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Hi Everyone

I need some help. I have an '86 GSXR 750, old slabside. The petcock has four settings:

RES I assume this to be Reserve
PRI I assume this to be Primary
FUEL
ON

I'm not sure about RES and PRI, but my problem is, I dont know which one to run on. Also, how can i turn fuel flow off?

I'll take any info

Thanks in advance

I believe the setting should be to on..

When you start to run low you switch to PRI then to RES. Then after you fill up to run in RES then switch to PRI then back to ON..


Can someone confirm this is correct?

Usually this type of petcock only flows fuel when the engine is running (vaccuum operated). The PRI(me) position is to flow gas to the carb when the tank is completely empty to enable starting the bike. There is no OFF position.

Would it be a good idea to install a simple cutoff valve in the fuel line so that I can easily turn off fuel flow.

My biggest concern is that I want to run all the gas out of my carbs when I let it sit.

Thanks for previous, and future responses.

'Pri', or Prime, uses a plunger inside the petcock to open the valve and allow fuel to flow without the engine running - no vacuum required. You only use this setting if you have drained the fuel out of your carbs for removal/cleaning/storage/what have you in order to refill the float bowls. you only need to have the petcock switched to Prime for a few seconds, then switch it to 'On'

If you leave the petcock on the Prime position for too long you will overfill the carbs and you will start leaking fuel out the carb vent line and possibly the airbox drain.

'On' is the normal operating position - this draws fuel from a taller pickup tube inside the tank. When your bike starts to cough and sputter, you switch the petcock to the 'Res' position - this draws fuel from a shorter pickup tube in the tank, allowing you to use the fuel in the bottom of the tank to get you to the next gas station.

After you refuel, remember to switch the petcock back to the 'On' position; if you leave it in the reserve position, the next time you are riding and it starts to run out of gas, you really will be running out of gas and will be pushing the bike to the next station.

For a petcock like this with no 'Off' setting, the simplest way to cut off fuel flow to the carbs in order to run them dry is to leave the petcock in the 'On' position and disconnect the vacuum line from the petcock (or the engine, if that is easier to get at)

Remember to plug the vacuum line with something ( a wooden golf tee works well) or your engine won't run very well (major vacuum leak)

This is what I done on my Gs500 I had res Pri and on.I done away with the petcock and ran a line striaght from the Res in the tank to the carbs I also put a standard on and off value to turn off the fuel.It works great the one thing I know I get 55 mpg have a 4 gal tank so I use the trip and refuel at 175 miles or so.It works great and is simple.

If you leave the petcock in PRI and you start getting leaking out of the carbs, then you have faulty floats or needle valves in the carbs.

You shouldn't have to worry about this.