I purchased an Edelbrock 600 cfm Performer carb, number 1406 brand new. This is sitting on my 350 Chevy engine in my 1969 Nova. Ever since it has had a stumbling problem. The stumbling problem initially started in the mid RPM’s when getting on it while on the interstate. I could take off from a dead stop just fine, with smooth acceleration, but about the mid rpm of 3500 or so, it began to develop a hiccup. The engine would occasionally sputter and spit. Then the stumbling became more noticeable, to where if I mat the pedal from a dead stop, it sputters and feels like it’s only running on 7 cylinders. I have verified by the water trick on the headers that all 8 cylinders are firing. So far I have set the timing to 12 advanced BTDC, have the mechanical set to 24 degrees advanced for a total of 36 degrees all in at 3000 rpm. I do have the vacuum advance hooked up on the full vacuum side. I have a brand new ignition system consisting of a Mallory small body HEI with a Flame Thrower coil and Taylor 8.2 wires running to AC Delco plugs. I have checked for vacuum leaks using a can of carb cleaner and have not found any. I have changed the stock metering rods and springs to a 7037 rod and a pink spring. I also changed the primary jets to a .101 and the secondary jets to a .098 size. (factory this carb had a .098 primary, .095 secondary and yellow spring, with a .075X.047 rod – I set this up to be more like the model 1405 Edelbrock) I also checked the floats and adjusted them to read 1” from the underside of the carb top when hanging down and 7/16” of the carb top when sitting up. Thinking maybe there was some crap in the carb, I disassembled the carb and cleaned out all the nozzles, venturis, etc. with carb cleaner. I did find a piece of aluminum metal shaving in the accelerator pump chamber, but I promptly cleaned it out. I also removed the needles and floats and sprayed carb cleaner in that area too. I have tried different positions of the pump shot adjustment. All in all, I still have a stumble. My Nova has a TH350 with 3.55 gears out back, and I can’t even spin the tires when I mat the pedal, that’s how bad it is. So now I don’t know where else to turn. Any ideas?
Posted on: Mon, 21 Jul 2014 14:27:07 +0000
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