DFI Fuel Injection and Fuel Pumps

Hi MotoKa
I have been doing the same myself.
I put an adjustable pressure regulator and gauge in the line after the pump , so I could see what was going on.
I had replaced the original jec fuel pump with a walbro, however its too high capacity or volume for the new vacuum petcock or fuel valve, as it pumps 150 litres per hour.
I was getting bubbles in the return line.
So I moved the clear plastic filter to the pressure side of the pump and could still see bubbles.
Then I moved the fuel pickup to a jerry can and it was finally happy
Also check the return check valve as mine was blocked when I got it, and the tank was rusty.
I replaced the adjustable pressure gauge, because its bulky, with one very similar to the original from just commodores in australia.
A commodore is an aussie GM car . The VK model was built at the same time as the dfi and ran the 38 psi injectors. It also has the vacuum port that drops the pressure 2 psi when at idle. That's my understanding anyway but happy to be corrected.
My final issue ( hopefully after a year or more) is I don't want to be riding around nursing a jerry can.
Been looking hard for another pump that is a lot slower than the walbro.
I found a 50 lph bosch , but its an in tank version and I want an external.
Many pumps don't disclose what the volume is. Anyway I just bought an inline pump from china for a moto guzzi and try that.$80
I will rig up the old pump and just check what volume is does pump, and check the new one when I get it next week.
Have a fire extinguisher handy.
These bikes can also lose compression if they sit too long.
Good luck
 

Hello Hoganter,
Which Walbro pump were you replacing?
Bill

MotorKa wrote:

Hi everyone,
I’m having trouble finding the service manual — I can’t see it on the homepage at all. Could someone please point me to the correct link? Ideally I’m after the DFI (EFI) supplement for the Z1300/ZN1300. I’m troubleshooting an issue and need to verify fuel rail pressures and related test procedures.
Many thanks!

 This thread about fuel pumps may be helpful to you.

DO I NEED A FUEL PUMP?

 

Hi Bill
Its a Walbro 393
thanks

hoganter wrote:

Hi Bill
Its a Walbro 393
thanks
 

Hi Hoganter,
Why isn't the WalBro393 the right pump? The chart on their website seems to say that at 35 psi the 393 will flow 35 GPH.
Thanks
Bill/KZQ

Hi Bill

I measured the walbro through a regulator which I think is 38 psi and got 4.8 litres in 2 minutes. 4.8 x 30 = 144 lph /3.78541 = 38.04 US gallons per hour

I measured the original Jec through the same regulator and achieved 2.6 litres in 2 minutes. 2.6 x 30 = 78 lph/ 3.78541 = 20.6 US gallons per hour.

So my original pump is about half the capacity of the walbro.

I am going to put the Jec back in because the new fuel petcock I bought is too restrictive for the faster walbro pump and I get bubbles in the fuel rail which causes it to run poorly.  

Also the Jec looks like it has a check valve in it and I did not have one on the walbro ( not sure if it makes a difference)?

The original petcock may not have that issue but you need pliers to operate it, so I retired it.
The new one is vac operated but does have a prime setting. I was restricted for choice as I needed a 44mm to fit. 

I have ordered a new moto guzzi pump but it has not arrived yet.
It should be all good 
Cheers