Welcome. Thank you for choosing Just Answer.
what "rebuild diagrams" are you looking at?
that PDF is parts pages for SNOWMOBILES and has nothing to do with a 1974 Harley Ironhead 1000.
this is NOT your carb.
here is a link to a blow up of your carb http://www.dansmc.com/carbs/HD_Carbs/HD_Bendix_16P12.htm
your bike has 1 fuel line and NO return line.
the fuel line attach's to the fuel petcock on the fuel tank. the other end attach's to the fuel inlet on the carb.
the stock carb for your bike is on the lower left side of the page on this link http://customchromecatalog.com/2011/full.asp?page=583
the fuel inlet is on the left side.
your carb has a float bowl over flow outlet to prevent flooding the engine with raw fuel should the float/float needle fail to shut off the fuel.
you should remove the float bowl and clean/inspect the fuel inlet seat, float needle and float.
the rubber tip on the needle should be soft and rubbery. if it has hardened, the needle will need to be replaced.
if the float has cracked or developed a hole and has fuel inside it, it will need to be replaced.
ensure the fuel inlet seat is clean and there is not debris in the float bowl to prevent the needle from seating in the inlet.
let me know if you need more help.
I am having some trouble following your description, however, the brass tube sticking up in the throat of the carb is the main jet holder.
if fuel is squirting up through there, you have a float/fuel inlet problem.
read my answer above and find and correct the issue.
remove the fuel filter. throw it in the trash.
if you have junk in the fuel tank....clean the fuel tank.
purchase a HD factory service manual.
the one I have has no part number, so I'll do a little digging and see if I can find you one.
sorry for the delay.
check out this link http://www.diyrepairmanuals.com/products.asp?cat=14257
I highly recommend the purchase of BOTH, the Service manual AND the parts catalog.
by original factory HD manuals only.
Clymer and Haynes are not recommended. they contain mis-information.