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 Post subject: Re: From carbs to efi
PostPosted: July 5, 2019, 6:36 pm 
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Joined: June 4, 2007, 5:49 pm
Posts: 43
Location: morin heights north of montreal qc
I just received my new chokes and jets
Now im looking into getting a fuel pump
the problem is i know how fuel injection pump works and how the pressure is regulated and that there is a return to the tank
On one engine i have the fuel regulator is a T that is between the pump and the carb and the part of the T that goes back to the tank as a very small pin hole just to relieve the pressure
I have a holey fuel regulator but there is no return what happens to the pressure build up or is there something im missing


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 Post subject: Re: From carbs to efi
PostPosted: July 6, 2019, 6:12 am 
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Joined: December 22, 2006, 2:05 pm
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You’ve identified the main problem with controlling pressure with a hole when the burn rate changes. A spring loaded valve is required. I’ve used many different pumps over the years. I only use the carter 60504/ p90091/ 76438. It is an external tank inline pump designed like an efi in-tank pump but has a relief valve that limits pump output and load to 3.5-4 psi and comes with a pre-filter to protect the pump. Very quiet and I’ve never had one fail. The 15-19 gph rating is the only downside but I’ve used this pump on a 5.0l v8 and never noticed a lean issue on the top end from exceeding pump capacity but maybe I’m not trying hard enough. If it turned out to be an issue which I doubt greatly, at that price you could install a second pump in parallel which would heat and foam the fuel less than an efi pump bypassing most of its capacity most of the time. You could also switch between them if you have a pump failure or wanted to check pumps individually with a single sensor/gauge.

https://carter.opticatonline.com/part/b ... &ctx_iam=1

https://www.rockauto.com/en/moreinfo.ph ... 8412&jsn=3

You may be keen on using the original efi pump. Since most gerotor efi is going to flow more at lower pressure, any oem in-tank should be adequate if you can bypass enough and regulate it down enough. An adjustable efi regulator with a tee like what you have shown could be used if the spring is swapped for a soft enough rate or better yet, use a carb regulator as-is. Just need to figure out how large the tee orifice needs to be at idle to prevent pressure creep. Make sure the regulator is alcohol resistant or compatible. You will still have fuel heating from the high circulation rate and foaming across corners/edges inside the fittings.

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 Post subject: Re: From carbs to efi
PostPosted: July 6, 2019, 9:39 am 
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Joined: July 17, 2008, 9:11 am
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Location: West Chicago,IL
Carbie pumps do not use a return line. As MV8 stated, 2-4.5PSI pump is all you need. Any higher pressure and you risk over powering the needle valve in the carb's float bowl. Lower pressure is OK as along as the pump can satisfy your peak power needs in gallons per minute. I think about any low pressure pump you find at the local parts store should be OK.

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 Post subject: Re: From carbs to efi
PostPosted: July 7, 2019, 5:42 pm 
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Joined: March 30, 2011, 7:18 am
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Location: central Arkansas
rx7locost wrote:
Carbie pumps do not use a return line.


Actually, some do. Lots of late-60s and up cars did; it prevented vapor-locking with the higher underhood temperatures from emission controls and standard AC. Both mechanical and electric pumps had returns from the engine to the tank.

My 1984 Mazda B2000 had a particularly evil variant; it had an electric pump near the fuel tank. After the truck got to where it wouldn't maintain speed at 55mph any more I started serious diagnostics. It was running way lean, but I had good fuel pressure.

In the mess of hoses there was a tee in the fuel line, routing back to the tank. Pretty normal stuff. That's where hooked up the fuel pressure gauge. But - jumping past days of WTF? - the cheap plastic tee was *also* a fuel pressure regulator; it had a ball and spring inside, and the spring had gotten weak over the years, until it was easier for fuel to go back to the tank than to the needle valve... I discovered that entirely by accident; it wasn't mentioned in either the Mazda or Haynes service manuals.


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 Post subject: Re: From carbs to efi
PostPosted: July 7, 2019, 9:29 pm 
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Joined: June 4, 2007, 5:49 pm
Posts: 43
Location: morin heights north of montreal qc
After looking around and trying to figure out what prevents pressure build up cause the pumps continues to pump and no return like efi and even my fuel regulator no return so i was thinking if pump doesn’t stop the pressure will buid up between the pump and regulator and finally i was looking at a facet low pressure fuel pump and saw that there is a built in pressure relief so im gonna go with that


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 Post subject: Re: From carbs to efi
PostPosted: July 8, 2019, 6:32 pm 
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A pump that turns all the time with a return or internal relief (which the carter has) is more reliable than a pump that starts and stops regularly but any should last a long time. Solenoid "box" pumps like the facet vibrate and shake so it needs to be isolated with a rubber mount to keep down the noise but that will work fine.

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