Pressure in the gas tank

[Jeff Berk]

Kully, The carbon can was removed by a PO and the car seemed to run correctly except for a vapor lock issue. Unfortunately, a PO also deleted the fuel return and made this a dead head system. That likely contributed to vapor lock  under certain conditions (e.g. between autocross runs). I recently reestablished a return fuel flow by connecting to the abandoned return line. My car had a fuel pressure regulator installed before the carburetors but it seemed more straight forward to have the regulator after the carb's if I was adding the return line back in. 

It appears that my vapor line to the canister is plugged as I cannot suck air out of either end and cannot blow air into the canister end.

I am going to cut the vapor line at the right rear fender to allow the vapor to escape. Hopefully that will take care of the pressure buildup in the tank and fuel line. 

[kully 560]

I do not know why I can't blow back to the vapor tank also from where the canister is at all on my 260z. [hot or cold] but I can only suck air when after the car was just driven. I did check for pressure at the gas cap, and I do not have any at all. I know you are not running the canister, but you think the line is plugged? I guess what I am saying is mine seems to not flow back from the canister at all anytime. but when the car is hot it will flow air from the vapor tank to the canister. [only when hot] now in the fsm it only shows an orifice in the line from vapor tank to canister not a 1-way valve. did you happen to try on the gas filler neck just below the gas cap and blow air back to the vapor tank? I am also trying to understand this flow thing that I have as compared to yours. it seems that mine is working correctly and only flows when needed. I never looked into the top of the vapor tank to see if there is a build in check valve for a 1- way vapor flow. I am looking forward to the results from when you cut the line. that should tell all.

[Jeff Berk]

Kully... I ended up cutting my vapor line at the right rear fender. While at it tried pulling a suction on the line. The line to the top of the reservoir tank drew air when a suction was applied. When applied to the line from the right rear wheel to the engine compartment, it held a vacuum.  There was some water accumulated in the line I cut which was a low point.

The car seems to be running fine at this time and the pressure issue (and I think the fuel overflow at the carb) seem to be resolved. 

I don't think the reservoir tank has a valve at the top but I cannot tell for sure since I cant open the top.  The connection on the gas filler neck I think just drains into the reservoir. 

[kully 560]

yes, the connection at the top of the filler neck does drain into the reservoir tank! I was hoping it was not clogged for you. maybe the line is plugged from the water-rust. but like I was saying I can't draw vacuum from front to back until the car is hot, that I can't understand. I am glad that it looks like your problem is solved!!