Thread: Fuel Pump and carbs question..

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I've got a small car powered by a motorcycle engine. Normally the motorcycle engine's fuel is supplied by a gravity fed gas-tank that is physically located above the carbs so naturally the fuel doesn't need to be pumped.

My gas tank is sitting on my floor pan well below the carbs (about 20" below). I'm going to try using a walbro electric fuel pump to pump fuel up to the carbs, but I'm concerned I might end up flooding them. The pump I'm using says it won't flood my carbs, and it somehow senses the float level and shuts off when no more fuel is needed. It's a bellows pump and I have no idea how it can sense float levels accurately so I'm a little skeptic -- does anyone know exactly how these work?

Link to the Walbro fuel pump I'm going to use

Does anyone know if this fuel pump is a good choice for pumping up fuel to a motorcycle engine (4-cyl w/4 carbs)? If not, does anyone have any better solutions? I installed this fuel pump last night, but I haven't tried using it yet. I'll probably test it out tonight but I'm curious as to what the correct pump would be, if this isn't it.

Thanks!

Adrian

Originally posted by techinspector1
Adrian, when we used to race karts we used pulse pumps which would operate off the pos-neg-pos-neg pulsing of the intake tract. Unlike your carbs though, ours had no float or bowl. I would think the pump you have in mind would work fine for your application. Here are links to the type of pump we used.
http://www.tsracing.com/store/showde...=1007&CATID=34
http://www.tsracing.com/store/showde...=1000&CATID=34
http://www.tsracing.com/store/showde...=2264&CATID=34

Did you have to prime the fuel line initially, or would this pump do it for you? I do have a vacume line on one of my carbs that normally connects to the fuel petcock (I beleive the vacume opens up the petcock) but I'm not sure if the vacume also regulates the fuel flow, or if it's just used to open-close the petcock when the engine is running vs. not running. I'm wondering if I could power one of your pulse pumps using the petcock vacume line.

I'll try out the electric fuel pump I have tonight. It's one hell of a LOUD pump though -- it sounds like a jack hammer. They say the pump won't flood my carbs, but from the noise the pump makes (Just tested it for 1 second), it sounds like I could drive my 150 PSI air compressor with it

Adrian

your motorcycle work al little diffrent then a car your 750 motor has a CV witch stands for constant-vacuum carb The Cv carb has a butterfly valve this is a thin flat disc . That fit in the venturi between the throttle valve slide and the intake valve slide and the intake manifold it job is to open or close the body of the carb to sheild it from ( or expose it to ) the vacuum created by the engine to control the action of the butterfly valve. The butterfly valve located on opposite side of the carbs venturi, controls the amount of air being drawn into the mixture chamber Ok then when you press the throttle for an increase in speed you open the butterfly valve between the carb and the engine .The vacuum from the engine is tranferred into the carb and travle through the suction passage into the carb this causes a vacuum to the top part of the slide witch causes it to rise at the same time air is entering the carb from the intake side and is causeing a pushingup effect ont the bottom of the throttle side the result of the combind"pulling on the top and pushing from the bottom make the slide rise as it dose so the tapered jet needlelift up in the needle jet permits an increased of fule to enter and be atomized with the stream .The C.V. carb can be thought of as a demand system it opens in keeping with the engine demands a fule pump will not work you need to mount the tank above the engine for the engine to perform properley if you hook up a fule pump you will just dump fule and flood it

Originally posted by PsychoKart
Did you have to prime the fuel line initially, or would this pump do it for you? I do have a vacume line on one of my carbs that normally connects to the fuel petcock (I beleive the vacume opens up the petcock) but I'm not sure if the vacume also regulates the fuel flow, or if it's just used to open-close the petcock when the engine is running vs. not running. I'm wondering if I could power one of your pulse pumps using the petcock vacume line.

I'll try out the electric fuel pump I have tonight. It's one hell of a LOUD pump though -- it sounds like a jack hammer. They say the pump won't flood my carbs, but from the noise the pump makes (Just tested it for 1 second), it sounds like I could drive my 150 PSI air compressor with it

Adrian

you need that pep cock to control the amount of fule to each carb it basically is your fule pump sorry techinspector1 I will have to dissagree with you a fule pump like your saying will not work

Originally posted by techinspector1
Wow, thanks for straightening me out, John, I had no idea they worked like that.

unfortunately I know very little about harleys and more about jap bike I repair and restore them retirement sucks i got to have something to do right now Im putting a 1100 xs motor in a golf kart

Well, I really need my fuel tank on my floor pan so I need to figure something out. I guess I could install a very small tank on top of the engine, and have a fuel pump constantly pump fuel up to the small tank, and have a over-flow line right back to the fuel tank on the floor, so it would basically circulate fuel constanty up to the small tiny tank above my carbs. How does that sound?

Oh, you said the petcock vacume line regulates fuel flow? I don't understand how the petcock works really.. Does the vacume line Open/Close the petcock valve, or does more vacume presure alow more fuel through the petcock, and less vacume pressure let less fuel through? I thought the only purpose of the petcock vacume line was to "shut off" the petcock when the engine wasn't running, otherwise the petcock valve was fully open when the engine is running?

Thanks,

Adrian

PsychoKart when you get your fule system figured out you will also have to have those carbs synchronized . if you know any wone that can do that for you that would be great if not you will need synchronizeing gage they make to type 1 is 4 vacuum gages in a row but if you have never done it before ithey can be a bugger the sceond type is mercury type their a lot cheaper and easer to use

The GS750 engine was running great before I stripped the bike down -- carbs were synced, timing is perfect, not too rich, not too lean, just right. Do I need to re-sync the carbs because the fuel pressure (Original gravity fed tank) will now be a little different because of my new fuel system?

Thanks,

Adrian

Originally posted by john gemmer
PsychoKart when you get your fule system figured out you will also have to have those carbs synchronized . if you know any wone that can do that for you that would be great if not you will need synchronizeing gage they make to type 1 is 4 vacuum gages in a row but if you have never done it before ithey can be a bugger the sceond type is mercury type their a lot cheaper and easer to use

Originally posted by PsychoKart
Well, I really need my fuel tank on my floor pan so I need to figure something out. I guess I could install a very small tank on top of the engine, and have a fuel pump constantly pump fuel up to the small tank, and have a over-flow line right back to the fuel tank on the floor, so it would basically circulate fuel constanty up to the small tiny tank above my carbs. How does that sound?

Oh, you said the petcock vacume line regulates fuel flow? I don't understand how the petcock works really.. Does the vacume line Open/Close the petcock valve, or does more vacume presure alow more fuel through the petcock, and less vacume pressure let less fuel through? I thought the only purpose of the petcock vacume line was to "shut off" the petcock when the engine wasn't running, otherwise the petcock valve was fully open when the engine is running?

Thanks,

Adrian

the pep cock W/dyophram like you said it act like a fule pumo but also regulates flow what concerns me is a motorcycle run off a diffrent amperage then a car so if you use a automotive fule pump you could damage your stater or could feed back and take out your elec system you could weld you up a frame on the back that you can mount a tank

Originally posted by PsychoKart
The GS750 engine was running great before I stripped the bike down -- carbs were synced, timing is perfect, not too rich, not too lean, just right. Do I need to re-sync the carbs because the fuel pressure (Original gravity fed tank) will now be a little different because of my new fuel system?

Thanks,

Adrian

with the added fule presure it may not even run it may just flood out or even worst blow back and catch fire

Originally posted by john gemmer
the pep cock W/dyophram like you said it act like a fule pumo but also regulates flow what concerns me is a motorcycle run off a diffrent amperage then a car so if you use a automotive fule pump you could damage your stater or could feed back and take out your elec system you could weld you up a frame on the back that you can mount a tank

I completely re-wired everything and the fuel pump is driven off the ignition switch with an additional safety on-off switch. It's not running through the alternator, or the voltage regulator so it's not going to affect the system. I'm not using the original head-light either which definitely draws more current than my 12V fuel pump.

I want to keep my custom fuel tank on the floor only because it looks much better than on-top of the engine. If I absolutly can't get a good fuel delivery system working, then I'll mount a tank above the engine but that's the last thing I want to do really. I guess you could consider mounting your car's fuel tank on top of the hood the same thing Nobody want's it there.

So if I continue to use the pep cock, (Sorry, I was saying petcock If I use the original pep cock, with the vacume line, I should be able to use my existing pump to pump fuel into a small tank above the carbs, and when the pressure increases, my fuel pump should shut off, no?

Thanks!

Adrian

Originally posted by PsychoKart
I completely re-wired everything and the fuel pump is driven off the ignition switch with an additional safety on-off switch. It's not running through the alternator, or the voltage regulator so it's not going to affect the system. I'm not using the original head-light either which definitely draws more current than my 12V fuel pump.

I want to keep my custom fuel tank on the floor only because it looks much better than on-top of the engine. If I absolutly can't get a good fuel delivery system working, then I'll mount a tank above the engine but that's the last thing I want to do really. I guess you could consider mounting your car's fuel tank on top of the hood the same thing Nobody want's it there.

So if I continue to use the pep cock, (Sorry, I was saying petcock If I use the original pep cock, with the vacume line, I should be able to use my existing pump to pump fuel into a small tank above the carbs, and when the pressure increases, my fuel pump should shut off, no?

Thanks!

Adrian

well do what ya got to do have fun

Originally posted by john gemmer
well do what ya got to do have fun

Lets work through this! Solving these types of problems are what custom jobs are all about, no? So, we need to get fuel up to the CV carbs. Your saying the vacume line going to the pep cock should regulate fuel flow through the pep cock. The fuel pump I'm using produces 4 psi and should shut off when it exceeds 4 psi.

Any idea what the PSI is comming from the fuel line on a gravity fed fuel tank? I think it might actually be around 4 psi.. The fuel line is 1/4" it should be easy to calculate the PSI from the gravity fed tank if there is about 15" of fuel in the 1/4 line.

Adrian

Whops, it is a petcock. I thought that was right, but I want sure until I did a google search.

Adrian

Originally posted by techinspector1
Adrian, as a last resort, you could change to 4 kart-type diaphragm carbs and 4 pulse pumps. And by the way, the correct spelling is petcock.

Woah!! Changing carbs would definitely be a tuning challenge. Actually, I should look around and see if anyone makes a good fuel injection system for the GS750. I'd love to convert from points and carbs to electronic ignition and fuel injection. In fact, I'd like to get my hands on a programmable system that would let me experiment by writing my own EFI and Ignition firmware.

Adrian