Electric fuel pump to prime carbs

Dick Steinkamp

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bavbob

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Exactly, if in parallel and no valve, gas will make a loop from tank to pump and back to tank. Pump will be pulling from the tank and pushing toward the tank simultaneously...........not good.
 

bluecoupe30!

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I have a pair of Weber 32/36s on my Coupe. I lived through the days of hard starting, after the car had sat a few weeks. Installed one of those check valves and it really helped, but a big piece of the puzzle was a replacement battery. Need full cranking power to keep trying and then get started. I would recharge other battery and if temperatures were warm, starting was easy, but as soon as temps got colder, the battery really struggled. At least a new battery is simple. Mike
 

JFENG

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jmackro

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It could be my wording is misleading.

Without the one-way valve, the fuel coming out of the pump might meet too much resistance to go toward the carbs and make a right turn and return to the inlet of the pump.
Dick:

Hmm. It's probably not worth beating this to death, but I'm still not seeing the possibility of a return path, unless the two pumps are in parallel. When you wrote "the fuel coming out of the pump might meet too much resistance" did you mean the fuel coming out of the electric pump might meet too much resistance from the mechanic pump? But if so, what is that return path (again, assuming the two pumps are in parallel)?

Incidentally, I saw your Bavaria at Legends last month and wanted to meet you. But I was only there a short time and we just didn't connect. The Bavaria is just as impressive in person as your photos have indicated.

Thanks for the links to the one-way valves on ebay and Amazon. Duh! I should have known that everything is on ebay, Amazon, or both.

JFENTG said:
You probably stopped having keggers a few years ago and have forgotten:

I was always on the consuming end of the kegger thing but not on the plumbing side. Upon checking Amazon, they too have some 5/16", three-way fittings, though they're in more of a "Y" configuration:


51StU-zZbUS._AC_SY355_.jpg


See: https://www.amazon.com/ANPTGHT-Fitting-Stainless-Splicer-Household/dp/B097JGVQS4/ref=sr_1_16?crid=22KY4FXG5FV0S&keywords=Fitting,+Y,+Stainless,+5/16"+Barb&qid=1663520547&sprefix=fitting,+y,+stainless,+5/16+barb,aps,124&sr=8-16&th=1
 
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Dick Steinkamp

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Jay
Sorry I missed you at Legends. Hopefully we'll connect in person one of these days.

I'll take another shot at explaining the system that Pierburg recommends...

"When you wrote "the fuel coming out of the pump might meet too much resistance" did you mean the fuel coming out of the electric pump might meet too much resistance from the mechanic pump?"

Yes

Screen Shot 2022-09-16 at 11.07.48 AM.png


In the diagram, 03 represents the new electric pump to be used what Pierburg calls a "pre-feeder pump". One that is used to refill the carb bowls prior to starting, but not while the engine is running. 06 represents the stock fuel pump...in my case it is the stock mechanical pump.

07 is the bypass line around the new electric pump. 05 is a one way valve that will only allow fuel to flow left to right in the bypass line. The bypass line is there so that if the stock pump can't pull fuel through the new electric pump when the engine is running and the new electric pump isn't, that there will be a path for the fuel from the tank to the stock pump.

The 05 one way valve is there in the 07 line to insure that when operating only the new electric pump prior to engine run, that the fuel being pumped by it doesn't take the path of least resistance and turn right when it comes out of the new pump at 07 and return to the tank/new pump instead of going straight ahead to (and through) the stock pump.

I hope that helps.
 

jmackro

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07 is the bypass line around the new electric pump. 05 is a one way valve that will only allow fuel to flow left to right in the bypass line. The bypass line is there so that if the stock pump can't pull fuel through the new electric pump when the engine is running and the new electric pump isn't, that there will be a path for the fuel from the tank to the stock pump. The 05 one way valve is there in the 07 line to insure that when operating only the new electric pump prior to engine run, that the fuel being pumped by it doesn't take the path of least resistance and turn right when it comes out of the new pump at 07 and return to the tank/new pump instead of going straight ahead to (and through) the stock pump.

Oh yea, sure, I get that. Certainly, if you put a hose without a one-way valve in parallel with pump 03, the fuel would just go around in a circle. But that would be such an illogical thing to do, that I guess I didn't even consider it. I thought you (and others) were referring to a system with the two pumps in series, without the bypass (e.g., no components 05 & 07) and still saw some path for fuel to run back to the tank.

OK, thanks for clarifying.

Jay
 

Dick Steinkamp

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Epilog....

I was a little concerned that Rob didn't have success with the Pierburg pump without a bypass hose and that Pierburg recommends a bypass hose if their product is used as a "pre-feeder" pump even though Dan and Chris did have success using the Pierburg without a bypass. So I tried to do some research to determine which pump(s) definitely can suck through by the OE pump and could be mounted above the tank.. I did not want to plumb in a bypass hose with the accompanying additional connections and I didn't want to put the pump under the car.

Those two variables (suck through and work above the fuel) are not spelled out in any of the product literature I could find. I ended up reading a bunch of Amazon reviews to find that info and did find one that satisfied both. It happened to be the cheapest pump of all those offered on Amazon :)


Screen Shot 2022-09-18 at 3.13.15 PM.png


I ordered it Saturday and received it today. I sucked on the outlet tube and there was zero resistance to air flow. I blew into it and confirmed it had a built in check valve. So I installed it.

IMG_8541.JPG


I installed an in line low amperage fuse like Dan Suggested. I used a tank hold down bolt for the ground. I used power from the rear window defroster like Rob and others have done.

Works great! (so far)

This pump is bigger around than the Pierburg and I installed it in my E3, so check the dimensions before trying it in an E9 since the required clearance may be different on an E9.
 

gwittman

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I have used a priming electric pump for over 10 years inline in series with no problems. I can't remember what kind it is but it was not expensive.

I remember one very hot day after driving a while and parking for a bit, when I restarted and began to drive away, the engine started misfiring. Thinking it might be related to vapor lock, I turned on the electric fuel pump. The misfiring ceased and I continued on. After five minutes or so I turned off the electric fuel pump and the engine continued to run well. That never happened before or after and I hope it continues that way.

Not that it makes any difference, mine is under the hood for ease of wiring.
 

Ohmess

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Following Stevehose's recommendation, I'm using a revolution electronics fuel pump controller that pumps 3 seconds of fuel when I turn the key to fill the bowls before starting the car. The controller also contains a cut off that shuts down the pump if the engine is not running. I'm using this to control the same pump Chris pictured in his NK.

I've posted about this a couple of times before. See here: https://e9coupe.com/forum/threads/inline-electric-fuel-pump-what’s-the-best-option.37654/post-320104 and here: https://e9coupe.com/forum/threads/final-word-on-electric-fuel-pump-for-carbs.22574/post-165264
 

JFENG

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Is 3 seconds long enough? On my old British car, I let the electronic pump run until the sound changes, indicating the float bowl needles have closed. Then I hit the button and it starts. If Inhaven driven the car in 3 months, it takes maybe 5 seconds for the pump sound to change. i guess with this controller you just cycle thee key several times, right?
 

Ohmess

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Is 3 seconds long enough? On my old British car, I let the electronic pump run until the sound changes, indicating the float bowl needles have closed. Then I hit the button and it starts. If Inhaven driven the car in 3 months, it takes maybe 5 seconds for the pump sound to change. i guess with this controller you just cycle thee key several times, right?
Not sure as I don't usually go three months without running my car (unless I've torn it apart). I think three seconds was based on fairly regular usage. That said, it is not hard to cycle the ignition key and get another three seconds.
 
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