fixed the issue.. always the small things... thought I'd share...
Shiny:
What effect do you think the gasket had? Glad it went away but I'm curious why...
Cliff Ruggles:
The thickness of the gasket had nothing to do with the improvement.
You are allowing one side of the intake to see the other side. I've found better results going to the first gasket you had in place as far and engine performance was concerned.
As far as the skip or miss in the idle you should be using vacuum advance, but may have to reduce how much it is adding. Most vacuum advance cans add WAY too much timing when we start advancing initial timing.
Is it a factory distributor are an MSD unit?
How much timing does the VA add and are you using it?
Shiny:
Still curious...so the effect of the gasket change was to somehow decrease vacuum signal to the advance unit?
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