Timing or Fuel issue?

yooper12

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Had my 62 Newport 361 engine rebuilt stock and upgraded to 500 cfm 4bbl Edelbrock carb. After the first 100 break in miles I started noticing hesitation and sputtering above 55mph. Runs strong and no issue until highway speeds. Initial timing set at 10 btdc. Can't seem to find a vacuum leak. I have the distributer vacuum advance attached to passenger side carb port. Any help on this one appreciated.
Yoop

62 Newport.jpg
 
Presuming the fuel pump push rod was replaced during the rebuild? That the issues at and above 55mph did not exist before the rebuild? If you put the car in "2" and drive it, does the same thing happen at a lower road speed than in "D"?

What about the distributor point dwell? Is the point gap in spec when the point dwell is in spec? If not, then the breaker cam on the distributor shaft (what the points rubbing block rubs against) is worn and the dwell being flaky might result in a weaker spark. Only cure would be a different distributor or an electronic conversion kit.

How original is the muffler? Kind of sounds like a restriction might be causing a flow issue?

With the new carb, I'd look more toward an ignition issue. As some ignition and fuel issues can act pretty much the same.

Now, as to how it is acting, is the "sputtering" at a steady cruise speed or is it more on slight accelerations? Or part-throttle accelerations where throttle input approaches WOT but not automatic downshift speeds?

Am I giving the carburetor "a pass"? No, as I suspect the metering calibrations are decent for that engine size. If it was very lean, it would not respond as well and end up popping-back as engine load is increased. At those rpms, the main system is running things, with NO input from the idle mixture screws.

The muffler? Might a baffle have come loose and moved such that higher flow rates are compromised? It used to be considered that if such was the case, a rattling in the muffler could be heard if it was hit upon with the car not running, on an overhead lift.

Please keep us posted on your progress.

Just some thoughts,
CBODY67
 
Check gas tank venting. Spark plug gap. Plug wires (too high resistance if using modern wires?). Hope you're using a good break-in oil with lots of zinc.
 
Thanks for the response! I should have mentioned that points have been replaced with pertronix unit. Sputtering happens at stead cruise above 50. Muffler over 30 years old single exhaust. Did not have any issues with 2nd or 1st gear (or reverse). Have new rod/fuel pump. Fuel pressure was 5.5 at start up. I will recheck.
 
My 300L 4spd came with an Edelbrock carb and it ran pretty poorly at highway speeds. Carb was way too lean. Got an original AFB and she ran so much better. Many of those new AFB/AVS carbs are calibrated for economy.
 
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