EFI conversion - External/Internal fuel pump

Eszterle · Jan 19, 2011

Hi!

I'm thinking about converting my FS650 to EFI and got a little bit stuck at one point ...

I'm a bit unsure about the solution regarding the fuel pump. There are 2 ways which I would take into account ...

1. External pump
An external inline pump just connected to the fuel tank on one side and connected to the EFI and the pressure regulator on the other side with the drain back into the normal fuel tank. This would be a really nice solution since it's P&P. But I'm a bit unsure about the fuel pump sucking air. What do you think about that? Do the inline pumps have a small buffer tank or is the game over as soon as it sucked a little air?

2. Internal pump in a surge tank
This solution would include 2 pumps (low&high pressure) and a surge tank. It's not that P&P and more complicated. Also heavier and so on. BUT it would insure constant fuel supply at all times.

What do you think about that?

Kind regards

berger · Jan 19, 2011

Why would the pump suck air?

Eszterle · Jan 20, 2011

berger said:
Why would the pump suck air?

Because my tank isn't always filled to the top and my Berg isn't always in an upright position ...

Maybe I'll just try it out the first way and if the air becomes a problem I can still install a surge tank. But maybe someone already has some experience on that ...

Regards

Davo · Jan 20, 2011

Send user Dr_C a PM. He is setting up an EFI road racing bike and would have to considered fuel surge as he would melt a piston for sure if he has not.

I have no experience with EFI on a bike but would think about a gravity fed surge tank under the main fuel tank if it would fit. You would need a feed from the bottom of the fuel tank to the top of the surge tank and an air return line from the top of the surge tank to the top of the fuel tank.
I have only tinkered with boats and cars where I always use a Holley Blue low pressure fuel pump to feed surge tanks. But a Holley Blue would be overkill on a bike.

Eszterle · Jan 22, 2011

Hey!

I'm already writing with him for some time now but unfortunately he didn't answer on my last mail about that problem till now ...

Why would I melt a piston through fuel surge? The engine just doesn't get fuel for a short period. When switching the fuel off while running down a hill (What almost all new cars do ...) or when my tank is empty and the engine is stalling the pistons also don't melt. As long as it's no 2-stroke it shouldn't be a problem?

However, I'm thinking about solving it with a small surge tank. Probably as you suggested fed through gravity. But finding a small surge tank isn't that easy ...

Bosch offers a small fuel filter which could work. I already read about someone who converted a Honda or something 650 with such a "surge tank fuel filter". But I'm a bit unsure if it's big enough ... ?

Regards

RedRockRider · Jan 23, 2011

Are you using the microsquirt setup? Check out their info: http://www.microsquirt.info/indexright.htm

Eszterle · Jan 23, 2011

Hey!

Thanks! But I already know this site (and maaaany others from MS/µS).

There is no info on this site about fueling. There is some information on some sites but because the MS thing is universal it is mounted on cars and bikes and stuff and the guys don't know where it will be mounted so they can just suggest to fit it the one way, without a surge tank, or the other way. There is no exact information about how to fit it to a bike. Besides that some bikes would probably need a surge tank and others won't.

But it looks like there's no one able to help me here.

But no problem ... I'll find a way.

One question ... Does the FS570 have a surge tank?

Regards

bushmechanic · Jan 24, 2011

the busa hillclimber had some issues sucking air, will find out exactly what

I think the gist of it was to mount the pump externally and well below the bottom of the tank (as low as practically possible on the bike) with a large diam feeder tube, gravity keeps the tube full and the tube should be enough for a surge "tank".

Davo · Jan 24, 2011

Eszterle said:
Hey!
Why would I melt a piston through fuel surge? The engine just doesn't get fuel for a short period. When switching the fuel off while running down a hill (What almost all new cars do ...) or when my tank is empty and the engine is stalling the pistons also don't melt. As long as it's no 2-stroke it shouldn't be a problem?

If you were road racing the bike and were going down a long straight full noise with low fuel the fuel would be slooshing around in the tank when you are changing gears or hitting bumps etc... When air gets in the fuel line the pump cavitates and fuel pressure lowers. The engine runs lean with low fuel pressure, and then bad things happen. If your just trail riding it wouldn't melt a piston. If you have a surge tank and it runs out of petrol the pressure "usually" drops to zero real quick and the bike stops. It's that sloshing around in the tank and getting half air half fuel that causes trouble.

Eszterle said:
But finding a small surge tank isn't that easy ...

I just make them. Buy a bit of aluminum tube and cut out aluminium plate for the top and bottom of the tube. Buy 4 weld on fittings, then get someone to TIG weld it together. I use Speedflow #6 weld on fittings.

Eszterle said:
One question ... Does the FS570 have a surge tank?

It does not have an external surge tank and I am not sure if it has some kind of design inherent in the tank that holds petrol near the internally mounted EFI fuel pump. I have never had my tank off. Someone else maybe able to comment.

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EFI conversion - External/Internal fuel pump

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