When I try to fill the tank on my '79 RX7, it develops back pressure at the fill spout. It can only be filled about 5/8th's of the way. I am assuming this implies that the vent is somehow plugged. Is it on the top of the tank and if so, does the tank have to be dropped to either clean it or replace it?
I did follow advice on the sender unit for the fuel and after cleaning the connectors, it seems to be working great! ( So, thank You) I appreciate the advice. .

 

First I would just hold the filler for the gas out a bit so it lets fumes not be captured by the gas fill nozzle to get a full tank. If you still have the full vent system and the charcoal canister up front, it may just be a clogged canister or faulty valve for it. I would unplug the vent line as it comes up to the engine bay and try filling it.

 

Earlier this year, while we were still poking at the sender unit issue, I had occasion to simply unscrew the gas cap. Compressed fumes from the tank blew right back at me in no small amount. What I am wondering is exactly where the relief vale is located? Am I going to have to drop the tank to get at it? I will look for a line heading to the engine.

 

There is a fuel vapor valve at the tank (never heard of it causing a problem), a ventilation and check valve at the rear of the rats nest and then on a series 1 (SA 79-80) there is a charcoal canister built into the top of the air cleaner. Page 97 of the 1980 FSM describes these and how to test them. I would try disconnect the hose going into the side of the ventilation and check valve and see if its causing a blockage. You can trace the hose as its attached to the hardline coming from the tank for the ventilation.

 

thank you. I had noted the charcoal filter on the air cleaner but had not figured out why it would be there or what it was supposed to do. . I assume by the "rats nest", you mean that tangle of stuff on top of "the dog and pony" show ( another technical term) The air filter area does look like it takes a beating given its paint condition. Anyone selling that top, in excellent condition, I'd likely buy it. It looks like a major PIA to repaint.

 

The vent line that Tim is referring to, coming from the tank and connecting to the ventilation and check valve.




From the Haynes manual: