Fuel caps---to vent or not to vent---

[51Hog]

My stock 51 FL has the stock setup for fuel lines on the tanks---Cross over from right to left, and feed to the carb from left tank. When I got the bike, both gas caps were vented, bike ran great, and used all of the fuel in the tanks. If I filled her up, and put her on the side stand, fuel would run out of the left gas cap. Cap seals are good.
I bought a non vented cap, put it on the left tank, and no more leaks at the left tank when full.
Problem is this: Bike runs great until tanks start to run low, but before reserve is needed. Then the Motor will shut down until I open the non vented tank cap.
Shurley I am missing something.

[fourthgear]

51hog
See if you have a top tank to tank vent line under the dash .Make sure the top , cross over line is not pluged or restricted or crushed . The left tank vents from right tank , if there is a restriction , it will not let gas gravity feed .

[51Hog]

When I assembled the bike after repainting, there were only two lines----The crossover from right to left, and the left tank to carb. There were no other fittings on the tanks.
Thanks

[fourthgear]

51hog
I am not that experanced with the thru tank valve system and you may very well need to have vented caps on both tanks. Someone here has had the same problem , you may have to shut the valve off so you don't get equilization of the tanks when on stand. This may be why later tanks have a top tank to tank vent. I can't remember how my 56 was set up , too long ago . Some one here will jump in and let us know . good luck .

[51Hog]

Clymers says that 48-64 had both caps vented.
65 Electra had the right cap vented and the left cap not vented.
Can anyone verify that this is correct? I can't find this info in Palmers book.

[mbskeam]

hello,
Went out and looked at a set of oem HD tanks , 53 I think,
it does not have a top cross over tube. my repop tanks do have a tube.
mbskeam

[03Roadking]

I am curious about this my self I have older fat bob tanks they have the vent tube under the dash and the equalizing tube at the front lower with the shut off on the left The fill cap is on the left it appears to be vented but the cap on the right will not budge I have gotten on it with both hands and it will not twist off I would like to change sides so the fill would be on the right because I can only put in 3 gallons at a time if I put in more and don't ride till the level goes down it leaks out while it is on the kick stand I want to put a wrench to the right cap but I am afraid I would tear up the fitting I don't care about the cap. but can you swap sides on these???

[PanPal]

03

You may want to try a strap wrench to get a little extra leverage. You may have Eaton caps and wouldn't want to damage originals. If you have the upper vent tube, you can use an unvented cap on your left tank.

[Cotten]

When cold gas out of the pump expands from sunlight or motor heat, it gets messy no matter what caps you run.
(Again, Rats Rule.)

Beware also of repop caps with the vents located under the rubber seal. The seal swells in modern fuels, and blocks the vents! If the right cap will not vent, then the left cap will purge no matter what. There goes your paint.

(I lost ~ $750 learning that one. )

All of my '65s have/had 3.5g Police tanks, so I can only trust to a feeble memory that the 5 gallon tanks still had the old short bayonet bungs. Even 66's changed things mid year.

[King]

Hi 51 Hog

My 51 FL is set-up exactly as you describe and does the same act when the fuel gets down to about an an inch or so above the reserve. I think that is the nature of the beast and as you noted, Clymers does say that both caps should be vented. When I use a non-vented cap on the left other wierd things also happen such as all the fuel moving to the left tank and when I shut her down fuel gurgles from left to right for about a half hour. This is totally against the laws of physics and the rule of reason, I know, but we are dealing with Panheads here.

Of course having a vented cap on the left causes fuel to leak out while on the jiffy stand which is especially scarry when starting. I have gotten around the problem by using a non-vented cap on the left when I fill her up and carrying a vented cap in my pocket which I swap for the non-vented one when under way. And I mean vented. I took one of the old tractor tank caps with the upright twisters and drilled two holes through it to be damn sure. I know it's not elegant but it works.

Good luck and good rides.

King

[PanPal]

A guy recently told me I should rest the kick stand on a small piece of 2 x 4 for two reasons. One it keeps oil from coming out of your tranny and two to keep the left tank from leaking on your paint. I have kids playing close to my bike constantly, so I don't want to take the chance of having them tip it from this more upright position. But it makes sense.

[03Roadking]

I am gong to try a couple of ideas to see what I can come up with I'm sure some of you have pondered this longer but it's worth a shot
PanPal I had the same idea about the block of wood but before I tried it Divine intervention intervened I live in Calif. and two Sundays ago I was in the garage putting my tools in my roll-away when there was this loud thud on the roof and then the hole place went left to right for about 20 seconds I watched the Pan and my roadking rock up almost upright and then fall back down on there jiffy stands Earthquakes it's always nice to have mother nature stop by

[RussW]

Aftermarket caps can be very poorly made. I run a vented cap on both sides of my stock 1961 tanks. A set I have found that does not seem leak-prone, but vent well, are available from Tucker-Rocky (Bikers Choice). They are called " Late Gas Caps, Stainless Steel Vented. Mfg. # ACO-3917, Ref. # 61102-/3". They are a one-way valve deal, where you can suck air into the vent hole in the center, but you can't blow air(or gas) out. I've been using them a few years now, and no gas leaking out of the left tank when parked.

[sleeper]

03-
My brother in-law lives near Modesto & when he parks his '53 Pan in shop he has made a strap to quickly put around his handlebar.
I guess he has had 'mother nature' visits as well..
Only now his bikes don't fall over..