I have 86 f150 xlt lariat when running 1st tank it drives fine but as soon as switched to 2nd tank it starts to spit and sputters and loses power any thoughts help please

 

Defective dash switch or faulty lift pump. Best guesses.

 

Have a look at the link in my signature.

 

You might also consider the posibility that the 2nd tank has debris clogging the fuel sock.The fuel selector valve on the drivers side rail behind the cab is easy to replace and are available at your local auto parts store.

You might also look at the rubber hose running from the fuel tak and dowwn the rail to the fuel selector valve as they do corrode they are subject to aging and oxidation.I had one once that looked good but on start up it caved in on it self and closed off the fuel feed from the tank.simple replace but difficult to find.Some times like on my 82 it is easyer to just replace all hose from the tanks up to the motor.Good luck with it.