So I figured I would share this with all of you. The next couple pictured are plumbing for a professional looking fuel system. Got the webers/mikunis, now its time to get the looks. These were made with Powerpoint and the part#s are what i've used in the past. You don't have to get the same exact parts, its just what I wanted for my overall look. If you need better quality pics, PM me and I will send them your way. Shoots madoots

 

nice writeup man. very clear and detailed pictures

 

looks good cept...


wheres the regulator





buying a gauge in the next couple weeks so then ill have real pics installed but you should set it up like this:


not using the parts listed or pictured, but the same setup. fuel will flow from tank to pump to carb to regulator, and excess dumped in tank.



what is your current design going to do with excess flow or psi?


you need a diaphram bypass fuel regulator, or a decent mechanical (spring) bypass reg. barry grant makes a high quality and even flashy looking one in a couple different colors, what i went with and plan to buy a couple more.






the reason is this:

say you have a fuel pump that puts out 4psi @ 60gph, when the needle valve is closed or your on light throttle, it doesnt need that much fuel, so whats telling your pump to slow down?

they do make self regulating pumps (actuall race $hit) but they are obscenely expensive for one worth a $hit. far easier to set it up like above.



a regulator only regulates the fuel before it, like a pump only has the rated flow/psi after it. the regulator opens and closes to allow the excess to blow of into the tank instead of overpowering your needle valve and making you run rich.


also when your needle valve closes, it actually will raise the psi in the line, pump is still pumping with no where to put it. like your thumb over the end of a hose.

 

Your system looks good but I would like to add that you MUST use 1/2" or AN 8 size line on the fuel return line from the fuel pressure regulator to the fuel tank. If you do not, you will experience carb flooding and slow regulator response, especially with Webers due to their 1 PSI supply pressure requirement. Mallory has a tech article on just this subject. With Webers you MUST use a return type fuel pressure regulator and I would highly recommend that you use this type of fuel pressure regulator with the Mikunis. I currently run Weber DCOE 45 carbs and I ran Mikunis on my race motor. Great job on the your article though and it should be very helpful to many planing to use side draft carbs.

 

Cool write ups! I've always wanted to use AN fittings on my Mikuni's.

 

The first illustration looks fine, but I can't see how Nuffs version works putting the regulator past the carb(s) you need the regulator ahead of the carb to regulate pressure and feed the excess back to the tank.

The -AN fittings are great, but be preparred to spend a few bucks, I know

 

This is a photo of my carp setup. You can not see the Nitous system because it is hidden underneath the intake manifold.

 

the purpose of a regulator is to regulate the pressure on the needle valve right?



so with one before the carb, your just cutting down the flow. if you really need the flow all of a sudden you"ll wait for the regulator to open up. or inconsistent fuel pressure at the needle valve


with one after the carb, you have 100% flow at the needle valve. now the regulator works like a blow off valve. just getting rid of what you dont need.

 

A return-type fuel pressure regulator operates at almost constant flow. It by-passes flow, thus changing fuel pressure, based on demand from the carbs needle / seat position (fuel flow into the carb-pressure change). Both Webers and Mikuni carbs work with very low fuel pressure, 1 PSI for Webers and 2-3 PSI for Mikunis. You can increase the fuel pressure regulator's reponse time by installing a vacuum line to the vacuum sensing port located on the top of most return-type fuel pressure regulators. I run two return-type fuel pressure regulators, one for the carb system and one for the Nitrous system and each is set at a different fuel pressure / flow and both use vacuum line connections. The sizing of any fuel pressure regulator is critical and you must properly size the fuel pressure regulator for the application. I would agree with ShoNuff's method if you would be using a Holley, Edelbrock, Rochester or other similar carbs.

 

I still disagree, yes the fuel pressure regulator regulates the pressure to the needle and seat, the flow or volume is regulated by the needle and seat, a bypass regulator has an "in" port and an "out, or multiple out" ports, plus the bypass, the fuel has to go into the regulator to be cut down in pressure, then is sent to the carb, the volume only varies slightly because of the pressure cut, but the fuel pump volume is much higher than needed so its no loss, the carb still gets plenty of fuel, the excess volume is sent back to the tank through the bypass port.
By putting the regulator past the carb as in your diagram, you have say 10psi coming out of the fuel pump going to the carbs and regulator, how is the regulator cutting the pressure back to the carbs all the way to the pump? if the regulator was wide open its still 10psi, if its adjusted down to 5psi, how is it regulating the pressure back upstream, somehow the fuel has to go through the pressure regulator to be regulated.

 

i guess im assuming that most people would use a pump that is correct for the carb they are using.


like im using a 3.5-5psi @ 80gph, so 90% of the time the regulator will be wide open, then in high draw situations it closes up to allow the carb to take as much as it needs. as need lowers the bypass opens.




i dont see how a regulator can function before a carb with the carb being the end of the line. at some point the needle valve will be closed then over powered by the line no matter what you set the regulator at. fuel is still flowing to the carb, but the needle valve is acting like a cap. the regulator can attempt to dump all the fuel back into the tank but it wont send more fuel to the carb until a drop in pressure happens, so the line between the carb and regulator will have to drop to unacceptable levels before the regulator closes. that could be enuff time to have the float bowl empty.


this is not the first time ive had this argument with sombody about this, another good one over at www.celica-gts.com.

when i setup this system for the first time in the wagon, ill have psi gauges before and after the carb. want to prove my point.

im also going to sacrifice a 32/36 top plate so i can drill and tap a hole to get a psi reading in the carb before the needle valve. i want to know what happens to 3.5psi on a .5in line when it goes into the carb because the inlet and outlet are smaller (forget excat size atm). this may lead me to running a even lower psi pump cuz i think psi will spike going into the smaller hole, or psi will build before the carb by the flow being forced through a smaller hole, much like a regulator.

 

I,m not trying to make an argument out of it, really doesn't matter to me how someone else wants to set up their fuel system. I,m going on the assumption that most people use a performance pump that puts out more than enough volume and pressure then use a pressure regulator to adjust the pressure, if the pump was sized to the carb needs then a pressure regulator wouldn't be needed.
The volume output really doesn't matter as long as it can supply enough to keep the float bowl filled. Thats the idea of a high output pump, it puts out enough volume to keep the carb supplied under any driving condition. The needle valve controls the volume, when the level drops the volume fills it back up, the excess is directed back to the tank, the pressure regulator is only there to control the pressure so it doesn't push the needle open by having too much pressure against the needle, theres no drop in pressure at the needle, just a drop in level that opens it up and allows more in. the extra fuel is just bypassing back to the tank.
I don't know what sacrificing a 32/36 top to put a pressure gauge before the needle will accomplish, the pressure is already set, possibly going from a 1/2" hose down to a 3/8" at the carb will give a slight fluxuation because of the restriction thats created, but once inside the float bowl it doesn't matter, the bowl isn't pressurized, its vented.

 

I second Nook's statement, every fuel system I've plumbed have had the reg before the carb. The port that opens in the reg when it's in open flow is more than enough to supply an exteemly built v8.

 

I have Webers, Holleys and Edelbrocks on my cars. I run the return-type fuel pressure regulators on the Webers only and I run direct-type fuel pressure regulators on the Holleys and Edelbrocks. You have to rememeber that Webers and Mikunis only run 1PSI and 2-3 PSI respectively, the return-type fuel pressure regulator system is the only type of fuel pressure control that will maintain these low pressures. I run 5-7 PSI pressure on the Holleys and 3.5-5 PSI on the Edelbrocks. So if you are running carbs in a high performance engine your fuel pump output can be from 12-15 PSI, your regulator can be set to 5-7 PSI and the response time for the fuel pressure regulator to respond to the pressure change, caused by the opening and closing of the needle / seat, is sufficent if the fuel pump can supply the volume of fuel required. I run a Mallory 110 series pump on my Webers and a Mallory 140 pump on my Holleys and Edelbrocks. I dyno pull 285 HP on the Weber equipped motor, 750HP on the Holley equipped motor and 650 HP on the Edelbrock equipped motor and in all cases I have never run lean due to lack of fuel. All of the fuel pressure regulators are installed before the carbs. You MUST size the fuel pump, pressure regulator and all supply / return fuel lines for the horsepower and application you are going to utilize.

 

ShoNuff, your system will work if you use a differential-type pressure regulator. They do not have a unit like this for automotive applications but they do have them for industrial liquid burner applications. The regulator would be mounted after the carbs on the return line and a sensing line would be installed just before the carbs. You measure the pressure at the carbs and the pressure on the return line then set the desired / required differental fuel pressure that you want to maintain (pressure at the carb needle / seat). The reason you can not use an automotive fuel pressure regulator is due to their method of inlet / outlet pressure sensing.

 

Yeah, I agree with what you say above, earlier you agreed the other way regarding regulator placement?
The setup Nuff showed is still a useable configuration but not for a street engine that has to cope with variable driving conditions, that setup is for a full tilt pedal to the metal drag race setup that uses an adjustable pressure set fuel pump and a diaphram style regulator to maintain a set pressure at the carb(s)

 

no worrys nook, a good net argument ends up bringing up all of the info, id rather have more different opinions then someone believing what somebody says is gospel.




but i must point out the stock toyota carb...


it is regulated after the carb by the factory. the inlet is wide open and the return is essentially the same size as the inlet, but capped off with a tiny hole in it to bleed of excess.


the diagram i posted is from the barry grant website. utilizing their diaphram bypass regulator. i do have that already, this is the way it was designed to operate.


i want 100% flow and a rock solid psi at the needle valve regardless of the fuel demand, and i just dont see how that is possible with the regulator before the carb. the carb could feasibly run out of fuel before the regulator realizes it needs to allow more through.

also im not looking for the psi in the bowl, but in the chamber created by the inlet, outlet, and needle valve.



seems to me the regulator before the carb would be less "stable" on the street. like romping on it between lights, then you come to a stop and there just isnt enuff flow available so you starve when the low fuel in the bowl sloshes forward. and if like nook said you have "too much" fuel pump you are constricting the flow in order to get the psi your after.


think im gonna rig up a lil test using both types of setups and both a poppet and diaphram style regulator. bet $5 i can make the poppet style regulator over power the needle valve while still returning fuel to the tank. i also bet that "my way" wont, but still maintain correct pressure at the carb.

 

I still believe the fuel pressure regulator should only be positioned before the carbs and all my vehicles are done this way NOOK but I thought I would throw the differential-type pressure regulator into the equation because it would work if ShoNuff wanted to use the type of system he describes. I also agree with you NOOK about streetability of the system proposed by ShoNuff. I like things to work all of the time without continuously adjusting them. I can start up any of my vehicles and head to a cruise night without "Playing" with something.

 

I can not count the number of people I have tried to help who were installing Weber or Mikuni sidedrafts on a Toyota 4 cylinder motor. They are really different then Holleys, Edelbrocks, Rochesters, etc. carbs and most of the people were trying to adjust their sidedrafts like those noted above.