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Old 09-10-2009, 01:17 PM
crudeau crudeau is offline
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Default how to convert gravity carb to fuel pump??

I have an eton viper 50cc quad that I have been installing a 125cc vertical motor into. I have the engine installed and the drive axle flipped for lef tside drive. But now I need to figure out how to get fuel to the carb. The tank will be in front of the steering stem because of the engine height. Is it possible to use a fuel pump and some sort of catch can above the carb? I would much rather use some kind of pump setup that just involves fuel lines if possible.
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Old 09-10-2009, 01:40 PM
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get a fuel pump, run it directly to the carb, diaphragm pumps are easy and cheap.

Just wondering, how are you using a vertical shaft engine?
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Old 09-10-2009, 02:00 PM
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I had a Mikuni Jet Ski fuel pump on my Honda GX240 and it worked fine, but I think it may give me problems with the RM250. I plan to do a tiny surge tank above the float level (maybe on a bracket fabricated to fit on the 2 top reed cage screws), with 2 fittings in the bottom, another in the side, inlet and outlet on the bottom, return to the tank on the side, that way, the carb will be just gravity fed.
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Old 09-10-2009, 02:18 PM
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Here's the pulse fuel pump I use on my kart: http://www.google.com/search?sourcei...ikuni++DF52-73
I've been told the round Mukuni and Walbro brand pumps outlast the Mikuni square models.

Here's some good info on these types of fuel pumps:
http://www.mikuni.com/c-fuel_pumps.html
http://www.walbro.com/brochurefiles/...l%202-9-05.pdf

If your carbs needle and seat valves aren't designed to operate under fuel pressure you may run into flooding issues. If you do, one way to remedy this is to install a fuel return line system to lower the pressure entering the carb. To do this you can either purchase a pulse pump with dual outlets or simply install a "T" or "Y" fitting between the pump and carb on single outlet pump models. This returns some of the fuel back to the tank and lowers the fuel presure going to the carb. (you might also have to instal a fitting in the tank for this)

When I ran into flooding isues and had to install a return line for my Honda kart carb, I installed a Briggs inline fuel shut off valve http://www.google.com/search?hl=en&r...+valve&spell=1 in my return line so I could adjust the pressure level entering the carb by controlling how much fuel was returned to the tank.


If you experience flooding issues running a fuel pump, another option for you might be that Mukuni (and possibly some other carb manufacturers) sells 2 different types of needle and seat valves for some of their carb models. (the normal gravity-feed type and then also a special one designed to work with a fuel pump)

As far as your pulse signal to operate the pump goes, many motorcycle engines come equipped with a small unused vacuum fitting installed in the intake manifold. My Honda motor didn't so I drilled a hole and installed a 1/4" fitting into my intake.

These pulse pumps will also function off the pulse signal from the crank case of many small engines, so that might be another option for you.
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Old 09-10-2009, 05:50 PM
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The motor is a vertical 125cc but it has a horizontal output.

I attached a picture of the motor. I had to do some pretty extensive frame work to fit the motor. I do have a few spare jetskis floating around the yard. I have a 1989 seadoo sp round fuel pump I can yank out. Only problem I have with that is the crank pulse. There is a crank vent, that black house in the picture right in the middle top of the crank case. Can I use that as my pulse? From there I like the idea of the T or Y fitting and fuel shut off switch.

The other question I have is the charging output. I know this stator has the power wire for the CDI, but there is also a power wire coming out that has nothing to go to. Can I use this to keep a small 12volt battery charged? I was looking to put some fog lights and misc other things on the quad. I know I can use this wire to do that without a battery, but my concern is do I need a voltage regulator or any of that type of stuff.
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Old 09-10-2009, 06:24 PM
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if you say vertical that is refering to the shaft not the way the cylinder goes.
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Old 09-10-2009, 06:43 PM
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sorry I'm coming from the world of pit bikes into the go cart scene so to me that's a vertical motor and horizontal motors are whats in a pit bike. I'm probably never going to get it right since I dabble more with the bikes. lol
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Old 09-10-2009, 08:55 PM
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You might be able to use that crankcase vent tube, but you still need to somehow ventilate the engine. If you were to just install a simple T-fitting and try to do both here, you may not have a very strong pulse signal going to the pump.

But I was thinking if you instaled a T with a longer line and automotive PCV valve in the breather portion, it should help boost the pumps pulse signal and it can also help to keep dust from sucking back in your motor. (this is prety much the same way my Star race motor breather/pulse-tap is arranged)

Another option is to install a 1/4" pulse fitting behind a baffle in the valve cover. (the baffle helps to keep oil out of the line and pump)
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Old 09-10-2009, 10:41 PM
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can I tap the intake manifold? I was googling and saw that some people have done that with 2 strokes. The motor currently has a piece of tape of the intake port (manifold and carb aren't installed). If I rotate the flywheel, that piece of tape bubbles out and in with the piston stroke. So I'm assuming that would create a pulse? I'm not quite to familiar with how the pulse pumps work. I'm heading to bed but I guess that's what I need to research next. I would think the intake manifold would push gas and air into the fuel pump as it pulsed.
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Old 09-10-2009, 11:00 PM
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Yeah, a pulse fitting in the intake manifold should work great.

Simply put, the intake or crank case pulse signal alternates between vacuum and meyby slight pressure. When connected to a pulse fuel pump this alternating signal moves its diaphragm back and forth. This action draws and pushes the fuel along to the carb.
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Old 09-11-2009, 07:16 AM
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Pulse pumps will work off crankcase pressure, or vacuum pulses. All that's required is a pulse, IE, changing pressure. For a really strong pulse, you could do both, with check valves to keep crankcase pressure from entering the intake, and vice-versa.
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Old 09-11-2009, 11:15 AM
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I think I will go with the intake manifold. Seems easy to tap into. So I just need a 1/4" barb fitting. I assuming it will go into the top of it so fuel doesn't collecting in it. Then from that I will do the t splice on the pump to carb feed line. With a fuel switch for the preasure regulator. Awesome guys. thanks.
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Old 09-11-2009, 04:58 PM
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Your fitting in top of the intake should work out great.

You might not even need a return system. Usually guys just do a basic hookup first and see if their carb suddenly starts flooding or running way too rich. The only reason you'd want a return system is If your carbs needle and seat valve cant handle the increased fuel pressure. Lots of carbs/pumps work out just fine without a return.
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Old 05-07-2010, 04:28 PM
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---->>>-- Pushing fuel up return loop creates gravity feed pressure levels.
|...........|
|...........|
Carb.......|
^...........|
Pump-<<-

That should do it.
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