I have a 87 lt80 that I recently bought and rebuilt.  One of the problems I have with it is that gas is leaking thru and filling the crankcase/cylinder.

I have a carb rebuild kit on the way and hoping that a new needle and seat will cure the gas seepage.

My question relates to the gas valve, there does not seem to be a off position.  It looks like reserve when turned backwards, when vertical, gas flows when the engine turns, and all the way forward, gas constantly flows constantly, but there does not appear to be a "off position".

Also, there are two lines running to the carb from the tank, one enters the carb at the normal spot, the other at the top of the carb, what is the purpose of the second line?

there is no off position on the petcock. 1 fuel line feeds the carb the other is a prime line to the intake. most likely your problem is the petcock not the carb. go to your local yard tractor repair shop and get an inline fuel shut off. did this on my sons lt80 and it has worked fine. just remember to shut the fuel off when done riding. a replacement petcock is about 40 bucks the fuel shut off about 6 bucks. good luck

Go to LT80 HopUps http://midwestmini.c...t80_hop-ups.htm and order a new pet cock with only one line.  It does away with the vacuum port and provides an off position.  Then cap off the vacuums nipple on the carb.  Mine leaked into the crank case as well.

What kind of ATV is this??? Why would the manufacturer make it so there is no off valve? Sounds like cheap faulty manufactring to me... if there is some kind of logical reasoning behind this bizarre design please let me know...

The petcock is supposed to automatically cut off when the engine stops.  it opens on vacuum from the carb.  Failure seems to be a common problem.