06-11-2019, 12:56 PM
(This post was last modified: 06-11-2019, 12:58 PM by Bob Kneale.)
The cause of the dripping carb problem can possibly be traced to higher fuel pressure from the new pump.To a large extent, the fuel pressure depends on the strength of the spring below the diaphragm. The needle valve in the float chamber is doing its best to regulate the fuel flow but is being forced to admit more petrol until the float has the extra buoyancy to force the needle shut.Probably the easiest way to solve the problem would be to replace the new spring with one from the original type 'T' pump. I've done this before and it has solved the problem, but I've only done it once and I may have been lucky..... The basic physics of the problem must be right however.
The number stamped on the pump arm is usually 4079, which works on my engines. The bottom half containing the diaphragm is the same for both type T and U pumps, but make sure the flange mounting is the same - I was caught out by this, and only found out when I came to fit the pump. The type U pump is a better device if you're not too bothered about absolute oriiginality because the one way valves are much more reliable.
Hope this advice/diatribe is of help.
Bob
The number stamped on the pump arm is usually 4079, which works on my engines. The bottom half containing the diaphragm is the same for both type T and U pumps, but make sure the flange mounting is the same - I was caught out by this, and only found out when I came to fit the pump. The type U pump is a better device if you're not too bothered about absolute oriiginality because the one way valves are much more reliable.
Hope this advice/diatribe is of help.
Bob