Fuel pump?

🇮🇹💦 Of the Loin /

So I have a shitty issue of not getting enough fuel delivered to the carb on one of my bikes when it gets below half tank (stupid derbi geometry)

I was thinking a low pressure in-line pump?

this one http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_x_18770015-P_x_x?cm_mmc=CSE-_-Google-_-VALUE3-_-VALUE4&ci_src=14110944&ci_sku=#utm_source=cse&utm_medium=google&utm_campaign=value3&utm_content=value4

perhaps? (yes I know its for a diesel)

I could also make it not rev as high and suck gas, but its a 50cc so what can ya do.

Re: Fuel pump?

hmmmmm you shouldn't have fuel delivery issues... I have a 70 metra and a tm24 in my frame at a craaaaaaazy angle and I can get every lost drop out of the tank.

Re: Fuel pump?

How about attaching a small tube from the overflow to an intake oil input so vacuum from the intake... no that won't work.

How about a small hose running from the exhaust to the fuel tank. Very little gases will have to flow through it, so by the time it reached the tank it would be cool, and that would create a small enough pressure in the tank to maybe help you out.

Re: Fuel pump?

Sidney Delicious /

This is a option that I have used on one of my Vespas w/ a similar issue of the carby sitting above the fuel line.

http://www.oldbikebarn.com/Mikuni-Fuel-Pump-1-Outlet-Square-Flush-Mount-14-l-hr

I usually tap the vacuum line into a spot on the intake to provide the needed suck.

Re: Fuel pump?

I think at 20-35 gph you're going to be flooding the crap out of your carb, way too much flow for a 50cc. Even the low value of 20 gph is enough for several 100 HP on a 2-stroke.

You could try with a very tiny needle valve but I think it'll overflow anyway, or at the very least will have a lot of trouble keeping a consistent fuel level. Obviously I could be wrong, I've never actually tested a pump with that kind of flow. Just saying that it sounds like it'll be a bit much :)

On vintage snowmobiles a very common pump is the little rectangular Mikuni one that flows 14 liters/hr, and that's enough for about 40 HP. So you should probably be looking for something that flows even less, maybe some kind of small aquarium pump would do the job? Not sure if those can handle fuel/oil tho.

Re: Fuel pump?

🇮🇹💦 Of the Loin /

yeah its a custom intake and a 21 dellorto so weird angle

I'm also always running high revs, because its a stock cylinder that I have to to keep up in traffic, so it drinks gas probably faster than your 70 metra!

I did see that mikuni pump, does it really work well with just a vaccum line on the intake? because maybe I will go that route...

Re: Fuel pump?

Sidney Delicious /

Yes sir, it worked well for me.

The setup was on a 125cc vespa w/ 28mm flatslide.

I had the vacuum line ported in to the intake, no overflow, no problems.

Words of advice...use stiff walled tubing (if it is too weak it will collapse during higher revs). Try to keep the vac line length under 12". Don't mount where it gets uber hot.

Re: Fuel pump?

Overpriced Parts /

Me thinks your inline fuel filter is restrictive. It would feel like I was running out of gas on my Gila/24mm flat slide magnum when less then 1/2 tank so I kept it full. This went on for 2 years worse in the winter. I changed the petcock, lines but kept the filter. Early this year the Lines were stiff/ hard / old so I changed them. For giggles I blew in the filter and it was almost completely blocked Though it looked new it was over 4 years old. Now with a new filter I could use reserve and the tank drains completely

Re: Fuel pump?

I'd second the vaccum fuel pump. Many scooters and lawn mowers use these, Solex mopeds too.

Re: Fuel pump?

And they act as petcocks too

Re: Fuel pump?

The properties of gas in a tank should be enough itself. A bunch of gas on top of eachothers, to a small 4-6-8mm hose. It pushes downward! That is a lot of force! However I am sort of having the same problem.

My hobbit petcock out the bottom left of the tank, runs about 18in to the other side, then it has to bend up and to the inlet on the carburetor which faces up. The fuel filter is never full of gas unless it tip it and let it sit there. I have tried removing the gas cap but that doesn't help the flow so my assumption is it isnt a vent problem. but I always have an air bubble in there.

I like that little Mikuni vacuum pump. Maybe that would work. I would just have to drill & tap a little vacuum port. ezpz!

I would feel better about the whole thing. Wonder if its ethanol safe.

Re: Fuel pump?

It doesn't matter if you have an air bubble in your filter. LOL.

Re: Fuel pump?

🇮🇹💦 Of the Loin /

yeah i dont have a filter (derbi tank is plastic duh)

its just the petcock comes hella far out. I'm gonna look into this, because I think it would make this bike totally finished

Re: Fuel pump?

does taking off your gas cap help? how about drilling drilling a hole in your gas cap bigger? maybe when your tank empties to around half its created a vacuum that the fuel cannot overcome

Re: Fuel pump?

Get a vacuum powered fuel pump if you feel gravity is letting you down, just install a T fitting and a return line back to the top of the fuel tank so it can redirect the excess fuel to source rather then over taxing the floatvalve and one day giving you catastrophic failure.

Re: Fuel pump?

walbro fpc 1-1

I bought a knock off one of these to handle the decrease in gravity fuel pressure as the fuel level gets lower. I haven't used it yet but I have to, I made my frame hold fuel and now it extends below my carb.

My idea was a constant return system. The pump would pump from the bottom of the tank all the way back to the top then into a barb fitting to drain back into the tank. Connected to the return line there would be a T and another fuel line to the carb. This way it'd trick the carb into thinking the fuel tank was always topped off. However I don't think intake pulses are strong enough at high rpm to run this pump, you'd need to drill and tap a hole for a barb fitting into your crank case to run the pump. Hope this helps you.

Re: Fuel pump?

damn rebel you beat me to it

Re: Fuel pump?

Rebel Moby Wrote:

-------------------------------------------------------

> Get a vacuum powered fuel pump if you feel gravity

> is letting you down, just install a T fitting and

> a return line back to the top of the fuel tank so

> it can redirect the excess fuel to source rather

> then over taxing the floatvalve and one day giving

> you catastrophic failure.

There's tons of motorcycles with fuel pumps and carbs that never have a problem. If you have an aftermarket carb (dellorto/mikuni/etc) then the needle and seat should be able to handle it.

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