External Fuel Pumps

[paczowski123]

Can someone explain why so many use the external fuel pumps on their larger engines? Is this a necessity? Advantages/disadvantages?

 

[txsuperjetfreak96]

Would b nice to know as well, I always assumed it pushed the fuel to the carbs quicker

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[paczowski123]

I found one very vague post where some claimed it helps seperate the engine vibration from the pumps increasing efficiency, and one that said it helps engines that don't get enough fuel from the internal pump. But to me, I look at having two pumps is better then one? So is the external that much more efficient?

 

[jo5hi3]

I remember talking with ed about this. I think he said that the external pump, pumps twice as much fuel as the two carb mounted pumps. Also when it comes to rebuild time its only one pump to rebuild instead of two.

 

[paczowski123]

Interesting..its just strange, you see some running them with big engines and others with similar, even bigger setups with internal pumps.

 

[jo5hi3]

Ed claims there is an improvement when switching from the carb mounted pumps to the external pump. I'm running an 1105 with 49's and carb mounted pumps.

 

[paczowski123]

Exactly, and you'll see people with 850's or smaller running external. Maybe it's just what they buy or find for sale.

 

[jo5hi3]

True. I think many people buy fs carbs used because of the price. I think mine were $1600 after shipping, if you went with block offs and external pump that just adds to the bill.

 

[paczowski123]

Man, I need your job.

 

[jo5hi3]

Hhahahaha, thats just what you think......

 

[speedysprocket]

You ensure you get the same fuel pressure at both carbs as well when you use one common pump instead of two independent ones. Should make tuning that much more accurate and easier...

 

[paczowski123]

But isn't there more modifying the return lines and everything with restrictors and stuff to make sure you get equal fuel pressure?

 

[jo5hi3]

You ensure you get the same fuel pressure at both carbs as well when you use one common pump instead of two independent ones. Should make tuning that much more accurate and easier...

I have always been told running them to a Y on the return side with a return jet made both carbs have equal fuel pressure. I guess if they are both fed by one pump and its low then both carbs will have low pressure, same if its high..... I have never had an issue dialing in dual pump carbs, but at the same time I have never worked with an external pump setup.

 

[paczowski123]

I guess if one pump is weaker then the other one might not create as much as the other?

 

[jo5hi3]

That's what the return jet is supposed to equalize, and also create fuel pressure for the carbs to operate properly. Also that's why running the return lines to a Y or a T is supposed to help this. A Y is less restrictive and allows both to flow more equal.

 

[paczowski123]

I gotcha, so if one carb is slower than the other, the restriction allows it to catch up.

 

[jo5hi3]

I would think so, but that's just a theory, I have never actually checked pressure to see.

 

[Proformance1]

Ed is one of the guys that always recomends the separate FP. If you are looking at the throry talk to him, if not you can look up the fuel of the 46's pumps and the remote pump and see that the remote pumps more fuel. Pressure should not shcnage at as all the restrictor is the same. I personally feel that the larger fuel pump is more geared towards race, I ahve had no issues at all witht he individual pumps, that being said all major competitors use the remote pump. With that for the rest of us, does it really matter? Forget the minute details, 100% race gas, 245psi, 38 deg timing, 162 mm pumps, etc. Do you really need that to go out and ride with your buddies? Sure it makes for good reading, and discussions, and if you are one of those guys that has to have the 2000HP car in the neighborhood, but in reality we are brapping around 90% of the time and trying some tricks. Concentrate on the riding, that is key.

To answer the question: advantage fuel delivery, possible gains. disadvantage: cost, pumpbing changes. Duals require a 5/16" feed line, mnost tanks are set for 1/4".

 

[paczowski123]

To answer the question: advantage fuel delivery, possible gains. disadvantage: cost, pumpbing changes. Duals require a 5/16" feed line, mnost tanks are set for 1/4".[/QUOTE]

A bit confused here, what do you mean duals require 5/16" line?

Thanks for the response, I also saw it as an unnecessary nuisance, but it just seems like I am seeing it more and more.

 

[Proformance1]

The single pump that feeds a dual carb motor requires a 5/16" line from the tank to the pump. One side note is that if you have a single pulse case and dont want to drill for a second fitting, this is a great solution.