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Discussion Starter #1
Ok, guys, I know I'm wining a bit after my 1.6L engine swap, please bear with me.

When I attempted the swap, I purchased the adapter plate and low pressure fuel pump from Low Range Offroad. Ever since the engine swap, the fuel pump has been making this ticking noise. I had it hooked up to the starter switch, so I went and hooked it up to a relay and gave it power directly from the battery, but the ticking did not go away.

Today I was driving the Zuk to the dunes, and my fuel pump just stopped working. Aparently I had a defected fuel pump, but I do have some questions:
1. Does the fuel pump require a pressure regulator?
2. If the fuel pump is hooked directly to the carb, where will the excess fuel go? I didn't do the installation myself, so I'm not sure if it is going directly to the carb or through some regulator.

Please help!
 

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some pumps are internally regulated. most inexpensive ones require an external regulator. There should be a fuel return line so that anything the carb can't use gets diverted back to the tank.
 

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Discussion Starter #3
some pumps are internally regulated. most inexpensive ones require an external regulator. There should be a fuel return line so that anything the carb can't use gets diverted back to the tank.
Ok, what are the steps required to do after a carbed 1.6L engine swap regarding the fuel pump? What is the required pressure of the fuel pump? Can I get an old GM fuel pump and use it on the Samurai?
 

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If you do a quick search on the forums for it I'm sure you'll turn up a couple topics. Seems like we were discussing it at length a couple months ago and there's a bunch of usefull information in that thread.
 

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Discussion Starter #5
Hay, guys, good news. Ain't no problem with the pump, it was just disconnected from electricity.

I got down there tonight to remove it and claim a warranty on it, but I found the red cable disconnected. I connected it back and there it went.
 

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Discussion Starter #6
Now the pump really did die. I checked all electric lines, and they are all fine. I removed the pump. I made a search on the forum and most threads talk about the high pressure pump, none give details on low-pressure ones. I'm getting a new fuel pump, so I still need to know two things before I get it:
1. The pump was connected without any filters, before or after the pump. Could that have caused the pump to die after just several usages and less than 50 miles?
2. Do I need a fuel regulator? If so, do I need a one with a return line or without a return line?

Please help guys.
 

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samurai needs a low pressure high volume pump. The stock pump puts out about 6psi. You need between 4 and 8, don't go over 8 and don't go under 4. If your pressure is unregulated and too high the pump will unseat the needle valve in the carb.

You need a return line before the regulator. That way any fuel held back by the regulator can be diverted to the tank rather than loading up the fuel pump.

You need a fuel filter before the pump to avoid particulates going through the pump and damaging it. Particulates won't kill a pump but it will reduce it's efficiency.

What kills a pump is excess loading on the electric pump motor, either with excess backpressure, or excess draw pressure.
If you didn't have a return line that could have been causing a lot of backpressure which would dammage the valves on your carburetor and would burn out the pump motor.
Things that cause excess draw pressure are clogged in-line filters, clogged or restricted supply lines, or a malfunctioning tank vent.
 

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What needs to be determined here is what sort of pump is being used, and what the manufacturer of that pump recommends.

I've been using electric fuel pumps for over two decades, and that includes installing them on cars that originally had mechanical fuel pumps, and not all of them require return lines.

Some of them (notably SU pumps as fitted to the classic Minis) also tick during normal operation, others don't, it depends on the design.

Also, whether or not you need a fuel pressure regulator will also depend on how much pressure your particular pump can deliver and how much the carburettor needs - if a return is required with your particular pump, where it connects will depend on the regulator.

Just as an example, one of my Suzukis is carburetted, has a low pressure, high volume, "in tank" pump, has no fuel pressure regulator and has a return line - tee'd in to the delivery line just before the connection to the carb - and this, by the way, is the factory setup - the only things that have been changed are the fuel filter (located outside the tank, after the pump by the way) and several small diameter rubber hoses.
 

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Discussion Starter #9 (Edited)
The fuel pump I got from Low Range Offroad and it is a universal one. It clearly said in the manual that the fuel pressure regulator is optional.

Ok, all that brings up one more question: How to hook up a return fuel line back to the fuel tank in the Samurai, which is not designed for a return fuel line? Anyone has done it?

Second question: How does the return line junction? Is it only a T-junction before the carb like fordem described, or must it be through a pressure regulator that has a return line in it? How difficult or easy is it?

I have a feeling my pump really didn't need a pressure regulator, but was overwhelmed with the backpressure. Just a feeling. So probably if there is a way to have a return line without buying a pressure regulator, it might solve the problem.
 

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Never seen a carbureted samurai mechanical pump that didn't have a return line off the pump. (Of course I've never seen an in-tank electric pump on a stock carbureted samurai either)
If the vehicle used to have a mechanical pump at one time or another, then you should have a line from the tank that's been blocked off. Should be 3 hard lines coming into the engine compartment: supply, return, and vent.
If the vehicle used to be Throttle body injected and had an in-tank pump then you could just run a return line.

As far as the regulator goes, if its a low pressure pump rated at under 8 psi then there isn't a need for a regulator. With no regulator in-line, you just put a "T" fitting in the fuel line between the carburetor and the fuel pump.
 

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Discussion Starter #11
Never seen a carbureted samurai mechanical pump that didn't have a return line off the pump. (Of course I've never seen an in-tank electric pump on a stock carbureted samurai either)
If the vehicle used to have a mechanical pump at one time or another, then you should have a line from the tank that's been blocked off. Should be 3 hard lines coming into the engine compartment: supply, return, and vent.
If the vehicle used to be Throttle body injected and had an in-tank pump then you could just run a return line.

As far as the regulator goes, if its a low pressure pump rated at under 8 psi then there isn't a need for a regulator. With no regulator in-line, you just put a "T" fitting in the fuel line between the carburetor and the fuel pump.

Baratacus, you solved my problem. That's exactly the answer I'm looking for. Yes, I used to have the mechanical pump in the old engine. I'll find that fuel return line and install a T-fitting on it. Thank you.
 

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Discussion Starter #12
Ok, guys, it worked.

I got a fuel pump from a local Mazda parts shop which is low pressure and externally mounted, and it worked. I hooked it to the carb through a T-fitting, so all extra fuel will be pumped back into the tank. It all worked very well.

I noticed on fourth gear, when I'm accelerating hard, after 5000 RPM the fuel supply to the engine falls short, but that's only on fourth gear, and probably fifth too but haven't tried yet. Could it be because the fuel pump pressure is insufficient?
 

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In my opinion it's not likely to be a low fuel pressure issue, but rather one of low volume ...

On a carburetted engine, inadequate (low) pressure is not that much of an issue - you can run most carburetted engines using a gravity feed system (supply the carb with fuel from a tank mounted higher than the carburettor) without a fuel pump - this is distinctly different to a fuel injection engine where the pressure is critical.

Carburetted engines are more sensitive to inadequate volume or flow than they are to low pressure - the fuel goes into a float bowl where the fuel level is held constant by the use of a float that opens & closes a valve - as the fuel is used, the fuel level drops and the float moves down opening the valve and as the fuel enters the bowl and the level rises, the float moves up and closes the valve. High pressure causes a problem because it forces the valve off it's seat, causing the fuel level to be high, and the engine runs rich, or in extreme cases, flooding and hydrolock can occur.

In a situation where the fuel flow is inadequate, the vehicle will, in most cases, run quite well, but sustained high rpm operation creates a situation were the fuel in the float bowl is used faster than the bowl can be refilled, and the mixture leans out and the engine splutters & eventually dies - this WILL happen in any gear, although it may be more noticeable in the higher gears, because this is typically where the engine stays at high rpm long enough to drain the float bowl.

First question - what is the spec of the pump you are using - what is the rated delivery volume at what pressure? If the pump cannot deliver the required volume of fuel required to run the engine (it probably does, because it is hard to imagine a fuel pump that can't deliver the fuel required to run a 100hp engine) - but if the pump doesn't have this capability, then it's no point in looking elsewere until you correct this problem.

Second question - do you need a return line and what size return line? Can the pump be "dead headed" or allowed to run with no flow - this is an issue of the pump design. If the pump can not be dead headed, a return line IS required to prevent pump damage, and the return line needs to be correctly sized (smaller than the delivery line) so that you do not have a situation where the fuel the engine needs is being returned to the tank instead of delivered to the carburettor. If the pump's rated delivery volume is significantly higher than the engine's fuel requirements then a correctly sized return line would be advisable.

Third question - do you need a regulator? This is a matter of comparing the pump's maximum delivery pressure (which, by the way is different to it's rated delivery pressure) to the caburettor's maximum acceptable pressure - if the pump delivers more pressure than the carb can handle, a regulator IS required.

Given the situation you find yourself in I would try running the engine at 5000 rpm in the lower gears & holding it rather than changing up to see if it will run out of fuel there also - if it doesn't, then fuel delivery is not your problem, if it does, I would look at the size of the delivery & return lines, make sure the return line is the smaller of the two, and then attempt to restrict the return line - if it's rubber hose, find a way to squeeze it off and see how this impacts the problem.

If you are having a delivery volume problem AND if the pump can be deadheaded, consider removing the T and not using a return line.
 

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Discussion Starter #14 (Edited)
In my opinion it's not likely to be a low fuel pressure issue, but rather one of low volume ...

On a carburetted engine, inadequate (low) pressure is not that much of an issue - you can run most carburetted engines using a gravity feed system (supply the carb with fuel from a tank mounted higher than the carburettor) without a fuel pump - this is distinctly different to a fuel injection engine where the pressure is critical.

Carburetted engines are more sensitive to inadequate volume or flow than they are to low pressure - the fuel goes into a float bowl where the fuel level is held constant by the use of a float that opens & closes a valve - as the fuel is used, the fuel level drops and the float moves down opening the valve and as the fuel enters the bowl and the level rises, the float moves up and closes the valve. High pressure causes a problem because it forces the valve off it's seat, causing the fuel level to be high, and the engine runs rich, or in extreme cases, flooding and hydrolock can occur.

In a situation where the fuel flow is inadequate, the vehicle will, in most cases, run quite well, but sustained high rpm operation creates a situation were the fuel in the float bowl is used faster than the bowl can be refilled, and the mixture leans out and the engine splutters & eventually dies - this WILL happen in any gear, although it may be more noticeable in the higher gears, because this is typically where the engine stays at high rpm long enough to drain the float bowl.

First question - what is the spec of the pump you are using - what is the rated delivery volume at what pressure? If the pump cannot deliver the required volume of fuel required to run the engine (it probably does, because it is hard to imagine a fuel pump that can't deliver the fuel required to run a 100hp engine) - but if the pump doesn't have this capability, then it's no point in looking elsewere until you correct this problem.

Second question - do you need a return line and what size return line? Can the pump be "dead headed" or allowed to run with no flow - this is an issue of the pump design. If the pump can not be dead headed, a return line IS required to prevent pump damage, and the return line needs to be correctly sized (smaller than the delivery line) so that you do not have a situation where the fuel the engine needs is being returned to the tank instead of delivered to the carburettor. If the pump's rated delivery volume is significantly higher than the engine's fuel requirements then a correctly sized return line would be advisable.

Third question - do you need a regulator? This is a matter of comparing the pump's maximum delivery pressure (which, by the way is different to it's rated delivery pressure) to the caburettor's maximum acceptable pressure - if the pump delivers more pressure than the carb can handle, a regulator IS required.

Given the situation you find yourself in I would try running the engine at 5000 rpm in the lower gears & holding it rather than changing up to see if it will run out of fuel there also - if it doesn't, then fuel delivery is not your problem, if it does, I would look at the size of the delivery & return lines, make sure the return line is the smaller of the two, and then attempt to restrict the return line - if it's rubber hose, find a way to squeeze it off and see how this impacts the problem.

If you are having a delivery volume problem AND if the pump can be deadheaded, consider removing the T and not using a return line.
Fordem, your post is a bible to me. So much useful info, thank you.

To answer your first question, I really could not find any specs on the fuel pump, not volume nor pressure. It is a Mazda pump and I don't even know which Mazda :) (I know, shame on me :p)

Second question, I don't know if this pump requires a return line or not, but I did not have a return line for my previous pump, and it got damaged. So I don't feel comfortable not having a return line there. But I will try your suggestion, fit a clamp on the return line to increase the pressure there, maybe that will improve the fuel flow into the carb.

Third question, I'm quite positive I will not need a regulator, because the pressure of the fuel pump is obviously low; when I first installed it I turned on the ignition switch without firing the engine, and left the fuel line open to see the fuel rate that is being pumped out, and it wasn't high.

Like you said, I'm suspecting too much fuel is passing back to the return line. I did try to hold the RPM above 5000 while idling, and there were no interruptions in the fuel supply to the engine. I'll try to do that on low gears, first and second, tomorrow and see how it goes. This is extremely important to me because driving on sand requires running constantly on high RPM, and all the terrain we have around here are sand dunes.
 

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Third question, I'm quite positive I will not need a regulator, because the pressure of the fuel pump is obviously low; when I first installed it I turned on the ignition switch without firing the engine, and left the fuel line open to see the fuel rate that is being pumped out, and it wasn't high.
Just so that you're aware of it - flow rate & pressure are different things, although, they are to some extent related, in that one inversely affects the other.

Flow rate is measured in terms of gph (gallons per hour - or it's equivalent) whilst pressure is measure in terms of psi (pounds per square inch - or it's equivalent) - and in any given situation as the delivery pressure increases, the delivered volume decreases.

A test like you did can be used to measure the flow rate - catch the fuel in a container and measure how much is delivered in a given period of time - but a gauge is needed to measure the pressure - you can estimate it by capping the line with your thumb and seeing how much pressure it takes to stop the flow.

I can understand your reluctance to operate this pump without a return line, but, it's a different pump most likely with different spec., and unfortunately those are not known.
 

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Discussion Starter #16
Just so that you're aware of it - flow rate & pressure are different things, although, they are to some extent related, in that one inversely affects the other.

Flow rate is measured in terms of gph (gallons per hour - or it's equivalent) whilst pressure is measure in terms of psi (pounds per square inch - or it's equivalent) - and in any given situation as the delivery pressure increases, the delivered volume decreases.

A test like you did can be used to measure the flow rate - catch the fuel in a container and measure how much is delivered in a given period of time - but a gauge is needed to measure the pressure - you can estimate it by capping the line with your thumb and seeing how much pressure it takes to stop the flow.

I can understand your reluctance to operate this pump without a return line, but, it's a different pump most likely with different spec., and unfortunately those are not known.
I guess I'll try to find more information on the pump I got. I got it really cheap, although it is made in Japan. Only about $18.
 

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If you can find out what Mazda vehicle it was used on that may get you much of the information you need, even if it doesn't provide - as long as the engine size, and power output are similar to or slightly larger than those of your engine, the flow rate will be adequate and knowing if the original vehicle uses a regulator and/or return line will help you determine if you need to have those.
 

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Discussion Starter #18 (Edited)
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