What is the Max Fuel flow rate of a 150cc  By  dmartin95 (Read 8,210 times)

Hi Mr. Martin!

I just finished installing the new (lower pressure) electric pump.  New one is 2 to 4 psi; old one was 5 to 8 or 9.  As far as could tell, that higher pressure was not spitting noticeable fuel past the needle valve, but I wasn't comfortable leaving that high a pressure and trusting these little Chinese needle valves would do the job.  So a lower pressure pump - in the same range as yours.

What with daylight savings time it got dark early, so no pix.  I'll take a couple tomorrow.

Regarding regulation of pressure:

I considered getting this regulator, which can be dialed from 1 to 4 psi:


www.ebay.com/itm/141433732680?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

but probably won't unless a problem turns up.  At that low an output pressure i think it sane to just run the output of the pump into the carb - the vacuum pump got to the same pressure.  Remember - the pump only needs to have enough to open the needle valve when the carb fuel bowl runs low, and not so high the needle valve stops shutting off extra fuel when the bowl is full.  This isn't like an injection system, where you need to have a carefully regulated pressure (~50psi) because the pressure "regulates", along with the injectors and the duration they are open, how much fuel is injected.  In a carburetter system the quality of fuel consumed is not determined by the pressure of the pump at all.

It's POSSIBLE you might get marginally better bowl filling if you had a perfectly even pressure from the pump - and these do NOT give perfectly even pressure since they have pulsing diaphragms that push fuel out, and every pulse sends a wave of fuel (and thus a pressure pulse).  My belief this is negligible --- and remember --- the vacuum system operated the same basic way, except the diaphragm is driven by vacuum and springs, not a motor.  So the vacuum pump probably gives as much "pulsing" of pressure as does the electric pump - which is an unimportant amount.  But a pressure regulator would certainly help to even out the pressure leading to the carb if that's what you want.  I think it's chasing a problem that isn't a problem .... but who knows.

As for wiring the pump:

I used a simple relay (as is normally used in cars and motorcycles) - with a line from the key to the coil side of the relay (the other side to ground).  Thus, when the key is "on" the relay is closed, connecting the OTHER two terminals.  Then, you just run one of the other terminals to battery (use a small fuse inline), and the fourth terminal to the pump.  Of course, the pump needs a ground also.

About location:

I wanted to have the pump at carb level, so the pump's output pressure would be equal to the pressure at the carb inlet.  If you have an under floor gas tank (like mine), it would be "nice" to have the pump down near tank level so it need not suck any heights.  But, then, the small output pressure of the pump (say, 2psi) would NOT be the same as what you measure at the carb because of the column of gas in the 1 or 2 foot high fuel hose pushing back against the pump.  I didn't calculate how this would affect the pressure drop - probably unimportant for these pumps - but still something I worry about.  in MY case i had no choice --- there wasn't any place to conveniently mount the pump except to the front of the kickstand cross bar (just behind the gas tank).  Seems to work fine, but I'll let you know.

Hope this helps.
Pressure regulation is, i believe, a non issue.
Hook up is best with a relay so you are not drawing the "large" (~1 amp) current through your ignition switch.  Location is probably irrelevant also.  These things just work; not all that finicky.

How the carbs work is by the float and needle. The needle tip is made out of rubber and pointed so that it fits into the fuel inlet hole. When the needle is pushed up all the way it fits into the fuel inlet hole to stop fuel from coming in. As the fuel is used up the float moves down and the needle also now has less pressure and moves down some from the fuel inlet and allows fuel to flow into the bowl until AGAIN the float moves up and pushs the needle valve up into the fuel inlet and shuts off the fuel. This goes on constantly as the motor uses up the fuel.
Alleyoop

OK, about placement of the pump

I wired my new (small psi) pump up to see how high it could be and still suck up the gas from the underfloor gas tank.  There was no problem with the pump ABOVE the carb level.

That said, I ended up deciding to ,locate it down where the tank is - just to make sure it has not effort gobbling gas.  Here are a few pix showing the pump clamped to the kickstand cross bar.  Note - I took a 1 inch piece of radiator hose (rubber) to make sure neither the pump nor the clamp touched the cross bar.  That's just so the clicking of the pump is not transmitted through the frame of the scooter.  At first the pump is quite loud, but the instant it gets it's first gulp of gas it gets quite quiet.  Maybe the rubber isn't really needed ----













I know you said you didn't want to hear about wiring, but a few more cents.

You want the pump "on" when the key is on, and "off" when the key is off.  So, you want to go to a wire in the front that gets +12 volts when the key is "on".  It MAY be fine to simply splice into this wire, run a new wire back to the pump, and run the pump directly off this ignition wire --- but it's not great practice.  All standard electric pumps use a relay --- the wire from your ignition key ONLY causes the relay to close (very, very low current used), and the OTHER pins of the relay go (a) to the battery and (b) to the pump ---- so when the relay closes the pump draws right from the battery, not from the ignition switch.  These pumps are pretty modest in the current they draw --- probably about 1 amp --- so maybe it would not overload the ignition switch even if you just ran pump current directly from the switch.  But it's not a great idea; relays are cheap; just a good thing to do.

I think it was "scooter" (the guy who posted the great stuff about vac. pump psi) who mentioned having a separate switch that automatically closes whenever there is engine vacuum (as soon as you start the engine the switch closes; when the engine stops the switch opens), so you don't accidentally turn leave the key "on", with the pump running, and walk away - draining the battery.  My experience is the pump makes just enough sound (with the engine off) you will hear if it's still running - kind of a buzzer to let you know you left your key in the switch and the switch "on".  But it's certainty easy to add a switch in the wire running from the ignition key back to the relay.  Just FYI:  I don't have one.

The pump lists the MAX flow rate (gal/hr).  It won't pump MORE than that.  But our little engines only need 1% of that, so we are fine.

"Scooter" also listed fuel pressures at different RPMs.  With the vacuum pump the psi varied from 4 at low RPM down to 1.5 at high RPMs (if i recall right).  Anyway, the point is 2 or 4 psi is "normal" -=-- and that is exactly what your pump puts out.  So  THERE WILL BE NO PROBLEM!  Add a regulator if you are absolutely compelled to do so ... but, IMHO, it's a total 100% unnecessary waste of money.  Your pump is perfectly matched to these carbs, except it could, if needed, supply enough gas for a dozen carbs at the same time.  The needle valve in your carb will make sure it only pumps what is needed.

CIGARETTE LIGHTER ?

 It's used as a power port for charging cell phone, GPS, etc.... 




That is how I plan on mounting it.... it will only be inches away from the the fuel tank.....

Here's a video I made while back showing the scooters fuel system layout: