1993 Nissan Sunny I smell fumes.

You have to check your evaporative emission system, especially the charcoal canister. Fume is kept in the canister to control fuel smell in the vehicle. Sometimes, when the system solenoid fails, you will smell fuel in the cabin. The first one is for SR2DE, and the latter is for GA16DE. Check every single part for bad /leaky vacuum line and electrical connection.

Unfortunately, if you have crack behind the dash, you will have to remove the dash to patch.

Wait, wait. Fume is the smell of unburned gasoline. Are you smelling the gasoline or the exhaust gas in the cabin?

If you are smelling unburned gasoline, patching your exhaust will not do anything to the problem. You need to check your EVAP system as previously suggested. You may also want to remove your back seat and check the seal on the fuel pump. It may actually leaking from there as well.

That could have been my fault. I am very familiar with US-spec Sentra. I guess Sunny is different when it comes to fuel pump. When you get to your mechanic, tell him to check your evaporative emission system. Look at the vacuum diagram I had provided, and ask him to check the entire system. There is a hole or possibly a blockage in the evap and possibly fuel return systems, not exhaust. Well, you may a hole in the exhaust, but it has little to do with your problem.

Wow. Is that burnt make by the gas cap?

Any way, in the future (for new posting) go under Mitsubishi Proton. And as you write your description, identify Saga 1.3L Magma as your engine. I used to play around with that engine years and years ago. Fume smell can only come from your EVAP system malfunction or leaky fuel system (which I consider part of EVAP system). Here is a typical EVAP system. If you have a leak at any point from the gas cap all the way to the carburator and back to the gas tank via the fuel return hose, you will smell the fume.

The fume you smell close to the filler hose is probably from the black mark close to the gas cap, or possibly a leak in the filler hose going to the gas tank. You still may have a problem with either the charcoal canister or the purge valve (run off vacuum), creating fume in the return line causing the smell to creep up the gas filler hose.

Now the pictures that I posted won't work for you. Those were meant for Nissan Sunny with SR20DE or GA16DE. (That was what I thought you had originally). Regardless, you still have an EVAP system on carburetor-driven fuel system, consisting of very similar parts: charcoal canister, purge valve, solenoid (vacuum operated, rather than computer controlled), return lines, and so forth. I don't have a diagram for Proton Saga unfortunately. Only US-model vehicles.