So you installed a Weldtron board you bought from Weld-Mart. (Lincoln OEM board M13708 is $89) If the new board installation did not fix your problem I would say that wasn't the problem in the first place. What is the code of your machine? Do you have engine protection on your machine? The pc board has mounting stand offs. I would make sure the metal they are mounted on is clean (this way the board has a good ground).

12 volts DC to the solenoid pulls in the plunger and idles the machine down. The loss (or time delay grounding of this voltage by the pc board) of this 12vdc releases the plunger in the solenoid and idles your machine up. **Do not have machine running while doing the following----The wires to the solenoid have numbers on them 56 and 57. Locate 56 and disconnect it. Using a battery connect the positive lead to the stud you just removed wire 56 from. THE PLUNGER SHOULD PULL IN (IDLE DOWN). When you remove the 12v the plunger will release (idle up). Reconnect wire 56.**** If the solenoid does not operate properly check for mechanical restriction in the linkage or a missing spring. The solenoid coil resistance is 9 ohms
You need to look for faulty or loose connections in your wiring. Look for missing or loose parts to your solenoid, such as linkage and springs. It is not uncommon for the linkage arm to come loose of the injector. Or for the spring to fall off. Wire 56 should be the bottom wire on the solenoid, it also goes to your idle switch and "Y" termianl of the board.