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Siphoning tanks

Discussion in 'Carb Fuel Systems' started by jphelzer, Jun 18, 2021.

  1. jphelzer

    jphelzer Junior Member

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    Truck Year:
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    Engine Size:
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    Hi All,

    I searched but couldn't find anything on this topic.

    I recently bought my 1977 K25. I got it for a steal. It's been sitting for 8+ years but was started a few times a year by the previous owner..

    Before trying to start it, I changed the oil, belts, etc. I ran a line from the fuel pump to an external can. The truck started and ran great!

    Ideally, I'd like to drop the tanks and clean them, but I really don't have the space and means to do that. So I bought a hand pump and attempted to siphon the fuel though the filler neck.

    The line went down about 14-16" into the tank, but won't siphon and the hose is dry. Is this not the proper method? Is there a better way?

    The fuel guage works and the tank selector switch works as well. One tank shows less than 14 and the other shows 3/4. The truck will run forever on an external tank and the filter is clear (and new)

    What am I missing? Thank you in advance.

    John
     
  2. 75gmck25

    75gmck25 Full Access Member

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    5.7
    I've tried running a siphon hose down the filler pipe, but never got it to snake around far enough to get into the tank. And I never figured out why it was so difficult.

    Another option I've considered is to disconnect each 3/8" supply hose where there are connected to the fuel tank solenoid under the truck, and see if I could get it to draw fuel from there. You will have some resistance from the sock on the fuel pickup in the tank, but it might work.

    I've also ended up dropping the tank when about 1/4 full of fuel and its not really that hard to handle.
    - Put a wide board (1x8 or 1x10) under the tank and then a hydraulic floor jack under the board.
    - Remove the four bolts for each tank bracket and wiggle the tank until it is free.
    - Remove the clamps where the rubber lines connect to the fuel supply and return on the solenoid, and the T for the vent line.
    - Then remove the clamp that holds the rubber lines where they go up and over the cross brace.
    - Then slowly lower the tank and guide the lines up and over the brace.
     
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  3. Grit dog

    Grit dog Full Access Member

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    Easiest thing would be to buy a cheap electric fuel pump and hook it up by the fuel pump, imo.
    Fwiw, I pulled one original 1986 tank off mine. Tank had some rust holes. Inside was surprisingly clean and the pickup and sock was clean too.
    If I was going to drop tanks, imo, removing the bed would be easiest and then you can easily clean everything up replace lines etc whatever need to be done.
     
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  4. jphelzer

    jphelzer Junior Member

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    Thank you for the suggestions! I'll update the thread soon.
     
  5. Bextreme04

    Bextreme04 Full Access Member

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    When I bought my '80 K25 that had been sitting for 12 years, I replaced the whole fuel system. New pump, new rubber hoses, new sending units, and rebuilt the carb. I dropped both tanks, cleaned them out, and replaced the sending units in an afternoon. You just need a floor jack, pliers, and a 9/16 socket. I just removed the tanks and holding brackets all at once and lowered the entire thing down until I could get the last of the fuel lines disconnected. It is easier, if your bed bolts aren't completely rusted, to just remove the bed bolts and slide the bed back on the frame about a foot. You can then remove the sending unit and look in without even removing the tank and see if you need to go further. My tanks looked spotless while the sending units were completely rusted up and trashed.
     
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  6. SirRobyn0

    SirRobyn0 Full Access Member

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    We do quite a bit of older / classic work at the shop and this is the method we use. But if at all possible we pull the tanks. The reason being is like in your case 8 year old fuel, you won't get quite all of it out the suction hose, and it's not uncommon for the sock in the tank to be plugged with varnish. Plus there could be rust. Pulling the tank gives you the opportunity to check all that stuff inspect the sending unit ect.

    Since that's not practical for you I'd strongly recommend after you have all the old yucky gas out, put a couple gallons in the tank slosh it as best you can rocking the truck and then suck that out. Then I'd run some marvel mystery oil in the first couple of tanks, the reason being is that MM has great lubricating properties and will help out that old sending unit which might not be the best. It's also coat anything rusty in there and hopefully reduce it.
     
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  7. jphelzer

    jphelzer Junior Member

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    Thank you, everyone. I ordered a cheap fuel pump and I'll test it out tomorrow.

    It's a CA truck with almost no rust so I hope the tanks are OK. I'll find out! :)
     
  8. 75gmck25

    75gmck25 Full Access Member

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    The tanks may be relatively clean inside, but the sweep arms on the sending units really get rusted when they are exposed to air in an empty tank.

    As the float moves up and down it sweeps a metal arm up and down a metal variable resistance strip on the sending unit. The metal strip tarnishes when it’s not immersed in gas, so the sweep arm doesn’t make good contact, and you don’t get accurate gauge readings .
     
  9. SirRobyn0

    SirRobyn0 Full Access Member

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  10. jphelzer

    jphelzer Junior Member

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    Sorry, I got busy and haven't been back.

    I used an electric fuel pump and drained 2-3 gallons from the left tank. It was pretty clear with no sediment or particles. I put a gallon of fresh fuel in, connected the truck's fuel pump to an external 1-gallon can and drove it around for a while.

    I emptied it again and got a 1 gallon of clean fuel. So I feel confident that the tanks are good. I'll do the right next, but the gauge shows it has 3/4 tank and I need to find a place to store the fuel until I can recycle it.

    Huge thank yous to everyone that replied! I can't wait to keep working on my K25 and getting help with the awesome people here.

    John
     
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  11. Raider L

    Raider L Full Access Member

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    @SirRobyn0,

    Is that the reason why I used to be told by people to always keep a 1/2 a tank full of gas? To keep things from rusting in the tank? They never said anything about rust, just the gas.
     
  12. SirRobyn0

    SirRobyn0 Full Access Member

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    @Raider L I've heard a lot of theory's on that stuff. That's one. Personally when I'm not going to be using a rig for a while I fill it full before parking it. In a worst case scenario I'll have a tank of bad gas but it seems like a larger quantity of gas will last longer in a tank than a small amount. I think part of that is when there isn't much fuel in a tank there is a lot of air. Where there is air there is moisture, which at least equals potential rust. On vehicles I drive regularly I go ahead and run them full to empty, or should I say full to low. No harm in that at all. I use to have one moron, a mechanic no less that insisted no vehicle should ever be run lower than 1/2 tank to avoid sucking up dirt and debris on the bottom of the tank. He talked as if he thought the fuel pickup floated on the top of the gas, like the level sender float does! Did he not know the pickup tube sucks from the same spot no matter the level of the fuel. I really don't bank much stock in that stuff other than like I said when I'm going to be parking a rig for a while.

    As a side note if you didn't know at a gas station each pump and each grade has a huge spin on filter that looks like a giant oil filter under the lower cover below the handle. At the service station I use to manage our pumps took filters about 18" long by maybe 6" across. Big filters! So each pump had three of these one for each grade and each filter was about $60. To do all the pumps it was nearly $1400 in filters and we did them every 6 months, I insisted on it and that is industry standard pretty much depending on the volume pumped. My point, one of the things that will cause gas pumps to pump slow are plugged filters. So station owners / companies will try to cheap out on filters. Other things can cause the pumps to run slow, but if your at a station and experience slow pumping you may not be getting the cleanest gas.
     
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  13. DoubleDingo

    DoubleDingo When In Doubt, Throttle Out

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    Put in a can of berrymans b12, and top it off with fresh fuel. Do this three times minimum and you'll be fine. If you have dual tanks, do it to both at the same time. When I bought my '81 the PO said the passenger tank was no good so he carried a 5 gallon can of gas everywhere he went with that truck. I filled the passenger tank with fuel, no additive, and it ran just fine. Drove the entire tank to empty without any issues. But I did add the additives afterwards on the next fill-up, and have done so a few other times. Before I run that truck again, I will add some additive to the tanks and fill them up, and all will be fine. It's also good practice to have an auxiliary in-line filter downstream from the valve on dual tank systems, or just mounted on the passenger side frame on single tank systems to catch any rogue debris from the tanks before it makes it to the fuel pump or carburetor. Easy to change out, and good insurance of a clean fuel system.
     
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  14. Rusty Nail

    Rusty Nail Victim of Culture

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  15. shiftpro

    shiftpro Full Access Member

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