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Fuel bladder/I V bag plumbing

Old 11-22-2021, 11:51 AM
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CptnCR
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Question Fuel bladder/I V bag plumbing

Hello, I'm installing a fuel bag in my 43" V hull, powered by a 26cc Zenoah. I've got everything done, but the plumbing. Do I need a fuel pump now? I was under the impression that it would not, but then started seeing mixed answers to this question. And also would like to know about the primer/return line's placement. Any help would be greatly appreciated and thank you.
Old 11-22-2021, 02:27 PM
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A Zen has a pump as part of the carb so no, an additional pump isn't needed.
As for line placement, I'll leave that to someone that runs a "V" hull
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Old 11-22-2021, 08:16 PM
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So can I do away with the primer bulb. If there is no return line going into the bag. Well there are two connections on the bag ,but I thought one went to the filler plug. Thanks for replying though.
Old 11-23-2021, 06:44 AM
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The integral pump will pull more fuel than the engine and carb actually can use so, unless you want to waste a lot of fuel that will be dumped into the bottom of the boat, you will need the return line. This is the big difference between a gas and nitro engine. In a nitro engine, the needle valve restricts the fuel flow into the carb to just what the engine can actually use, the fuel being pushed to the carb by exhaust pressure. The Zenoah integral pump actually overloads the carb with pressurized fuel. This pressurized fuel is then "metered" by the needle valve as it only allows through the amount of fuel the engine can actually use. Any excess fuel is then returned to the bag for reuse. This is the same principle used in a fuel injected engine used in your car or truck, but not in a carb equipped engine. That's a whole different can of worms
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Old 11-23-2021, 09:31 AM
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That helps a lot, thank you Hydro Junkie. So I can route my filler port line to the return line from the carb and I should be fine on that.
Old 11-23-2021, 06:27 PM
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Plug one of the outlets on your IV bag, you only need one. I run one line from the bag to the carb, with a T in the middle. On the third leg of the T, I add a short piece of tubing and a fuel dot. Easy peasy.

With that said, I usually find hard tanks easier to fill and use.
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Old 11-24-2021, 08:31 AM
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Originally Posted by JS440 View Post
Plug one of the outlets on your IV bag, you only need one. I run one line from the bag to the carb, with a T in the middle. On the third leg of the T, I add a short piece of tubing and a fuel dot. Easy peasy.

With that said, I usually find hard tanks easier to fill and use.
When I bought my boat it had a tank in it, a big tank, and someone suggested a fuel bag to reduce weight. I thought I'd try it out.
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Old 11-24-2021, 08:38 AM
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It will be a bit lighter, those tanks you have shown are also a bit heavier than most. IV bags have their place, and work fine, I just find them to be more of a PITA than they're worth for me personally. You have to be sure to burp ALL of the air out of your bag before you run though, which usually involves standing the boat on its bow, allowing the air to rise as you squeeze the bag, then capping it back off... it can be a bit tricky to get used to, and it's the main reason I've swapped my boats running bags back over to hard tanks.
Old 11-24-2021, 09:29 AM
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A carb with a primer bulb really doesn't need a return line fitted to it as spit out much fuel. Some IV bags are set up with 2 hookups but you only need one. I use the Zippkits bags myself which only have one.
Old 11-24-2021, 11:14 AM
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Originally Posted by JS440 View Post
It will be a bit lighter, those tanks you have shown are also a bit heavier than most. IV bags have their place, and work fine, I just find them to be more of a PITA than they're worth for me personally. You have to be sure to burp ALL of the air out of your bag before you run though, which usually involves standing the boat on its bow, allowing the air to rise as you squeeze the bag, then capping it back off... it can be a bit tricky to get used to, and it's the main reason I've swapped my boats running bags back over to hard tanks.
This is my first gas boat and my first v-bottom also. I had a couple outriggers id built to run electric. This might be interesting to see how it runs. The hydros can be fun they don't do chopy water.
Old 11-26-2021, 05:16 PM
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Originally Posted by Ron Olson View Post
A carb with a primer bulb really doesn't need a return line fitted to it as spit out much fuel. Some IV bags are set up with 2 hookups but you only need one. I use the Zippkits bags myself which only have one.
Ok, so my bag i bought from gizmomotors has two ports on one end and I think I figured away to keep bubble from sucking down in to the bag when I'm filling it.(I just have a homemade squirtbottle). I put a check valve in line from the filler cap to the bag on one port and the other to the carb and no return. The line the was on the primer is still hooked up with a pug in it. After I filled up the bag I just popped out the plug and pumped the primer and the residual air bleed out and its now primed.
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