So i got my 82 Datsun 720 when i graduated from high school around 2013 it ran great until i had to smog it vac lines are hooked up new plugs Cap, rotar, oil change, my dad put his old carburetor onto it since he was parting it out. When i open the gas tank pressure shoots out everytime and my truck acts as if its starving for gas after about 5 miles. ive seen posts about this stuff except for the gas tank pressure im pretty young and im about tired of it lol, because as we all know the only way to figure a datsuns problem out is to do a full tune up. Ive done that but the pressure is still there and it dosent seenm to be going anywhere. Please let me know you previous experiences if youve came across these problems.

Welcome to NICO! Way to keep it in the family!
I'll try to get you some help with your truck.

In the mean time, check out the link in my signature. It has a Factory Service Manual for most years and models. You may be able to find some potential solutions in there!

Not sure if those had carbon canisters or not, but that's usually the first place to look.
Does it run normally if you drive around with the cap loose?

Welcome aboard Tae!

Let's start right here. This looks like a lot of work, but I'm almost positive you'll find the issue lies in this area:

http://www.nicoclub.com/archives/nissan ... guide.html

Carbon Canister, ill look into that. Thank you guys for the response i will also look into that service manual. Now that i think about it the Carbon canister could be the reason ill check it out in the morning.

My '84 was pressuring up in the tank, but in a different, weird situation. My truck is the chassis for an RV, and somewhere along the line a previous owner installed an oversized 23 gal aftermarket tank. Turns out the vapor takeup tube in the tank must stick a little ways down into the tank from the top, but the fill tube is higher, on the side of the tank. I discovered that if I absolutely fill the fuel tank to the top at the gas station with cold gasoline, I'd better drive a good 100 miles right away. As the day warms up the gas in the tank, it expands, and if it was already within a couple of gallons of completely full, the liquid gas starts pushing up the vapor line under pressure to the canister. It then dumps out the bottom of the canister and goes.. wherever, under the hood, and not a small amount! Man, scary when that happened.

There's a filter on the bottom of the canister, possibly plugged up? I think you can order 'em from RockAuto, they're not expensive. Heh, the canister itself oughta not go bad, but it's $150 for a new one!

I'd first check the rubber tube from the fuel tank to the canister. The canister runs under engine vacuum, and my understanding is the canister vacuum is used to pull raw gas vapor into this emissions control system from the tank. If that's true, the tank should not pressurize. My tank, though subject to the overpressure above when completely full, actually has negative pressure and sucks in air when I open the gas cap up on empty at the gas station, it's under a bit of a vacuum when I first shut the engine off. So, if you're seeing positive pressure at the gas cap, I'd check to see if the line from the tank to the canister is plugged up.

Good luck!