MSefi.com read only forum (Jan.15,2018)

I'm currently in a re-design process for my motorcycle fuel-only project. The first time I built it I had no experience and made a few mistakes (putting components in what turned out to be stupid places), the main one was that I put the fuel pump too high in relation to the fuel tank petcock (that item caused real problems). There's just so little space available in the little motorcycle to shoe-horn in all the elements of a fuel injection system and I really didn't know what I was doing. I feel that now I'm making much better decisions as to where to locate everything.

In my re-design I've placed the fuel pump way down low in the bike's frame to make it the lowest part of my fuel system. I've also relocated the MAP sensor, the FIDLE, the Wideband O2 controller, two of the relays, the fuel filter and the fuel pressure regulator. All items are now in places that utilize space better and increase my ability to service the bike.

So here's my fuel system design question:

In a motorcycle type of fuel injection system where the fuel rail is a dead-end (there's no re-circulation of the fuel, the only place for it to go is out through the injectors), does it matter in what order the fuel filter and the fuel pressure regulator are placed?

I could easily put it together in this order: fuel pump to fuel pressure regulator to fuel filter to fuel rail.

Or just as easily in this order: fuel pump to fuel filter to fuel pressure regulator to fuel rail.

Does it make any difference to have it either way?

(The bike also has a simple low-pressure fuel filter on the supply line from the tank petcock to the fuel pump.)

I don't think it matters a huge deal, I personally would put the filter before the regulator to prevent crud from entering the reg.

Usually the Regulator comes after the fuel rail - assuming a fuel return.

LeslieTroyer wrote:Usually the Regulator comes after the fuel rail - assuming a fuel return.

No return fuel from the rail on this system.

Most motorcycle throttle body assemblies are designed with a "blind" or "dead end" fuel rail. The fuel rail only has one fitting, and that's the input fitting. There is no "take off" line at the other end of the fuel rail (beyond which I understand you would normally place the regulator in a car-type system).

It was because I'm working with the motorcycle style "dead end" fuel rail that I was asking this design question. I'm also working within a very limited space (it's a very small motorcycle, Kawasaki EX-250). To be perfectly honest I'm finding that it would be easier and neater for me to put it together as follows: fuel pump to fuel pressure regulator to fuel filter to fuel rail. Just hoping there's not some sort of flaw hidden in doing it that way.

As I said on the original post, I've also got a simple, non-pressurized fuel filter on the input line from the tank's petcock to the fuel pump. I was thinking this filter would protect the pump and the regulator and the high pressure fuel filter would protect the injectors.

Dito on the challenge to fit items on a bike I have moved everything you mention (plus a few more) on my "phase 2" session last year, and now will engage with another round with "phase 3" in what I hope is the final arrangement.
My bike may be larger than yours (R100RT BMW which is 1 liter), but with the super well designed fairing, there is not much room to tango.
I would concur with what others have offered, in that the only factor with the filter location would be keeping crud out of the regulator. If you have the pre filter in place, that shouldn't be much of a concern with your desired method.

It's important that your pressure regulator is designed for controlling downstream pressure for your application. Most regulators for fuel injection systems are for use with a fuel return line and therefore, they are designed for controlling upstream pressure. Anyway, I agree with others here that the filter should be upstream of the regulator.

Kompressor wrote:Dito on the challenge to fit items on a bike I have moved everything you mention (plus a few more) on my "phase 2" session last year, and now will engage with another round with "phase 3" in what I hope is the final arrangement.
My bike may be larger than yours (R100RT BMW which is 1 liter), but with the super well designed fairing, there is not much room to tango.
I would concur with what others have offered, in that the only factor with the filter location would be keeping crud out of the regulator. If you have the pre filter in place, that shouldn't be much of a concern with your desired method.

Thanks for the response. It's scary to hear you're headed into your third re-arranging of components. I was hoping to get it right in two tries (we'll see how that goes).

I guess the real question in my mind is, "just how delicate is the pressure regulator?" I'm inclined to believe that the feed-line pre-filter is all the protection against crud or particulate the pressure regulator would need. I always figured that the injectors, with their tiny little openings, were the main concern of the high pressure filter.

It's important that your pressure regulator is designed for controlling downstream pressure for your application. Most regulators for fuel injection systems are for use with a fuel return line and therefore, they are designed for controlling upstream pressure. Anyway, I agree with others here that the filter should be upstream of the regulator.

No worries on that issue. I'm using the fuel pump and pressure regulator from a Suzuki LT-R450 Quadracer. On the Quadracer the fuel pump feeds into the pressure regulator which feeds directly into the "dead-end" fuel rail. I have it installed on my project bike in the same order as on the OEM product.

The part of the Quadracer system I couldn't use in my project was it's large, complex combination fuel filter and fuel swirl pot component. That's why I've got questions about fuel filters and their placement.