Electric Fuel Pump with a Pressure Regulator on Mikuni SBN Carbs

[#ZERO]

Has anyone ever tried hooking up an electric fuel lift pump inside the fuel tank with a micro externally adjustable fuel pressure regulator on Mikuni carbs set to about 6 psi?

I'm thinking that this idea would work considering the carb's pop-off pressure is high enough to overcome the fuel pressure and the fact that the SBN carburetor still uses manifold pressure along with air velocity to adjust the fuel mixture.

If you've ever hooked up a fuel pressure gauge between a normal Mikuni fuel pump and restrictor, you'll notice that the pressure gauge fluctuates between 2.5 - 3.5 psi at idle to 4.0 - 5.0 psi at higher rpm. Also, it takes a while for the pressure to build up and can fluctuate erratically at idle on some engines.

An electric fuel pump would always maintain a fixed pressure with FPR for more precise fuel tuning, with the correct jetting and without the instability problems associated with mechanical fuel pumps.

They're a few different small pumps ranging from $20.00 up to $50.00 that draw low amperage and would be suitable for in-tank installations.

 

[Goose]

It is def worth giving it some testing i think a constant fuel pressure would be more responsive and alot easier to tune

 

[#ZERO]

I'm thinking it might be a perfect freestyle mod for extra bottom end performance and crisper throttle response.

The fuel consumption should be about the same but the jetting might change a bit especially in the pilot circuit since the pressures going to be bit higher in the lower rpm range.

The more signal you have to the carburetor's venturi makes tuning more precise and the fuel delivery would be more stable without the need for pulse line fittings.

It might also eliminate having to use a fuel primmer when staring the engines cold or after sitting a while and it could be switched on with the lanyard connection or a manual rotary switch.

 

[eel]

I have been using elec pumps on runabouts for years.

You generally don't need a reg. Just return jet it so you have the desired pressure at WOT. I know, it will make too much pressure down low, I hear you say. Run a spring size up than usual and it will run killer.

Use a pump that makes around 6psi.

we use holley black pumps wich are probably overkill on a standup.

 

[Goose]

I did a mod to a 44 once that picked up 20% more fuel signal and about 4%increase on airflow without changing the venturi size. it was a very nice crisp carb and it started in about 4cranks thrue 5ft of fuel line on a bone dry carb. I think a fuel injection with a high speed bypass is the ticket if you can get it setup with multiple injection points

 

[#ZERO]

A restrictor in the return line would probably work fine for an external electric pump that only puts out around 5 to 7 psi.

Those black Holley pumps weigh quite a bit and the in-tank fuel pumps are extremely small and use little current. They are very light weight and are made out of aluminum with plastic impellers.

The in-tank lift pumps supply a bit more pressure and would require an external regulator to function correctly.

They can be mounted with ease inside the fuel tank under the black pipe filler tube touching the bottom of the fuel tank with a pre-filter screen attached.

The ultimate setup would be electronic fuel injection for sure.

 

[Goose]

whoes elec setup is that?I been thinking abotu a mechanical fuel injection setup for awile with 2 injectors in each cyl one in the cases and one in the boost port.run a belt drive pump off the coupler with a barrel valve and a high speed by pass to regulate the fuel pressure when the motor is turning higher rpms.
sorry to get off subject are you gonna give the elec pump a try?when you go to set the fuel pressure id have it at a decent idle and make shure it doesnt climb higher than you want when you rev the motor

 

[#ZERO]

I think that fuel injection setup was posted by waxhead a while back.

The MDR setups only work well at one particular load level, and one particular rpm. The fuel delivery curve is strictly rpm based (driven by a fuel pump at the crankshaft), and allows the owner to make various range adjustments via a series of adjuster screws and pop off valves.

Electronic fuel injection would be the ultimate setup because it can operate at many different parameters with multiple input signals.

 

[Foximus]

Hrmm... seems like a lot of effort in making it fit and wiring it with a waterproof switch.

I just run dual external pumps, both on separate fuel lines, then couple the return line and run a mikuni jet as a restrictor and an inline fuel pressure gauge and I meter it to 6 psi.... Works good enough.

 

[kevbo]

A air seperator would have more value to a freestyler than an electric fuel pump. Those can be filled by a high volume Mikuni pulse pump. Try your electric pump and see how it works out, I would use a relief valve instead of a regulator because they react instantly to flow changes and air bubbles.

 

[#ZERO]

Hrmm... seems like a lot of effort in making it fit and wiring it with a waterproof switch.

I just run dual external pumps, both on separate fuel lines, then couple the return line and run a mikuni jet as a restrictor and an inline fuel pressure gauge and I meter it to 6 psi.... Works good enough.

How hard was it to wire your bilge pump switch?

That would work but why would you need two electric pumps, most external pumps that weigh too much anyway.

A air seperator would have more value to a freestyler than an electric fuel pump. Those can be filled by a high volume Mikuni pulse pump. Try your electric pump and see how it works out, I would use a relief valve instead of a regulator because they react instantly to flow changes and air bubbles.

I like your idea of having a fuel rail with a relief valve on the end but where do you find a 5 to 6psi valve?

I'm not sure the adjustable ones go down that far because most were designed for fuel injection systems.

 

[Foximus]

i have 2 keihen externals, not two electric externals.

 

[kevbo]

I was thinking that one of those valves they sell for noisy waterboxes would be ideal. It could be mounted inside the tank where it wouldnt matter if it leaked. An accumulator with a built in relief and air seperator is the best thing that I could come up with. I just never finished that project. Instead I made a simple air seperator that worked better than I expected. I can run the tank bone dry in the roughest water without any fuel interuption.