The wiper hoses I've had are pretty small. It can not possibly affect the motor when plugged. It's plugged when wiper is off. The motor gets it's air from a huge opening called the carburetor. Plugging the vacuum port at manifold would increase venturi flow. You are not getting enough gas/idle circuit. Carb problems as said already. Motors surge/stumble because of vacuum leaks not plugged wiper hoses. Are you plugging it right at the manifold? Is your fuel pump also a wiper pump?
Is your choke stuck closed? Do you have a small "Hot Rod" air cleaner, Is your air cleaner plugged?
If all you are asking is why it won't go forward in idle with a standard transmission, set the idle up to specs. Check the clutch. Be in first gear. Is this a 4 speed with granny low (compound low)? or a 3 speed or what?
Believe it or not, it does take practice if this truck is new to you or has new drivetrain components.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
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