metal fuel tank imploding??

[83atc200]

ive recently purchased a 1983 atc 200 and i am in the process of fully restoring it.. I have recently restored the fuel tank, pulled dents, professional paint job, internal restoration, new decals, the whole deal.. The fuel cap is the sort with the on/off breather valve on the top, and ive heard horrer stories of tanks having the potential to implode and cause denting if the cap doesnt vent correcly, and i dont want to take the chance after all the time and $ ive put into the tank.. Is this just a wives tale or should i think about purchasing a different sort of fuel cap just to be safe?? any opinions would be much appreciated..

Jake

[Thorpe]

Wives tale... Your motor will die... You will pull and pull, then when it dawns on you the vent is off, you will be thrilled to have been that dumb... (I can only say that because mine has stalled from lack of fuel, and took me 10 minutes to figure out why...)

[83atc200]

sweet, pretty much what i was hoping to hear..thanks/

[Jason125m]

^ happened to me after gassing it up this past weekend.

[MudBug]

Ive seen a tank left half full with gas with the vent turned off, and it sucked in on the sides.

[Flossyb20]

Ive seen a tank left half full with gas with the vent turned off, and it sucked in on the sides.

Likewise..but the dents were easily popped back out with the air compressor.

[Chazz of Blades]

Thats odd, the tank on my 84 big red did the opposite.

At the time I had had it for about two weeks, and the gas vent had been left off, well, the day I'm getting ready to ride I roll it out and into the sun, and have to run in to do something, well that something ended up taking an hour, I went outside and saw the tank was a bit swollen looking, and when I turned the cap of the tank to take the cap off, it popped up about 5 inches into the air, and it pushed a pinhole in on corner of the tank that was previously not leaking a drop. Took forever to get that leak to stop, and it was dripping right down on the exhaust. Just another simple, small mistake that cost alot of time.

[ATCrider42]

I always leave mine on. Don't know if that's the smartest but it's always worked out for me. But i always keep my trikes garaged.

[Thorpe]

Ive seen a tank left half full with gas with the vent turned off, and it sucked in on the sides.

If the system was sealed, and a fuel pump, maybe I could see this. But on a gravity feed fuel system, I call BS...

[Flossyb20]

If the system was sealed, and a fuel pump, maybe I could see this. But on a gravity feed fuel system, I call BS...


When the valve on the cap is turned to off, then the system IS sealed. All it takes is to have a full bowl in the carb, and the least bit a vacuum (temp change) will seal the float needle against the seat...sealing the system completely...I call BS on you!!

[79fordblake]

When the valve on the cap is turned to off, then the system IS sealed. All it takes is to have a full bowl in the carb, and the least bit a vacuum (temp change) will seal the float needle against the seat...sealing the system completely...I call BS on you!!

But if there is enough pressure built up in the tank won't it force its way past the needle and seat in the carb? That is unless you have the vent closed and the fuel shutoff, then pressure can really build in the tank.

[frauke75]

I just bought a 250es that has a tank that is "sucked in" as the seller told me. It was keept at a hunting cabin and one time when he went back it was sucked in. (this was 10years ago)
It is drasticly concave on all 3 sides... and creased. No signs of impact at all.
All I could think was he used it in summer and closed the vent then a northern Wisconsin winter came and.... (I would insert pics if I could figure that out)

I tried to push it out with a bent steal rod but it just started to make little dents so I stopped.
It don't leak so I think I will just leave it.
Thought about compressed air but again do not want it to spring a leak.

[bcredneck]

when i was in high school one of the kids in shop did that after spending weeks making a tank for a mini chopper so he blew air into it and blew the brazing apart

[Red Rider]

I agree, running the bike with the vent closed will cause the bike to stall before it sucks in the sides of the tank. The only way the sides will suck in or bulge out is through fuel contraction or expansion due to atmospheric, temperature, or pressure changes.


...the gas vent had been left off, well, the day I'm getting ready to ride I roll it out and into the sun, and have to run in to do something, well that something ended up taking an hour, I went outside and saw the tank was a bit swollen looking, and when I turned the cap of the tank to take the cap off, it popped up about 5 inches into the air...In Chazz's case, the sun heated the fuel tank, fuel, & air in the tank, causing it to expand, and since the vent was closed the pressure had no where to go, so it blew the tank up like a balloon.


I just bought a 250es that has a tank that is "sucked in" as the seller told me. It was keept at a hunting cabin and one time when he went back it was sucked in. All I could think was he used it in summer and closed the vent then a northern Wisconsin winter came and...Frauke, most likely that's what happened. The vent was closed when it was warmer, then it cooled off, which caused the fuel & air in the tank to contract, which sucked in the sides.

You'll get similar results by transporting your bikes from a high pressure area to a low pressure area, or from a high elevation to a low elevation. I really see no reason to ever close that vent myself.

[bcredneck]

when my carb floats were sticking cloased on my big red i turned off both valves drained the carb shook the trike and turned the gas on it fushed the carb out and fixed it till i got home

[Thorpe]

When the valve on the cap is turned to off, then the system IS sealed. All it takes is to have a full bowl in the carb, and the least bit a vacuum (temp change) will seal the float needle against the seat...sealing the system completely...I call BS on you!!

Sealed yes, sealed well enough to hold against high enough pressure, no. So are you talking about atmosheric pressure changes here, or from the engine running? I can see drastic weather changes, but not from engine vacuum... Are we comparing apples to oranges here?

[rbaral233]

simple fix as they all stated just leave it open. if you ride it enough and its garaged i dont see the issue. i know for myself along with many others you just leave it open and have no issues. it can breathe, you dont need to worry about it, and unless you are transporting it or storing it for winter (which never happens) you should be fine.

[Flossyb20]

Sealed yes, sealed well enough to hold against high enough pressure, no. So are you talking about atmosheric pressure changes here, or from the engine running? I can see drastic weather changes, but not from engine vacuum... Are we comparing apples to oranges here?

I believe everyone here is talking about the weather causing their tanks to suck in - notice we're talking about vacuum here, not high pressure. With both ends sealed, the only left to give is the sides of the tank. Have you seen what 5-10 psi of vacuum will do to a tank? I agree with you in that high pressure should not cause a tank to EXplode in this type of system, as it will be pushed past the bowl, but even with a properly working system, it can still IMplode from negative pressure

[Thorpe]

Well if we are talking weather, I could understand it sucking in the tank. If we are talking engine vacuum, I am not a believer...

[bcredneck]

fill a 2 leter bottle with gas and put it in your freezer watch what happens gas is super sencitive to temp changes

[Red Rider]

I believe everyone here is talking about the weather causing their tanks to suck in - notice we're talking about vacuum here, not high pressure. With both ends sealed, the only left to give is the sides of the tank. Have you seen what 5-10 psi of vacuum will do to a tank? I agree with you in that high pressure should not cause a tank to EXplode in this type of system, as it will be pushed past the bowl, but even with a properly working system, it can still IMplode from negative pressureWell, we are also talking about an ATC 200, which, correct me if I'm wrong, has a gravity fed fuel system. So, once the fuel level drops enough to create a slight vacuum, the fuel will stop flowing, and the engine will die. And there's no way that slight vacuum will be enough to cave in the sides of the metal tank on the ATC 200.

Regardless, all modern bikes have a continuously vented fuel tank (yes, even the metal fuel tanks), so there's no reason to ever close that vent. Problem solved, & case closed.

[Flossyb20]

Well if we are talking weather, I could understand it sucking in the tank. If we are talking engine vacuum, I am not a believer...


Well, we are also talking about an ATC 200, which, correct me if I'm wrong, has a gravity fed fuel system. So, once the fuel level drops enough to create a slight vacuum, the fuel will stop flowing, and the engine will die. And there's no way that slight vacuum will be enough to cave in the sides of the metal tank on the ATC 200.



I agree 100% with both of you here, there's no way that the engine will suck the sides of the tank in, even if the vent is closed. But pressure an temp changes can and will do this..but like rbaral said, just leave the vent open and youdon't have to worry about.

[Bretmd94]

my 200x's have always had a dent on the left side.... I also have a crappy left knee.... I can't figure it out.

[bcredneck]

you guy all seem to forget the fule valve that gose to the carb if thats shut off and the vent is shut off durring the hottest part of the day it should be concaved by night

[Flossyb20]

you guy all seem to forget the fule valve that gose to the carb if thats shut off and the vent is shut off durring the hottest part of the day it should be concaved by night

You're absolutely right!!!

[Red Rider]

you guy all seem to forget the fule valve that gose to the carb if thats shut off and the vent is shut off durring the hottest part of the day it should be concaved by nightAnd the opposite can happen if both valves are shut off during the coldest part of the night. Once it warms up & starts expanding, that pressure has to go somewhere. Will it bulge out the tank in places? Possibly. Can it cause leaks in the tank? Definitely.