Fuel petcock 1987 brand new

[loquito]

It seems like the petcock won't open and let the fuel flow. Can someone
Tell me what the wires coming out of the actual petcock
Are for?

[weymouth399]

Reserve switch.
It needs vacum to work or put in the prime position, but be warned it will come out then.

Bob W

[loquito]

I hooked it up to vacume still nothing, what is the prime
Position?

[moparman70]

If you take the plate apart you will see a black membrane that has a spring on one side and a O-ring on the other side.  When you turn the motor on the vacuum sucks the membrane out/plunger with O-ring with it and allows the gas to flow.  I won't get into the reserve function - its weird / nifty how it works depending on your perspective.

If you have the gas line off and engine off there should be no flow.( gas line off just to see if you have flow ...you may want to hook a temporary line up and route to a bucket with the tank in position just to monitor flow)  

Most have the problem where the O-ring is either worn or cracked and does not seal when off and so there is always leakage.   Turning on the engine with vacuum line should result in lots of flow.  If not you probably have a cracked or hole in the membrane so when  you are pulling vacuum there is a leak and it doesn't suck the plunger with the O-ring in to allow the gas to flow.

If you have lots of fuel and your reserve light is not on the switch should be in the normal position ( back part down).  But if the above doesn't work make sure the wires are hooked up and push the reserve switch so the back part is up ( some machines you will see a sticker once you depress the switch that says reserve.)  It is worth a try in reserve to see if the flow starts.   The tank should be level for all of the above as the fuel flow is by gravity.

hope it helps --- do some research on this subject ... there is lots of info on 86-87 petcocks