Vacuum in fuel tank (sierra)

Post by **nicbeer** » Mon Sep 19, 2005 1:18 pm

Hey,

Wondering what would be causing this and how to fix it.

The fuel tank is getting enough vacuum when running to crush the filler neck hose. Very hard to take the cap off the tank also with this vacuum in there. I have changed the cap with a mates one and still did the same problem.

is this carbon canister prob or venting somewhere?

thanks

Nic

Post by **Pat Murray** » Mon Sep 19, 2005 1:33 pm

I doubt it mate. My Zook has no pollution gear at all but I still get a vacuum situation myself. Only when the tank is very low and never enough to cause a motor problem.

Post by **nicbeer** » Mon Sep 19, 2005 2:01 pm

Tank was full and also when 1/2full has same problem. I know a small bit is usual bit this is a bit much to the point i have to use a screwdriver to open the cap sometimes.

Actually crushes the filler tube. I think this may be causing some of my carby problems.

cheers

Post by **-Mick-** » Mon Sep 19, 2005 2:04 pm

add a breather somewhere nic if there isn't one

Just find somewhere suitable

Post by **nicbeer** » Mon Sep 19, 2005 2:17 pm

-Mick- wrote:add a breather somewhere nic if there isn't one Just find somewhere suitable

Thats what i was thinking, i know these breath somewhere, anyone know where from and to - thinking mine might be clogged with mud or something.

cheers

Post by **muppet_man67** » Mon Sep 19, 2005 2:34 pm

they breath through the carbon canister. its probably blocked try disconecting it and see if the problem continues.

Post by **christover1** » Mon Sep 19, 2005 2:40 pm

earlier sierras had no breather line, and used a vented cap.
later vent thru the carbon cannister and have a sealed cap. check your tank for number of fuel lines. parts get mixed up over time.
theres the main line to the carb and a smaller return, and another for the carbon cannister (via a bottle thing near the filler)
they can block the other way, too, and not let pressure out when parked in sun (mine spewed fuel out thru the carb when parked)
I reckon a vented cap may fix it.
I've had 3 cannisters die on me, so I ran a breather pipe of my own with a filter on the end.(I will get a better/proper cannister again)

christover

Post by **nicbeer** » Mon Sep 19, 2005 2:54 pm

christover1 wrote:earlier sierras had no breather line, and used a vented cap.
later vent thru the carbon cannister and have a sealed cap. check your tank for number of fuel lines. parts get mixed up over time.
theres the main line to the carb and a smaller return, and another for the carbon cannister (via a bottle thing near the filler)
they can block the other way, too, and not let pressure out when parked in sun (mine spewed fuel out thru the carb when parked)
I reckon a vented cap may fix it.
I've had 3 cannisters die on me, so I ran a breather pipe of my own with a filter on the end.(I will get a better/proper cannister again)

christover

Thanks chris. I will check the canister out and the bottle at the back thingo. i think mine is starving it so no fuel can be picked up sometimes.

Any idea on how many lines means it needs a vented cap or not?, i think mine has 3 lines but will have to look again.

cheers

Post by **christover1** » Mon Sep 19, 2005 3:33 pm

most are 3 lines with a carbon cannister.
some may be 3 lines, but just an open vent line (probly not stock)
very few are 2 lines without a cannister, and using a vented cap.
the previous owner of mine just drilled a hole through the key hole on the cap

to solve his prob. (I only knew after my 1st near roll, as a little fountain of fuel came out)
My money is on the cannister, or a squashed /blocked line somewhere.

christover

Post by **TUFF MAV** » Mon Sep 19, 2005 9:42 pm

Make sure the vacuum hose has vacuum at the canister when you rev it.

Kyle

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Vacuum in fuel tank (sierra)

Vacuum in fuel tank (sierra)

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