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'87 w/dual tank converted to carb prob

Discussion in 'Chevy Trucks' started by 400hp408sb, Oct 8, 2003.

  1. 400hp408sb

    400hp408sb Junior Member
    from Maine
    Messages: 25

    I'm not sure if anyone will be able to answer this but I'm sure someone else has done this same thing. I have an '87 with factory dual tanks and the engine was a 350 TBI. I took the engine out and put in a 400 with a carb on it. I am using a mechanical fuel pump on the motor and left the two original electric pumps in the tanks. The mechanical pump just sucks right through the electric ones. My problem is this. My tank switch no longer works. I have been stuck using only one tank since I have done the swap. Should I go buy a switching valve made for a carb setup that runs about 70 bucks. Or is it as simple as just getting a certain wire constant power that is now not working since the computer is not in the truck. I have put the computer back in just to see if it enabled my switch to work again and it does not. There appears to be three or four wires that goes out of the firewall on drivers side along the frame and then cuts over to the switching valve on the passenger side. Any thoughts or help on how to get my auxilary tank working again would be very helpfull.
  2. 75gmck25

    75gmck25 Senior Member
    Messages: 119

    Take a look at the wiring diagram I posted in the other thread about dual tanks. I don't know how the TBI switch and valve are wired, but you might be able to make some changes and get it to work with your system. However, it seems like the valve itself might be different with TBI.

    You can find the carbureted truck dual tank valve and switch on quite a few junked trucks. All the switch does is apply 12 volts to the valve selenoid when you switch to the aux tank, while at the same time switching the sending unit-to-gauge wire from one tank to the other. The switch is a standard dual pole, dual throw switch.

  3. Rick Loncosky

    Rick Loncosky Senior Member
    from 17557
    Messages: 102

    Why don't you use the electric pumps in the tanks and get a small pressure regulator to cut the pressure down to 5 -7 psi. Then you could block off the mechanical pump. Maybe with the pumps working the switching valve might work.:drinkup: