74 B210 1.3 cleaned tank and lines, Idles smooth but hisses loudly from gas cap. Any Ideas why? Also, the above is all orig with an auto, but I have a low mile 1.4 & 5spd, do the swap or keep orig. What do you all think?

try finding and unblocking the breather lines that go from the fueltank to the atmosphere (usually in the wheelarches) remember the engine is taking fuel from the tank and if that volume cant be filled with air because none can enter the tank than you are creating pressure in the tank.

Have you checked the seal on the cap. If it's hot and the seal is perished it may hiss.
Quote:

A13 B210s have a sealed fuel system. There should be no vent line to atmosphere. Instead it vents in the engine compartment to the charcoal cannister.

Perhaps the fuel check valve is bad. This is an inline valve near the fuel tank, in the vapor vent line. It is a one-way valve. You should be able to blow air through (with your mouth) from fuel tank side, but not blow through from engine side. Perhaps it is stuck. Details and test procedure are here: club wiki - Gas Cap

The gas tank cap should be sealed type. It does not let air out. But it does have a vacuum release valve to let air in. Perhaps it has the wrong cap. It should be more or less flat on the outside, with a nubbin on the inside. You should not be able to blow air out throw the cap, but should be able to suck air in through the nubbin.

Maybe the problem is in how the lines are connected in the engine compartment. On the round black charcoal cannister are three lines:
* Hose to carburetor side (vacuum signal line)
* Hose to carburetor side (purge line)
* Hose to fuel tank (vapor vent line)
Ensure they are connected.

if you dont run a canister
how else can you stop the pressure build up???

i have same problem when i go to put petroll in a gush of air comes out
lots of pressure aspecialy when hot day

Japan-market 1200s used a simple vented line, just vents to the atmosphere.

What does an Australian 1200 have?



Fuel Tank Venting