Jump to content

- - - - -

Pressure Building in Gas Tank (510)

  • Please log in to reply
25 replies to this topic

#21 datzenmike



  • User Administrator
  • 72,245 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 31 October 2017 - 04:26 PM

Usually marked vent, vacuum and purge.


Vent to the gas tank and on newer 720s also to the carb vent to collect boiled off gas after shutdown.

Vacuum. Anywhere on the intake to suck fumes stored in the charcoal.

Purge is just a vacuum signal to say the engine is running  and allows intake vacuum to empty the canister. Usually from the ported vacuum advance so it only operates above idle and when the engine has warmed up.

Posted Image

#22 BambooU



  • Members
  • PipPip
  • 69 posts
  • Location:Bay Area/Los Altos, California
  • Cars:1969 2-door 510

Posted 01 November 2017 - 01:04 PM

I found a generic charcoal canister a couple months ago, but I can't remember who made it. Any old canister will work, but the smaller, older ones look better in a vintage car. Something from a 1980's Toyota maybe.. They are metal and have steel connections so they look good and won't break, plus, they are pretty compact.


I have a canister lying around somewhere, i just need to find it. Still haven't noticed gas smell, despite having several holes in my firewall :3

#23 datzenmike



  • User Administrator
  • 72,245 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 01 November 2017 - 06:55 PM

You may not smell anything but it is a 'loose end' and should be addressed. Vent open to gas tank inside the engine compartment where there are ignition sparks. The charcoal canister is totally benign in operation.

Posted Image

#24 distributorguy


    Senior Member

  • Senior Member
  • PipPipPipPip
  • 1,208 posts
  • Location:Metropolis, MN
  • Cars:77 Datsun 620, 73 Datsun 620

Posted 02 November 2017 - 08:57 AM

You will be sucking air into the line so you won't smell fumes until its parked for a while.  Venting through charcoal will eventually smell like fuel as well.  You can run a vent hose high in the engine bay and install a fuel filter on the end of it to reduce potential contamination.  Tanksinc.com sells a fitting that also acts as an anti-rollover valve so if you tip the car fuel won't spill out.  

#25 Stoffregen Motorsports

Stoffregen Motorsports

    Datsun Mechanic

  • Senior Member
  • PipPipPipPipPip
  • 4,184 posts
  • Location:Cool, CA
  • Cars:http://www.4wdandsportutility.com/features/rover/0611_4wd_1957_range_rover/viewall.html

Posted 03 November 2017 - 08:22 AM

I made the mistake of venting the fuel tank in my Land Rover (rock crawler) to the valve cover PCV breather hose (with a tee). Thinking it would help act as a sort of roll over protection. Now, when I'm on a steep downhill, it sucks fuel (or maybe vapor) into the system and chokes it out.


So you should be careful where you vent the tank to. If you vent it into the engine bay, think about getting it as far away from the exhaust as you can. Unless you run a charcoal canister, then it doesn't really matter.


Old Chevy trucks have a hose that runs all the way up to the radiator support and the hose is capped with a breather.

#26 hang_510


    too ol'skool

  • Senior Member
  • PipPipPipPipPip
  • 9,696 posts
  • Location:so.cal
  • Cars:71 2 door - LZ22 / 72 wagon - TBD

Posted 03 November 2017 - 09:18 AM

I had a similar thing happen
I got out and the tank had imploded. Looked like a squashed banana

I had so much vacuum on a 4dr, it collapsed the tank.
I was able to use bar soap on the cracks to make it home.
Clogged vent line was the cause.

I forgot I put 2 filters on mine.
Spent 2 days figuring out why the fuel pressure was below 1 psi and so much vacuum.
2 new filters and it screams again.

"I can spend time working on the Dattos, or wasting money at the strip club. You make the call." :D

I'll put on chain mail and a dirt bike tire jock strap and drive it!!!!!