Hey everyone,

Im looking for some trouble shooting help. I recently swapped out my stock intake and carb on my 67 327. Previously the engine was running fine. The original carb was a 750 quadrajet. On the engine now is a vintage edlebrock c3b manifold (precursor to the performer) and a 600 cfm Holley Brawler. Vacuum is at 19-21, timing is at 8 degrees before TDC, and floats are center of the viewing glass. The engine idles great. While under the hood and moving the throttle there can be a slight hiccup or stall in the engine. The engine seems to have a bit of odd vibration. Not like when a spark plug is bad or a motor mount is broken. Seems to me like inconsistent fuel flow. While driving, the engine sputters and stalls. This occurs at initial acceleration, backing up or going forward. I have read that if fuel pressure is not 6-6.5 psi that this could be the problem.

Any input is appreciated

 

have you checked what your FP is?

 

My fuel pressure with the coil wire off is a weak 5.5-6 psi. At idle the needle jumps all over the place. I remembered when I woke up this morning that I did not adjust the fuel bowls at idle. ill have to get on that.

 

Mechanical pumps supply 'volume' of fuel, not pressure. It should pump a quart in 30 seconds at 1000 RPM.
Float level too high, adjust to the bottom of sight hole.
When Q-jet was on, was vacuum steady?
Is compression readings within 10%? If one cylinder is low, squirt oil into cylinder and redo compression. If it goes up, poor ring sealing for this cylinder.
If not, bad valve, as in burnt - has a hole at the valve head to seat.
You could change oil and add a bottle of GM's EOS as it is designed to help sealing.

 

Thank you for the response. volume check, all I know is the fuel gauge in my duel fuel line insert is reading 5.5-6 psi. Previously the vacuum was around 19-21 at 6 degrees before TDC timing. I don't imaging having significant compression loss of a burnt valve since the engine was running great previously.

 

Physics - Pressure is resistance to flow.
The pressure is fluctuating because of the pump being actuated by the camshaft lobe. Otherwise, open fuel line, 2 PSIG
agree with you on running good before
Get an adapter plate and install Q-jet just to see results.
Adjust Holley accel pump linkage for 0.020" clearance
It might need two size larger squirter nozzle, i.e., 25 to 27.