SBC stock 350 in a 72 Monte Carlo. Idles great and pulls a steady 15 inches of vacuum, no misses. Drives perfect until you accellerate hard and then it back fires through the carb (QuadraJet). My thoughts are possible bad valve spring, flat lobe on the camshaft, ignition problem? Anything else possible and your thoughts are appreciated as always.
SBC stock 350 in a 72 Monte Carlo. Idles great and pulls a steady 15 inches of vacuum, no misses. Drives perfect until you accellerate hard and then it back fires through the carb (QuadraJet). My thoughts are possible bad valve spring, flat lobe on the camshaft, ignition problem? Anything else possible and your thoughts are appreciated as always.
A steady vacuum reading would not be indicative of a bad valve spring, or flat lobe, quite the contrary a steady needle indicates things are pretty fine.
The first place I suggest is the accelerating pump. If it immediately snaps back thru the carb, the pump shot is too little and or too late. Q jet pumps tend to leak past the rubber piston as they age giving a less and later shot.
If it snaps back when reaching WOT chances are this is the mixture dropping lean possibilities are:
1) Not getting onto the power enrichment part of the needle:
- Power piston hanging up
- Wear in the linkage of the mixture needles
2) Float level too low
3) Fuel pump wearing out and can't keep up to WOT fuel flow requirements
4) Plugged filter or failing fuel lines.
Bogie
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