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Everybody had a crack at this problem, another thing would check is these engines sometimes have a primary fuel filter inside the tank itself. Drain the fuel and gently blow compressed air back through fuel line towards tank then rinse the tank out with fuel, refill and try run engine again
The small diameter line out of fuel tank (has filter in-tank on end) connects directly to the side of the carburetor that has the fuel pump....that is the cover without the hole in it. Other larger diameter fuel line out of tank connects to the longer nipple on the external purge/primer bulb. The bulb "pulls" fresh fuel from the fuel tank to the carb and then out of the carb to itself, where it then "pushes" any air/old fuel back into the fuel tank. The remaining larger diameter fuel line in this setup goes from the metering chamber (has cover with writing on it and a vent-hole) side of the carburetor to the smaller nipple on the purge/primer bulb. Again, on the primer bulb, the longer nipple has a line going directly from it to the tank. This is the return line. The shorter nipple on the bub has a line from it going to the metering chamber side of the carb. If the purge/primer bulb is on top of the carb...small line from carb body to small hole in tank with filter. Larger diameter line goes from the bulb on the fuel pump side of the carb to the larger hole in the fuel tank where sometimes the line is held in place with a nylon nipple connector that keeps the line from pulling out of the tank. Otherwise, the line should enter the tank for about 1/2" or so.
How do the fuel lines hook up to the carburetor, huh? Well...it's not too complicated. Small diameter line coming out of fuel tank goes directly to the carb on the fuel pump end..(end opposite the one with hole in the cover). The larger line coming out of the fuel tank goes to the longer nipple on the purge/primer bulb. The other line coming off of the carburetor (on the end with the hole in the cover) goes to the shorter nipple on the purge/primer bulb. The purge bulb "pulls" air and old fuel out of the carb thus allowing fresh fuel to flow in from the fuel tank and then it "pushes" this mixture of air/old fuel back to the fuel tank.
Presuming the primer bulb is on top of the carb....Fuel filter line out of gas tank goes to the lower part if carburetor body. The other line (normally larger in size) coming out of the fuel tank goes to the primer bulb outlet on the top of carb.
If the primer/purge bulb is not on the carb, things are a little different. The fuel filter line out of the tank still goes directly to the carb, as the bulb will pull old fuel/air out of the carb allowing fresh fuel to flow in and pushes old fuel/air back to the fuel tank.
Fresh fuel in, old fuel out of the carb...you can hook up a piece of fuel line to the bulb and tell which one is pulling and which one is pushing..or depress it with your fingers on it...either way you can tell.
This is the same problem I have with a Mac 3200. I have: (1) A line from the primer bulb to the front port on the carburator. (2) line from fuel tank, with attached fuel filter, to the other primer bulb port. (3) Line from port on back of carb. to ????. I thought it must be a pulse line, but not certain, and don't know where to run it to. Please let me know when you find out.
You will have two lines coming from the petcock on the bottom of the gas tank. the small one goes to the front of the number one carb, and the larger one plugs onto the fuel rail in the middle of the 4 carbs on the back. The lines that run between the 1 and 2 carbs and the 3and 4 carbs are just overflow lines, so they don't hook on anywhere else.
one line comes directly from the fuel tank (the one with the filter) to the inlet side of the of the carbruetor ( the bottom fitting on the carb.usually)
the other line coming out of the fuel tank is the return fuel line and it hooks up to the outlet side of the two fittings on the primer bulb
the other side of the primer bulb goes to the only fitting left to hook to at the carbruetor.
you have 2 different length fittings on the primer bulb itself
the longer fitting is your return line hook it up to your tank side and the short one goes to carb.fitting
when you get it hooked up press the bulb several times and see if it primes as it should(fuel moving thru lines) from tank thru carb. thru primer back to tank