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corradolvr
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PostPosted: Sun Aug 29, 2010 7:26 pm    Post subject: Dual Carb Plumbing Reply with quote

Got Dual IDF Weber 40s and I'm not really sure exactly how to plumb them. I thought I could just use a "T" of the output from the fuel pump then run a line up to each one, but I don't want it to look sloppy. Does anyone have any pictures of there dual carb plumbing, or advice?
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PostPosted: Sun Aug 29, 2010 7:29 pm    Post subject: Reply with quote

i run one out of the pump and have a t behind the dog house and they only place u really see my fuel lines is where they go to the carbs

im running dell 40's
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corradolvr
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PostPosted: Sun Aug 29, 2010 7:41 pm    Post subject: Reply with quote

Are you running a stock mechanical pump? Line in to the pump, then a line to behind the doghouse, then a "T" back there?
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PostPosted: Sun Aug 29, 2010 8:03 pm    Post subject: Reply with quote

oops should have given more details

my cell is in the back seat then it goes out to my holly red pump then under the package tray to a pressure regulator then filter then the T going to each carb
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PostPosted: Sun Aug 29, 2010 8:08 pm    Post subject: Reply with quote

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corradolvr
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PostPosted: Sun Aug 29, 2010 9:12 pm    Post subject: Reply with quote

Nice work on that plumbing. I might borrow that idea if you don't mind.
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PostPosted: Sun Aug 29, 2010 9:31 pm    Post subject: Reply with quote

Glenn wrote:
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mine is very similar but i used braided line
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PostPosted: Mon Aug 30, 2010 2:34 pm    Post subject: Reply with quote

Here's another. I'm running IDFs now with this setup:

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PostPosted: Mon Aug 30, 2010 11:09 pm    Post subject: Reply with quote

One small detail is to make the hose lengths equal to each carb from the tee. Under hard acceleration when both inlet needles are open fuel will flow to the path of least resistance. I had my 2276 plumbed like Glenn's and couldn't figure out why the plug readings were different from side to side. I changed the fuel hose to equal length and the plugs became identical.
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PostPosted: Mon Aug 30, 2010 11:27 pm    Post subject: Reply with quote

this is what I got so far
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PostPosted: Tue Aug 31, 2010 3:40 am    Post subject: Reply with quote

Scott Gilbert wrote:
One small detail is to make the hose lengths equal to each carb from the tee. Under hard acceleration when both inlet needles are open fuel will flow to the path of least resistance. I had my 2276 plumbed like Glenn's and couldn't figure out why the plug readings were different from side to side. I changed the fuel hose to equal length and the plugs became identical.

Weird... i've not seen a difference in the 8000+ miles i've driven.
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Scott Gilbert
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PostPosted: Tue Aug 31, 2010 10:35 am    Post subject: Reply with quote

It is only under hard acceleration when both float bowls are requiring a lot of fuel. Depends on needle & seat size (3 mm in my case). It would never be a problem with normal street driving. But most of us with dual carbs like to accelate hard on the street from time to time.

Best way to test it is to clean your plugs and drag race all day! Or put an O2 on each side and datalog.

Then again it is just easier to use 6" more of hose and put the tee in the middle.

[quote="Glenn"][quote]
Weird... i've not seen a difference in the 8000+ miles i've driven.[/quote]
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PostPosted: Tue Aug 31, 2010 11:01 am    Post subject: Reply with quote

For a dead stop and shifting at 7600rpm I have no problem running up to 107mph where I shift into 5th and its still pulling.

While I'm not doing that everyday I do drive the engine hard at times and the last time I pulled the plugs to check them they were pretty even from cylinder to cylinder. And that's with 8000+ miles on them.

BTW.. ever see how they plumb the 4 IDAs on a Cobra?
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PostPosted: Tue Aug 31, 2010 12:12 pm    Post subject: Reply with quote

It probably makes more of a difference depending on the output of the fuel pump.

I think the cobra uses a high output pump and those lines are rather short.
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PostPosted: Tue Aug 31, 2010 2:32 pm    Post subject: Reply with quote

Glenn,
Iím just saying what I have seen in my case. Take it for what it is worth. Donít know why you wouldnít think that putting the tee in the middle is a good idea. Look at the fuel flow and pressure as it travels through the fuel line. Fuel pressure is only 3.5 psi to begin with, what is going to happen when the 1st carb N/S is completely open allowing all available gas in? Pressure drop to the 2nd carb. 1st carb is receiving more psi because it is closer to the pump. If you have a tee and equal length fuel hoses that issue is eliminated.

The dynamics of the engine are different under hard acceleration than when cruising. My case was exactly the same as you. My plug readings looked great because I used the car on the street mostly, but when drag racing it didnít pull as hard as I thought it should in 4th gear. I found that in 4th gear the 1-2 side carb was running out of gas. I changed the fuel line, it solved the problem, plugs looked great, and the car went faster. Pulled hard all the way through 4th gear. Went faster on the street too! My stock weight street car would run 11.70s @ 115mph with a 2276 & IDAs. I shifted at 8K without taking my foot off the gas.

Maybe they plumbed IDAs on a Cobra like that back in the day, but that doesnít mean it was right.
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PostPosted: Tue Aug 31, 2010 2:36 pm    Post subject: Reply with quote

Scott Gilbert wrote:
Maybe they plumbed IDAs on a Cobra like that back in the day, but that doesnít mean it was right.

I think Carol Shelby knows a few things about building hi-po engines.

Anyway... we're splitting hairs when talking about street engines.
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PostPosted: Tue Aug 31, 2010 5:55 pm    Post subject: Reply with quote

best pic. i have right now, electric fuel pump up front.
equal length lines from the tee.

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PostPosted: Tue Aug 31, 2010 11:48 pm    Post subject: Reply with quote

That got complicated. Well If they are tuned with different lengths shouldn't that accommodate the length difference? in a pressure system with relatively low changes in height, a fluid less dense than water, and low pipe friction factor I wouldn't think it wouldn't matter a whole lot.
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PostPosted: Wed Sep 01, 2010 5:24 am    Post subject: Reply with quote

I think it would only be an issue when you are close to exceeding the ability of the fuel pump. If you have more than enough gas being pushed (like FI with a return line) then this won't be an issue, but if you are having trouble keeping the bowl full, then it would be.
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PostPosted: Wed Sep 01, 2010 7:26 am    Post subject: Reply with quote

I friend that races Super Stock Class bought a new to him drag car, changed how the fuel lines were run and picked up 0.010 in the 1/4. Doesn't sound like much, but it put him to the point of just under the record for that class.

I cannot see it making any difference on a street engine, I would think the tickets from so much wide open throttle use would be of a bigger concern. If your leaning out one side, your fuel pump is not adequate.
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