quote:
Originally posted by B.P.Bird
Gus,
... For what it's worth I find that the needle valve on the 48 IDA is the culprit in most flooding problems. ......
For your amusement.
I had had the occasion to bench tested used 1960s, new old stock 1960s, and 1970s and newer genuine O.E. IDA needle valves. Simple test, invert the assembly (gravity only working on parts), and do a leak down test. The results were interesting.
Modern (late 1970s to circa 2006 made selection) valves. So far I have not found a modern one that seals. I tested about six four carburetor systems worth. I haven't found one that will hold even a couple of inches of water column pressure. I took some to a real nice microscope for examination and found the internal surfaces rough (rough tool marks) and the passage bores exhibited clear evidence that the boring tool chattered and in most cases left the bore slightly oblong. On the worst one I had to apply approximately 8 pounds in dead weight to make the rubber needle tip conform to the oblong hole. Once I did that it subsequently stuck there. See sketch below.
1960s parts, even used valves once used on a race Cobra long ago. Sealed tight every time. In my last test session I applied 20 psig compressed air and let the air pressure 'lift' the needle. I shut off the air supply and checked leak down. My gage (uncalibrated I am afraid but instructive none the less) showed the pressure bleeding off until a point the needle would not lift any longer. The valves tested stopped bleeding off between roughly 8 and 14 psig. I repeated the test several times dry and several times wet with a light lubricant. Adding a wetting agent didn't significantly change the bleed down results. I examined some of these used and new old stock valves under the microscope also. The bores in the 1960s valves were very smooth walled and the needle contact interfaces appeared very true to the needle tips.
My conclusion was that a lot of modern troubles with the IDA series in fuel control is due to the apparent low amount of care taken in the manufacture of the modern needle valves. (Note: I have run up against a few problems like this on needle valves and power valves for modern made Holley brand replacement parts for Ford applications that I have worked on. The issues are frequent enough that every valve gets bench tested prior to final reassembly. I do cull out and discard brand new service parts from time to time.)
