Vented Gas Cap???
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Road Captain
Joined: Jul 2014
Posts: 721
Likes: 18
From: Galesville, WI
Vented Gas Cap???
I am just curious if my gas cap is of the vented type? 1991 FLHTC - EG Classic EVO. When I go to fill up the tank releases pressure. Is this normal on these older tanks?
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Road Captain
Joined: Jul 2014
Posts: 721
Likes: 18
From: Galesville, WI
110 views and no replies? Come on guys, should be a fairly simple answer. Help me out please, Thanks!
EDIT: Service Manual says that FLH model years 1984-1991 fuel tanks are vented thru the fuel cap. So I can only assume then that since I am hearing pressure release when removing the cap to fuel up that the vent is probably plugged? So this in turn would restrict my fuel pressure to the carb? As I also assume I have a gravity fed carburetor?
Thoughts? Suggestions?
EDIT: Service Manual says that FLH model years 1984-1991 fuel tanks are vented thru the fuel cap. So I can only assume then that since I am hearing pressure release when removing the cap to fuel up that the vent is probably plugged? So this in turn would restrict my fuel pressure to the carb? As I also assume I have a gravity fed carburetor?
Thoughts? Suggestions?
Last edited by DeputyLoud; Sep 29, 2014 at 03:48 PM.
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Road Captain
Joined: Jul 2014
Posts: 721
Likes: 18
From: Galesville, WI
Recently I had an issue with my accellerator pump spray not being consistent and bike would run real rough at times. Seems to be worse in colder weather. It's been good for a couple weeks, but the other night it happened again for a short while. I do plan on installing a full rebuild kit in the S&S SuperE carb this winter. I was just wondering if my tank isn't venting properly restricting fuel flow to my carb at times. The fact that it always seems to happen when the weather is cold. This must have some effect on the expansion of the fuel, tank, lines, gaskets etc...
I just read thru this thread and in the end the guy said his tank quit releasing the pressure when removing the cap by simply flipping the cap gasket seal around. But then there was no more posts. That was back in 2012. So was it a solution? Who knows.
https://www.hdforums.com/forum/evo-c...ed-or-not.html
So I don't know if I have an issue or not really. My tank does have the vent line from the console and the filler neck. But I also assume some vaccum and pressure is normal. But should I always hear the pressure release when removing the cap?
I just read thru this thread and in the end the guy said his tank quit releasing the pressure when removing the cap by simply flipping the cap gasket seal around. But then there was no more posts. That was back in 2012. So was it a solution? Who knows.
https://www.hdforums.com/forum/evo-c...ed-or-not.html
So I don't know if I have an issue or not really. My tank does have the vent line from the console and the filler neck. But I also assume some vaccum and pressure is normal. But should I always hear the pressure release when removing the cap?
Cruiser
Joined: Aug 2014
Posts: 185
Likes: 0
From: Adamsville, Al.
My guess is that your actually hearing air sucked into the tank as you back the cap off, if your vented cap isn't venting. I've seen this happen on a softail style tank. It would suck one side of the tank dry, but because the vented cap on the other side wasn't venting, the fuel from the other side of the tank wouldn't cross over and you'd run out of gas to the carb. Pull off the road and open the cap and there's plenty of gas showing. Hearing that sucking sound while taking the cap off is how I found the problem. New cap fixed that one.
Dirt don't hurt
Joined: Jan 2011
Posts: 21,065
Likes: 4,561
From: Haslet Texas
From personal experience on a Softail with a plugged vent line the motor cuts out really bad till the vacuum is gone.
It takes less than a mile for the vacuum to start causing problems.
It takes less than a mile for the vacuum to start causing problems.
Seasoned HDF Member
Joined: Aug 2007
Posts: 8,199
Likes: 3,087
From: NW AR
I've heard a "woosh" sound when removing the cap off and on for 28 years. I have heard of people with gas cap problems, but not on FLHT's. I would suspect your carb first. You are probably too lean and when it is cold out, that is putting you over the edge of "close enough" that a carb does. You can test this by waiting until the next time it is acting up and then partially undoing your gas cap. If it is all OK after that, your gas cap is the problem.
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Road Master
Joined: Oct 2011
Posts: 957
Likes: 2
From: Carlsbad Springs Ontario
check your manual .
I've heard a "woosh" sound when removing the cap off and on for 28 years. I have heard of people with gas cap problems, but not on FLHT's. I would suspect your carb first. You are probably too lean and when it is cold out, that is putting you over the edge of "close enough" that a carb does. You can test this by waiting until the next time it is acting up and then partially undoing your gas cap. If it is all OK after that, your gas cap is the problem.
Do as Dr. Hess describes and run with a loose cap to evaluate .
Gas tank breathing troubles usually indicate a bad cap.
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Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,898
From: Bedford UK
On my 1990 tank there is a breather pipe on the filler neck that was blocked as it came out of the factory. Remove the chrome dash to see it. I don't recall why now, but I drilled it out on mine.
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Road Captain
Joined: Jul 2014
Posts: 721
Likes: 18
From: Galesville, WI
Here's a pic of a page right out of my service manual. The paragraph on the right explains the procedure for drilling out the vent tube on a new california model tank. I do believe I have a vent tube coming from the filler neck, and there is also one attached to the console. I don't think I have a california model. Do all of these have a vent tube anyways? Is this where the cap will vent to even if I don't have all the california vent valve and canister crap? If and when the cap vents open I can imagine the vented air being pushed out through this tube. Is this correct?
Last edited by DeputyLoud; Sep 30, 2014 at 07:39 AM.