Gas Tank Questions

I have two quick questions pertaining to the gas tank on a 1986 Yamaha Maxim XJ700.

1) The petcock only has a PR, ON, and RES. I'm assuming that's prime, on, and reserve. How do I turn it off so it wont flood?

2) What is the plug/valve thing in the middle bottom of the tank near the back that screws in?

 

I don't know much about 700's, so no idea about #2.

There is no Off on the Petcock, you are correct with On, Prime and Reserve.
On is for normal operation and is vacuum controlled when functioning properly. This means no fuel will flow when the bike is not running (= no flooding).
Prime is for when you need to fill you carb bowls and the bike is not running, this by-passes the vacuum control and the fuel will flow non- stop out of the tank. (= no flooding). But if the fuel flow isn't restricted why no flooding? Because with your floats and float valves set properly when the carb bowls fill to their in-spec height the valve closes and no more fuel will enter.
Reserve is for when you are running down that long road and forget to watch for gas stations, the fuel will stop flowing when the level gets too low while in the On position, switch to Reserve and you get an extra 1/2 (?) gallon of fuel to use. I am sure someone else here will chime in with the exact reserve amount.

I'll take a stab at #2 - fuel level sensor?

 

Stumpy's got you on #1. Do you have a picture for #2?

 

looks like a canister hooks up if this is your tank.
https://www.shopyamaha.com/parts-ca...MOTORCYCLE)/FUEL_TANK_XJ700SC_(XJ700S_-_1986)


valve is listed as
20K-24180-00-00 ROLL OVER VALVE ASSY

 

^^That^^ you have emissions equipment on that machine (or what's left of it).

 

Thanks everyone!! Really glad I don't have to worry about flooding it by just leaving the petcock on all the time. And you're right about the little check valve thing. It just goes to that stupid can thing.

 

The stupid can thing that helps the air stay clean enough for breathing purposes. I like those stupid can things because I remember the smoggy summer days of the 70's.
Still, one less evap canister on an old bike isn't going to cause too much harm.

 

I you have a place for a tube to attach to the underside of your tank, then you have a california emissions tank. If you have a california bike, then you should have a canister under the right side body cover. A hose comes off of the carbs to it, and a line to open air, and the vapor line to the tank.

Dave F

 

Yeah, that's what I have so it must be California emissions compliant.