Do I need a fuel pump ?

Thanks Kawboy ! I got the book and read it, good information. Since then I've purchased a couple of pumps that weren't adequate. Currently I've fitted the Walbro 393. The first try was a failure. The pump came up to pressure but no fuel was being delivered. I pulled the injectors and cycled them as described in the service manual. I finally got everything together yesterday and once the air was purged the bike started and ran despite the pressure regulator, which had previously been regulating in the mid 30s, now letting 85 pounds of pressure through.
Oh Well, It did start and run. I've still more to do.
Bill

OOPS! the 85 lbs of fuel pressure was caused by my having kinked the vent hose from the regulator as I lowered the tank into position. I rerouted the hose and the pressure is now 36 PSI. The bike runs, but poorly. I can see air bubbles in the fuel filter. I'm thinking that either the regulator is venting so much fuel that it's foaming the fuel in the tank or the pump has so much suction that it's causing cavitation at the petcock.
I've thought I could try throttling down the flow with a ball valve between the pump and the fuel rail. Or I could reduce the operating voltage to the pump with the addition of an inline .5 ohm ballast resistor.
The ballast resistor and ball valve arrived yesterday. Ballast resistor first, ball valve second.  I'll get to it later today.
Thanks
Bill

No need for the ball valve.
I started the bike with the Walbro 393 at full voltage and noted the agitation of the bubbles in the fuel filter. The pressure gauge shows 36 PSI.  Bliping the throttle revealed quite a bog off idle.
I fitted the half ohm resistor to the fuel pump and restarted the bike. The pressure gauge still shows 36 PSI and the agitation in the fuel filter is noticeably reduced. The off idle bog seems less but, of course, the engine is warmer.
When I previously saw 85 PSI I had thought the regulator was at fault only to find that I'd kinked the vent line. 85 PSI is the dead head pressure for this pump at 12Volts. This time with the vent line from the regulator clamped off and the half ohm resistor in line, I found the dead head pressure to be 60 PSI.
I'm going to go to a three quarter ohm resistor. I think I can get to 45 PSI, if the pump will run at 6 volts.
Bet it will.
Bill

Just some thoughts Bill.
Walbro specs out the GSL393 pump at 155 LPH and able to support up to 405 HP. Just based on the 405 HP spec the pump is too big UNLESS you have a regulator capable of flowing 155 LPH at a dead head.

It doesn't matter what the dead head pressure of the pump is provided the regulator can handle the flow rate. The regulator gets set to fuel rail pressure and any excess pressure gets returned to tank.

If your pump / regulator will hold rail pressure at 43 psi, then your problem is not a pump regulator issue, leaving input signal or output signal / injector mechanical issue assuming the the computer program hasn't been tampered with. My control techs back at the plant would always tell me that my issues were not computer related and likely a mechanical to electronic interface on the input side, or an electronic to mechanical interface on the output side.
If your fuel pressure on the rail is 43 psi and your injector are all responding to the input voltage, then likely your off idle bog  is a problem with the variable resistor ( throttle position sensor) adjustment. 

I would test the TPS and insure that there's no flat spot or open circuit in the resistor, then adjust as per manual.

The other thing that comes into play is the engine temperature sensor which tells the computer that the engine is either up to temp or cold. When cold, the fuel map is richened up, although there's also the manual choke butterflies in the throttle bodies. Those manual butterflies are so contravening to any standard fuel injection system I've ever seen. When I finally get around to working on mine and installing the Megasquirt computer, I'll be removing those butterflies and mapping the fuel signals to richen up the fuel on a cold engine.

Hope this helps
KB

Thanks Kawboy,
I'm just happy I found a way to slow down the Walbro pump. I'm going to take it another step down later this morning. My hope is to get it to dead head nearer to the specified operating pressure. As was the case with the original pump. There's a reference in that book you recommended that suggests that too much flow in the return line is not desirable.
I've got that special tool to adjust the TPS. It'd be just too cool if it's capable of smoothing that lag off idle because while I still have the original air box, the bike is currently sporting pod air filters.
While I'm thrilled that I've gotten this system running, I'm mindful that the next part that falters will probably be it's end. I may be in the market for a mega squirt system before you are.
This bike is/was a Voyager and as such it was slathered with additional systems such as a motor adjusted head light and an air compressor to adjust the suspension on the fly. I sussed out and capped off all the extraneous wiring. I'd love to just remove all of it. Presently it's just tucked up into what's left of the fairing.
Regards
Bill
Later: I installed the three quarter ohm resistor in line with the fuel pump. The dead head pressure is now 50 PSI and the system pressure is still 36 PSI. My pressure regulator is the stock regulator however it's been modified to be adjustable. I'll play with the adjustment to see if I can get it down to 33PSI.
I'm satisfied with this pump installation, for now.  It's time to move on to the TPS adjustment.
Bill