I gotta get me one of these.
Get yourself a Mityvac.
The plastic ones are OK provided you never let fuel get in them.
I started off with a brake bleeder for vacuum & a bulb pump for pressure.
And wile they did work, using the one tool is so much easier & quicker
On the first test Donny did ( he is one of the better presenters ) you would test both for pressure tightness ( I go to 10 psi ) then switch over to vacuum
The inlet line should hold 10psi ( 7 is also fine ) and also hold a vacuum
You then leave the tester in place and pull a vacuum with the primer / purge bulb before disconnecting & going to the return line,
Where you do as shown plus check that it will not hold a vacuum.
You can do all of that with the cab in place.
If it passes all of those tests then the only other thing that could be wrong is a blocked jet or stuck check valve.
With the carb still in place you hook up to the return line and pressurise the tank.
It should hold 10 psi, minimum and not hold a vacuum.
If it does not hold pressure then you check the grommets & cap for leaks.
I like to uncap the supply line and give the tank a single stroke of pressure to see if the fuel flows continually till the tank pressure drops off to 0 ( shows the filter is good ).
Obviously you have not found the Joe pace videos I mentioned previously. Do it now.
Then if you are still unsure there is a painfully boring Pom who presents his 2 stroke classes as if he was teaching intellectually challenged people.
painful to watch ( and there about 20 of them ) but worth doing if you are going to be doing this for business.