The Monojets came with lots of combinations of hose ports. I've got one that has 4 ports. 3 are small ones (about 4 mm across) and one is large (about 10 mm). If your carb has a different number, then the ones I can describe are going to have the same purpose.
The one at the bottom front next to the mixture screw is a manifold vacuum. It's usually capped off on trucks, and is most often connected to the carbon canister system on cars. If you have any other small ports on the base of the carb (the same height as the mixture screw), they are also manifold vacuum.
The one on the passenger side under the electric choke is a ported vacuum. It normally is connected to the distributor vacuum advance regardless of vehicle.
There is a small one up high on the drivers side, and is a manifold vacuum. When it is used, it is usually routed to the air cleaner cold-air door or to a solenoid mounted on the firewall on some cars (taxis) and larger trucks.
The large one, which is also up high on the drivers side, is a vent that is connected to the carbon canister (if equipped) or capped off if there isn't a canister system.
Manifold vacuum is normally used to operate on-off devices. Ported vacuum is normally used for distributor advance and EGR valves. There are exceptions to this, and you have to know what type of device you are dealing with to get it correct. For example, some cars used a water-heated switch to send either manifold or ported vacuum to the distributor. You can get by with hooking the distributor to only ported vacuum. You should also test the vacuum advance pot to see if it holds vacuum. Hook a (clean!) hose to it and suck on it when the engine is running. The motor should speed up a lot. If it doesn't, there is a problem, and it easily could affect your gas mileage.
Up here in the States, all cars had a sticker under the hood when they were new that showed how the hoses were to be connected. Does your car have a sticker on it, or did it ever come with one? I've seen more than a couple cars that were manufactured in Mexico that did not have any sticker, and used technology that was at least 10 years behind what the US manufacturers were selling at the time.
Keep on trying, and get back with your testing results
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David
newbie #4153
