Using an in-tank electric fuel pump with a carburetor

You can use an in-tank electric pump on a carburetor by using a Holley 12-803 or "knock off" sold on eBay, but beware of those sold by eBay sellers skipwhite, whiteperformance or abad71camaro on eBay OR use a ready made solution to this if to you money is no object right here.  =>  B004I595V8


For the do it yourself method - you will need a by-pass regulator on the return line to regulate the feed  pressure down to 15 psi .  You can get a genuine Holley 12-803 from us => HERE


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The article will show you how to set up an in-tank electric fuel pump capable of pushing 100 psi - like an e3270 or e3240 etc - to fuel a carburetor safely down at 3 to 12 PSI.


Now before you go further - remember . . .  there IS a ready made solution to this if to you money is no object right here.  =>  B004I595V8


A word on fuel pumps - if you are replacing yours - if you put in the part number of the pump in an Internet search - you will get listings - some of which are very low prices.  If you look closely at the listing - like if it is on eBay, you will see that it is a "house brand" - meaning it is a Chinese or Korean knock off.  TRUST ME - no matter what kind of "lifetime warranty" it offers, you want to STAY AWAY from those pumps.  They have been known to actually melt the pump head as it failed only after about six months and then seized up.  If the pump is in the tank, it is not a job you want to be doing over and over again - replacing the pump.  Get a genuine brand name like Delphi, etc.  At this writing the difference of $29, versus $46 for the real thing on an e3270 - the $16 you save is not worth the headache to replace it in 6 months.  Many say to stay away from Airtex, it is your preference.


For instance, EP241 ( E3210 Airtex) = Flow= 40 gph & PSI = 65-75   That pressure reading is right on the head of the pump at the lab and if you take into account filters and lines and lengths, it’ll probably equate to 50-55 psi capable up the line.


The EP381 pump used in the early vortec trucks, cyclones, etc is a better choice => EP381 (E3270 Airtex) = Flow = 50-60 GPH & PSI = 80-90, which means it should yield a 70-80 psi up the line in a vehicle.  The Vortec uses 19 pound injectors at 60 PSI in that spider poppet configuration.

An Airtex tech named Craig confirmed these numbers above and said . . .  quote “ you should never use a EP241 on a vortec or LS1 motor”  He explained that it would work but the pump would be working itself to death to maintain the pressure and that would shorten the lifespan dramatically. He also explained that the EP381’s were manufactured with a new thin magnet design which yielded a lot higher torque that the EP241’s. They were specifically designed to work on Vortec & LS1 style engines. Also he said the current draw on the EP381 would be significantly less than the EP241, less current = less heat=longer life.  The EP241 is designed to work with TPI & not MPI and should only be used in that 45 PSI  application that a TBI is.


The eBay sellers are selling fuel pressure regulators that may have been defectively made with a 1/4 inch check ball when the design calls for a 5/16 inch ball.  The result is the ball can sit off to the side, never close, therefore never regulate, and thus possibly flood your carburetor and cause an engine fire.  You can get a genuine Holley 12-803 from us => HERE


Here is a link to the complete volley of an email that went back and forth to the "skipwhite" eBay seller's company => .   This seller sells everything Korean and Chinese of the American brand name  "knock-offs" copied from American brand names like Holley - and  the Chevy small block "procomp" aluminum heads and has a girl named "Sabrina" in the office handling "customer service" that not only does not know anything about vehicles or engines, but will get nasty in an email after she goes in circles not understanding anything you just wrote to her about an issue of an item you bought from them.


In all honesty, even an actual Holley 12-803 or 12-804 fuel pressure regulator has a good chance of having the wrong size check ball in it also - as the actual Holley one I bought did.  You can get a genuine Holley 12-803 from us => HERE


The short story on how this is done is to put a "pressure plate" (valve) style regulator on the feed line with a "T" in the line to the 12-803 Holley or "knock off".  By "knock-off" this  means a foreign made Chinese or Korean "copy" of the Holley 12-803 / 804 regulator.   Then open up the screw adjustment setting (counterclockwise will open the plates) on the pressure plate style regulator to allow most of the fuel to return to the fuel tank - and set it to about 15 psi.  You just dropped a 100 psi capable fuel pump to safely feed the regulator which will feed the carburetor.


To be frank the "pressure plate" style regulators like the one shown in the pictures (the gold one) do not regulate well, and are really hard to get adjusted.  If you are trying to use one to be the first step down regulator, it is more likely to pulsate wildly to get down to 30 or 40 psi - even with a vacuum reference and to honest is it not worth it.  You can try it, and you could even try a brass needle valve, but one of our regulators is the best shot to take => AVAILABLE HERE   You can use a pressure plate syle one for the secondary - pre 12-803 regulator - as it will act as a pressure buffer.  Even though it will READ the same pressure as the first line pressure - it will actually be slightly less on the inlet to the 12-803 - otherwise the 12-803 is likely to stay hard shut under the straight pressure on the check ball valve.


Think of it this way.  A conventional air line at the service station for filling you car tire has probably 120 psi in it.  The valve to the tire however is a restriction such that all that pressure cannot get through at once to instantly fill the tire.  In fact it will take some time before the pressure in the tire could ever reach the same as in the line.  This has to do with the VOLUME of air that can pass the valve as a restriction, not the pressure the line it has.   In the case of the 12-803, at a certain pressure over around 20  to 30 psi - it will actually lock off tight, as the spring on the diaphragm - depending on how much you have adjusted i "down", - will not be able to open the ball against much more pressure than 30 psi.  In this case while the pressure on the second regulator may "read" more than 40 - maybe up to 70 even, but the amount of fuel that can get past it (or if high enough even forced past  the check ball of the 12-803) is less in terms of volume.  This means the fuel bowl of the carburetor  may fill very slowly due the low volume of fuel that can get past the regulator actually acting more as a valve.   If you use TWO regulators, vacuum modulated, you will have a very safe "see-saw" method where double regulation occurs.  The first regulator will increase flow and the other restricts it to keep pressure more even to the inlet of the 12-803 - restricting volume from allowing the carburetor to flood pass the needle valve.  You can get a genuine Holley 12-803 from us => HERE


With a Quadrajet at least - over 7 psi is in danger of just flooding the whole carb out through the gaskets and everywhere (with a hazard for an engine fire) - while between 4.5 and 5.5 is "ideal".  BUT . . . a Quadrajet can operate with as little as 3 psi on it with sufficient fuel volume, and will "limp" running with as little at 1 psi to it with sufficient fuel volume - you just will not be able to accelerate hard before the carb will starve dry.  So, you can run it really low on pressure as you manage to adjust the pressure slowly upward with road tests.  An engine will die in similar ways if it is flooded versus starved.  The key will be to get out and look at the gauge real quick to see which one it is.


Remember using vacuum reference the first regulator will increase line pressure on acceleration when vacuum drops and the second one will decrease pressure to the inlet of the 12-803 on vacuum drop.  When you stop and the engine is idling, the main line pressure will decrease slightly allowing more fuel to return the to tank.  Adjusting this with dual vacuum references will be a bit tricky.  Set the first primary line pressure - using one of our regulators is the best shot to take => AVAILABLE HERE  to almost as low as it will go - to 30 psi just after it will not adjust lower, then set the secondary one to just above 10 to around 15 if you are using one.  That is where it will be tricky - because as soon as the carburetor bowl seat shuts, it may bounce to meet the inlet line pressure and read 30 psi.   BUT - it really is not.  It reads 30 but the fuel volume is restricted by the secondary pressure plate regulator, so as the engine is running and consuming fuel at idle, the flow is restricted so the pressure when driving can be regulated successfully by the 12-803.  If you have a weaker electric fuel pump, you may not heed the secondary pressure regulator.


You MUST use a 12-803 diaphragm type pressure regulator, as the pressure plate regulator will not reliably be able to be set to 3 to 12 psi to feed a carburetor.  The line between the 12-803 and the carburetor will always be set to the pressure you set so the carburetor will perform properly.  You can get a genuine Holley 12-803 from us => HERE


The pressure plate type regulator is shown in the pic accompanying this article, and they are available from many sellers and on eBay for around $20.  You will need to remove the gauge, plug the hole, and move the gauge to the SECOND "T" in the feed line so you can see how much pressure you have against the 12-803.  (see the last pic)  The gauge threads are 1/8-27 NPT and you will need a 1/4 inch "T" and two 1/4 to 3/8 hose barb fittings and one 1/4 to 1/8 NPT bushing to mount the gauge.   You could buy an extra regulator instead of the "T" as shown in the pic - and if you cannot get the pressure down to 15 psi - this may be required - but normally  to do so is a waste of money.  Again,  one of our regulators is the best shot to take => AVAILABLE HERE 


The problem with this design of pressure plate style regulator is that the slightest amount of debris - like a piece of silicone or telfon tape sealer you might have used elsewhere in the fuel system breaks loose and travels into the pressure plate regulator - and if it hits the regulator inlet - it will more than likely get stuck between the plates and cause it to NOT regulate properly or smoothly or if even at all.  Meaning it will not pass through and down one of the four holes to get out.  You would need to open the unit and manually check for debris obstruction to remove it.


There are other designs like this available too that do not suffer from this design flaw.   Again,  one of our regulators is the best shot to take => AVAILABLE HERE 


These "pressure plate" type regulators as the one shown are only good for smooth adjustable pressure from 30-70 PSI, with a vacuum reference even though the gauge reads from 0-140.


It will be tricky to get to 4.5 to 5.5 psi set for a Quadrajet.  If you put too much pressure on the inlet to the  12-803 regulator, it will pretty much lock shut and will not regulate.  Frankly they were designed to take about 18 psi max on the inlet, but with careful adjusting you can make them work with up to 30 psi - but not much more.  A better solution IS to use a dual regulator set up to step the pressure down with a second vacuum referenced regulator in front of the 12-803 like the drawing shows.  This might help lengthen pump life by letting you keep a factory head pressure on the pump - according to "Craig" at Airtex above.


However . . . if you put too much pressure on the 12-803 directly - when driving it will not regulate and the engine will die with a high head of pressure on the 12-803 - because the spring in it can only push open the check ball in it to overcome either pulsating pressure or 18-20 psi easily.  With 30 psi on the 12-803 inlet, you will need to crank the regulator down pretty much to the bottom of its adjustment.  With that high of a head of pressure on a 12-803 inlet, there is always a good chance the pressure will cause too high of a volume of fuel at the carburetor and flood it anyway.


So if it is like an EP241 you are using - keep 45 PSI on the return line side and tap on the side with another regulator to drop to 15-20 psi, and if it is something like an EP 381 (e3270) keep 60 psi head on the return line and the same on the tap side to the 12-803


Remember to solve or prevent vapor lock you will want as high a pressure as possible at the carburetor - or plumb the bypass to the tank and 12-803 as close to the carburetor as possible.


For even pressure to the carburetor, you MUST use a vacuum or boost reference otherwise the fuel pump may "pulsate" at lower rpm or when first starting a cold engine.  Remember as you drive - and vacuum drops slightly, the pressure will correspondingly rise.   These pressure plate regulators are compatible with gasoline, alcohol (or gasohol blends) or diesel fuel, but at lower pressures, the slightest turn of the adjusting screw may leap the pressure up or down and it will be tricky to get set where you want it - and then when you tighten the lock nut - it may change again.  Regardless - you MUST avoid the pulsation or cavitation effect.



So, remember there IS a ready made solution to this if you money is no object right here.  =>  B004I595V8


Fuel pressure will rise on a 1:1 ratio when referencing boost or vacuum through the ,1/8'NPT gauge port on the top, and they come in various colors of Red, Silver, Gold, Blue or Black.


This universal adjustable fuel pressure regulator can be remotely mounted and adjusted manually.  Remote mounting by a bracket on ANY application that utilizes a return line.  The Boost/Vacuum reference is for use with turbo or supercharger systems or normally aspirated.


An option you might want to put on is a one way brass compression fitting ball valve that will hold a slight amount of fuel under a little pressure in the line when you shut off the key, and / or the Quadrajet has available an in carb filter that has an anti-drain back valve built into the filter so fuel does not siphon out of the carb backwards when you shut off the key.  These two things will ensure the pump does not spin really fast until it fills the line under pressure when you turn the key and that the engine will start quickly without excessive cranking.  Again in front of the secondary pressure plate style one of our regulators is the best shot to take => AVAILABLE HERE - it WILL NOT however regulate down lower than 30 psi.