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Could be a few things wrong Adam but firstly, you'll need to get hold of a fuel pressure gauge and tee it in to the fuel outlet from the regulator that feeds the carb and check that the fuel pressure at idle is 3-4 psi. If its too high (as I suspect your friends is) then it can overpressurise the needle valve in the float chamber which controls the level of fuel in the bowl of the carb itself leading to what you describe.
If you want to check that the needle valve itself is not at fault, one way of checking if the valve is not seating is to take the dashpot off (with needle still attached) and look down into the 'bridge' of the carb where the jet hole is.
Next, wire a 12v feed to the fuel pump that comes on when you turn the ignition on but dont crank the engine, keep it stationary. If you see fuel pissing up out of the jet then the needle valve is not seating as either a) the needle valve is defective and needs replacing or b) the float is defective and is not acting as it should to close the needle valve or lastly c) the needle valve and float are both fine but the float height has been incorrectly set and needs properly setting up. Either way, it'll need the carb off and good old inspection and re-set of the needle and float.
If fuel pressure is too high, it's not unheard of for the float to be split due to overpressure. This then allows the float to fill with fuel.
The plenum 'signal' line to the pressure regulator is there to allow the regulator to sense boost in the plenum. The design of the regulator allows it to deliver fuel pressure constantly to the carb at 3-4 psi ABOVE the boost pressure (or whatever you have it set to - hence the need to know what it is with a gauge and tee piece). The regulator is easy to adjust, just take the top cover cap off to get access to the brass screw, slacken off the locknut holding the screw, turn the screw anticlockwise to lower the fuel pressure, clockwise to increase it until the gauge reads 3-4 psi then holding the screw still, nip the locknut back up and replace the top cover nut.
If the regulator didnt have this 'rising rate' ahead of boost, then the boost pressure would send all the fuel back to the pump back to the tank and the engine would seriously lean off as soon as boost came on.
Another thing to check is that the gasket between the plenum and carb has the small signal hole cut in it to take the upstream pressure from the intake to the base of the float chamber. This is essential otherwise you have to incorporate the 'Tee piece trick' - look it up by searching if you need more info. I dont think this is the source of your overfuelling tho.
Lastly, have you blown through your fuel return back to the tank ? Is there a restriction ? You should be able to take it off the regulator and blow it through with pressure from your mouth until your mate hears the hissing sound in your tank, assuming you havent put the return line in too low in the tank - it should be nice and high, say in the neck of the tank, pointing down to the fuel within the tank. If you cant blow it through, check it out, it needs to be as free as possible. The size of this pipe is important, it needs to be at least 8mm internal bore, 10 mm preferably.
I suspect the carb float needle valve is worn in its seat or the float is buggered. Either way, its a cheap fix. If you do go for a new needle valve, make sure you get a Viton tipped needle.
Come back after youv'e done those checks.
Richard.
Edited by turbominivanman on 4th Apr, 2011.
Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u
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