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Thread: And Now the Fuel Pump :( Reply to Thread
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Topic Review (Newest First)
11-29-2010 11:18 AM
Baratacus that's just fine for the webber.
11-29-2010 08:50 AM
alternator Hay guys, I just found out the type of pump I installed. It is sold here at Mazda dealers, its model # is HEP-02A, the box says it is made in Japan, but it is actually made in China. Here's a link that shows a picture of the pump:
http://df2004.en.made-in-china.com/p...p-HEP-02A.html

It works perfectly with the 1.6L Carbbed engine.

It produces only 5 PSI fuel pressure, I think that's ok for the Webber carb.
08-08-2010 03:38 PM
fordem 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.
08-08-2010 03:04 PM
alternator
Quote:
Originally Posted by fordem View Post
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.
08-08-2010 02:46 PM
fordem
Quote:
Originally Posted by alternator View Post
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.
08-08-2010 01:29 PM
alternator
Quote:
Originally Posted by fordem View Post
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 )

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.
08-08-2010 10:21 AM
fordem 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.
08-07-2010 11:44 PM
alternator 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?
07-31-2010 04:00 PM
alternator
Quote:
Originally Posted by Baratacus View Post
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.
07-31-2010 12:40 PM
Baratacus 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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