What does the second screw on a turbo pump do?

[dansvan]

Just curious.

 

[Exekiel69]

You meant the one in the back? That one I believe changes the way the IP injects the fuel, sooner or later on the acceleration.

 

[Headerpower]

The one on the back that runs in at 90* is the spring tension on the governor linkage to the metering valve. After having one apart, it appears to me that winding that in would increase the spring tension, resulting in fuel flow rate increasing later as you get closer to WOT. The second screw you are refering , more to the drivers side back of the pump, and installed at an angle is a stop screw for the metering valve arm. Backing it out some opens up the metering valve allowing more fuel into the injector pistons- there by providing an easy adjustment option if you were adding a turbo to a N/A tuck, or just wanted to buy one production line of pumps that could be used easily on a N/A or turbo truck. The screw located under the plate on the passanger side, as it is wound in opens up a leaf spring that allows the plunger pistons to "open" up more - pushing more fuel, but is not as easy to do and spills fuel everywhere!

 

[f-two-fiddy]

The one on the rear is a low speed fuel limiter. It reduces fuel when you floor it at low RPM's. Thus reducing the black cloud that appears without it.

 

[Optikalillushun]

Anyone play with any of these screws with sucess?

 

[aaklingler]

I went out a turn or 2 on the screw that goes straight in the back and seemed to give a little more fuel. I turned the internal screw in 2 flats and that gives me plenty of fuel on an na.

 

[f-two-fiddy]

The Low Speed Fuel Limiter does'nt do much. Just waste's fuel, and produces black smoke(unburned fuel).

Untill the turbo spools, at around 1500 rpms, there's no need for any extra fuel.