Whats up with these gas tank caps?

ran49

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Mar 5, 2008
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Well they do keep the mice out.Aside from that not much better than a rag stuffed in there.I realize the tank needs venting but I think I might get another 10 miles a gallon if I wasn't sloshing it all about.I thought about stuffing the hollow can that extends down from the lid with air filter element but that would just create a mess when you removed it.
Starting to look like a good excuse to make a custom tank.Any good source for a tank cap and threaded fitting?Thanks,Ron
 

paul

Well-Known Member
Dec 23, 2007
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i got a gallon tank from motorbike mike. i dont fill it all the way so not having gas come out. if i could be more careful filling it i would be all set lol
 

ran49

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Mar 5, 2008
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Checking around for gas tank fittings I found out that along with a cap you would need a "female boss" well a man shouldn't have to search too far to find one of those!LOL,Ron
 
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Ilikeabikea

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Jan 27, 2008
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I asked the "female boss" about posting a picture in the swap shop. Oh well I enjoy sleeping on the couch in the den..........................:-||
 

deacon

minor bike philosopher
Jan 15, 2008
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I wonder if you couldn't just take the cap we have to the auto parts store and try matching it up with one that isn't vented. I have had lawn mower with those off set vent holes Joe mentioned. Gas didn't slosh but it always smelled of gas when the weather changed.
 

Ilikeabikea

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I just always leave mine about an inch or so below the neck and don't have any trouble with sloshing........................
 

RedB66

Active Member
Dec 28, 2007
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Sunshine State
After several ruined paint jobs and the discovery of gas resistant clear coating I fixed my problem by adding another gasket. I made it from a heavy duty inner tube. I tried placing it behind the original to take up some space and get a better seal but discovered that it worked best by placing the additional gasket on top of the existing one. I haven't had any problems with venting.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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What I did was to drill a very small hole with my pin vise drill on the top side of the cap (cant see it). Then I drilled another in the middle underside of the cap.

I think what happens is that the gas sloshes and also gets warmer and then when it splashes up on the cap gasket, the pressure tends to force it out. When I vented my tanks, I never had a problem again.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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I drilled a hole in the top center of both my caps. What was happening on my bike was the fuel would slosh and the engine would warm it and it would pressurize the tank a little, then when the fuel splashed up near the filler neck, it was forced out around the crappy gasket.

I haven't had any problems since I drilled them.
 

deacon

minor bike philosopher
Jan 15, 2008
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Great idea, I think I'll make one and put it on today. I don't have a problem because my tank is at a funky angle. But one never knows what will happen on any given day.

Gas is really known to expand in the tank. They used to say fill your car first thing in the morning and you get more gas because it is more dense. It will expand as the day goes on. So I wouldn't fill mine when its cool then store it. Fill it then ride it I think would be best.

That is true about the expansion I have filled my car then driven home a few blocks left it all day and found a puddle at noon.
 
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ran49

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Mar 5, 2008
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Just to be sure is this the same cap you guys are talking about.Notice vent hole inside rim(very bottom of pic).It seems to allow gas to pass through and around any seal you might have with "boss".Ron
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SeattleMike

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Mar 17, 2008
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Seattle, WA
Maybe I'm lucky, but my cap and tank have been great. I fill mine up, no sloshing. Today I had to take the tank off to install a new exhaust pipe, and I even dropped it when it was full of gas, it didn't hit the floor because the fuel like was still connected so when I dropped it, it dangled from the carburetor. I freaked out, when I realized I dropped it and it yanked by the fuel line, I totally expected gas to leak out all over me, the bike, and the soft wooden floors of my shed, but not a single drop came out! It was amazing. It seems to vent fine too, but the weather has been cold since I've gotten it. Also, I always use a funnel when I put gas in the tank, to make sure I don't get a drop on the tank when I fill it up.