fuel tank mystery?

4 replies to this topic
  • Dean400

Posted February 24, 2004 - 09:28 PM


I've been wondering why the fuel petcock on my tank is not the lowest part of the tank. The bottom right of the tank has this ear that reaches way down below the petcock. Doesn't this mean the bike could run out of fuel even though there is still fuel in the tank? My aftermarket tank is the same way. Does anyone know why this is?

  • iron_savior

Posted February 24, 2004 - 11:04 PM


i was thinking the exact same thing

i have a clarke 4.3 gal tank, and the left side is way lower
than the right side, and i would also like to know how does
the fuel actually get to other side where the petcock is ?


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  • BlueRules

Posted February 25, 2004 - 02:23 AM


I suppose if you're really low on juice u can tip the bike on its side to get the fuel over and get another mile or 2!

  • gomopar440

Posted February 25, 2004 - 03:43 AM


Just make sure you do a couple of wheelies now and then, it'll get to the petcock :).

Seriously though, the petcock location could be lack of enginering on their part, but more likely it's a matter of gravity. If you look at the petcock in relation to the carb it is probably close to the same height as the float bowl or higher. If the petcock was lower then the fuel would have to travel uphill to the carb. So the petcock can really only go so low before it will not work properly (usually when the fuel level itself gets below the float bowl).

Also it's about numbers. If your'e shopping for a larger tank MFG's know you look at the total capacity, not useable capacity (I don't know of any MFG that gives that number). So after you get the biggest mofo out there and bring it home do you notice details like this. If it really bothers you, there is a way to keep the petcock drawing the fuel all the way from the bottom. Radio Control airplanes and helicopters use small plastic tanks that have a rubber stopper with brass tubes through it for fuel flow and venting. This acts like a petcock with no valve. Inside the tank a piece of silicone hose, long enough to reach the bottom of the tank, is safety wired to the draw tube and a hollow brass weight attached to the other side. The weight usually stays at the lowest point of the tank (normally where the fuel is also). This is the best way I know of to get the most out of a tank, but you still have to keep the gravity feed issue in mind. Unless you were to also pressurize the tank like a R/C airplane or add a fuel pump, the fuel flow would be questionable once it got below the float bowl level. Another thing to keep in mind if you try this is that the flexible silicon hose is designed to move around as the plane rolls pitches and flips (hey, maybe Pastrana could use this idea :D) in order to follow where the fuel goes. This may cause stress on the petcock at the place where you would tie the hose and keep that weight banging around the inside of the tank.

Personaly, I'd just go until I run out then switch to reserve. If I can't find fuel by the time that runs out then I lay the bike on the petcock side and keep on (prayin for gas the whole way :D)

Ps: The wheelie trick really does work too :D :D :D

  • Frostbite

Posted February 25, 2004 - 04:33 AM


I just put a 4 gallon jug on my 99 400. I read the posts where people are worried about fuel being trapped in the lower part of the tank and some tanks have 2 petcocks and then there's problems routing lines and .......The right side saddlebag of my 4 gallon tank is thicker than the stocker but no lower. Both are quite a bit lower than the petcock so you'd think that the gas could get trapped. I also hear lots about laying the bike over to get the gas to the petcock side. I run out of gas once in awhile and the tank is pretty much empty, even the saddlebag. My guess is that when you accelerate, fuel moves to the back of the tank and when you back off it flows back, half to the petcock side and half to the saddlebag side. If this is what is going on, then the fuel in both sides of the tank should pretty much stay equal until you run out. If the tank design team were on their toes, maybe they angled the center bump in the tank so that more fuel would run to the petcock side when it splashes up.
If your bike is sitting on the sidestand then the fuel would get trapped in the saddlebag. Under normal riding conditions my saddlebag is just as dry as the petcock side. If we are smart enough to see that one side of the tank is lower than the other, I hope the guys who designed the bike also picked up on that. Make sense? :)


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