Gravity Feed, Need The Collective Wisdom A.s.a.p

[V4 Rosso]

So I am going on a trip tomorrow to see the WSBK races at the Nürburgring on sunday. But this evening getting home, my fuel pump died and so did the viffer. Fortunately I was not too far from home and called my brother to bring some of my tools and some fuel line so I could switch to gravity feed. Now there isn't enough time to get a new fuel pump (the dealer did not have one in stock and the breakers was out too) and I have the choise of either sticking with the gravity feed or try to use the (aftermarket) fuel pump of a austin mini. I do not know the capacity and the output pressure of that pump, also it is a lto larger than the vfr pump so possibly won't fit.

What is your opinion, can I stick with gravity feed? I've done some accelleration tests and it looks like I am going to be fine, but what about mileage on a tank of gas, when I get to reserve it looks like the fuel level is not a lot above the float bowls and I don'like suddenly running out of gas in the middle of nowhere.

Please share your experience if you had to deal with the same thing once, thanks.

[Baileyrock]

Bummer, I can't remember which bikes, but I know some models can run fine w/o the pump. Just don't remember which one's, sorry and good luck! :fing02:

[Beck]

Maybe if the carb size and displacement of the mini (850cc - 1000cc??) comes to about the same of what totals for the four carb setup and displacement on the VFR, then you might be in the ball park. It might get messy if the Austin's pump is rated higher. Over pressurizing and flooding of the carbs and possibly having fuel come out of the carb overflow vents. Personally, I'd try to keep safe and opt for the gravity feed if the bike would run that way. You might need to keep the gas topped up most of the way to keep the gravity feed going.

Beck

95 VFR

[SEBSPEED]

Is there a manual download available for your bike here?

The gravity feed topics here have been related to the earlier 80's VF/VFRs, but if you are carbureated you should be ok without it?

Make sure your gas cap is venting properly so you don't create a weak vacuum within the tank, I think this is your only limiting factor!

Make the fuel line from the tank to the carbs as short as possible!

Good luck!

[V4 Rosso]

Maybe if the carb size and displacement of the mini (850cc - 1000cc??) comes to about the same of what totals for the four carb setup and displacement on the VFR, then you might be in the ball park. It might get messy if the Austin's pump is rated higher. Over pressurizing and flooding of the carbs and possibly having fuel come out of the carb overflow vents. Personally, I'd try to keep safe and opt for the gravity feed if the bike would run that way. You might need to keep the gas topped up most of the way to keep the gravity feed going.

That is my concern too, over pressurizing. The mini has a slightly tuned 1300 engine (Cooper S spec) and puts out about the same HP as the VFR. The fuel pump is aftermarket as the original couldn't deliver enough fuel to the engine. But as the gastank in a car is always below the float bowls and the fuel line is a lot longer it will likely be rated somewhat higher both in flow and pressure. I will stick with gravity feed, I replaced the fuel filter a couple of days ago so that poses no real obstruction.

@Seb, the vent tube is OK too, thanks for the pointer :thumbsup:

@Bailey about any carburated engine can run gravity feed, but I am a little worried about milage and if I run out of fuel far before reaching reserve.

I'll PM JZH, I think he runs gravity feed on his 3rd gen.

[AndrewNS]

I don't know anything about the mini pump you were thinking of using, but I can tell you that almost any motorcycle pump for a carb'd bike will work. They are all low pressure (3-4 PSI, I think). So finding a compatible pump at the breakers and adapting it might also be an option.

I have an '86 VFR, and when its pump died I discovered that a variety of later model Yamaha and Kawasaki models use the same model of Mitsubushi pump. I bought one off of a 2002 YZR600 Yamaha and just swapped the electrical parts over to my old pump to make it work again. But the body was exactly the same, and it would have fit in the same mount. I used the old body 'cause the fuel lines on the new pump came out at a slightly different angle and I was too lazy to swap over the electrical plugs. But the guts were exactly the same, just 15+ years newer.

[SEBSPEED]

@Seb, the vent tube is OK too, thanks for the pointer :thumbup:

That's good, but clean the underside of the gas cap well also, I think there is a small vent there too!

[V4 Rosso]

All went well and even riding the Nordschleife on gravity feed with the tank half full did not made the bike surge at any point :fing02:

I did however fill her up a bit sooner than I am used to, I got her down to about one and a half gallon left in the tank and it did not feel any different than with a fuel pump.

Douglasthecook had a spare that we installed yesterday and now I can safely extend my rides without needing to fill her up again.

[SEBSPEED]

Good to hear Rosso! :fing02:

[JZH]

All went well and even riding the Nordschleife on gravity feed with the tank half full did not made the bike surge at any point :goofy:

I did however fill her up a bit sooner than I am used to, I got her down to about one and a half gallon left in the tank and it did not feel any different than with a fuel pump.

Glad it worked out for you--I was on hols and missed your PM. I, too, didn't want to find out if there would be a problem at near-empty, but I never had a hiccup.

Ciao,

[mechdziner714]

Carbs work fine off gravity feed, I havnt done it on that particular bike but have on several others.

[SEBSPEED]

All went well and even riding the Nordschleife on gravity feed with the tank half full did not made the bike surge at any point :fing02:

I did however fill her up a bit sooner than I am used to, I got her down to about one and a half gallon left in the tank and it did not feel any different than with a fuel pump.

Douglasthecook had a spare that we installed yesterday and now I can safely extend my rides without needing to fill her up again.

I want to try this setup (on purpose) with a 4th gen. I'm wondering if you did any extended high-rpm riding with the gravity feed? I'm hoping to save space/weight for a track-type bike... Thx!

[V4 Rosso]

We didn't ride The Ring at race pace but the lap around the Nordschleife (20+km) had plenty of high rpm & WOT and it didn't miss a beat.

[SEBSPEED]

We didn't ride The Ring at race pace but the lap around the Nordschleife (20+km) had plenty of high rpm & WOT and it didn't miss a beat.

Awesome, thank you!