Petcock...On or Pri?

Yes, I know this is a totally newbie q's. But while I was riding my newly acquired xj650, (few miles into the road), it started to sputter. I have enough gasoline in the tank. And the bike died. I switch it to RES, and ON and PRI and attempted to start the bike. I left it at PRI and it's running again, no problem. Yet.

The recent work that I did was installed an in-line filter. And the petcock was working(ON no flow)....when I tested it(when I cut the fuel line to install the filter).

Anyways, petcock ON or PRI?

 

"ON" for most situations
"RES" when you need that last couple quarts to get to the gas station.
"PRI" only to fill the bowls when the carburetors have been drained.

"PRI" runs fuel all the time. It draws from the bottom of the tank just like "RES" so when you run out on "PRI" you're done.

"ON" and "RES" should only flow fuel when there is engine vacuum.

If it runs on "PRI" and not "RES" you should suspect a problem with the vacuum line or the valving in the petcock.

 

Thank You!
So the bike will run maybe a few miles with the petcock @ON position then sputters. I rode it to work with the petcock @Pri postion and it was fine.

Is there any danger/damage if the petcock is left at @Pri position all the time? Seems like my bike likes to run on the Pri. Perhaps it's not a good thing due to gas evaporating and will absorb water?

I suspect that the gas cap is the culprit(a little wobbly/loose).

 

You could have a plugged gas cap vent but it is more likely that Carl hit the nail on the head. A loose gas cap won't cause your symptom. You most likely have a cracked or split (or loose) vacuum line or the petcock needs rebuilding.

Danger if the petcock is left on PRI: While riding, very little. While stopped, NOT GOOD. If you were to experience a stuck float with the bike off and the petcock on PRI, it can fill the crankcase up with gas.

Until you get your petcock fixed (do it soon) you can ride on PRI and then turn it to ON when the bilke is shut off, and hopefully the valve is working well enough to stop fuel flow.

 

If you're sure you have enough gas in the tank, then Carl is probably right--you should check for a vacuum leak or a problem with the petcock itself. Bear in mind that your bike's fuel tank tends to go to the "reserve" level earlier than you might think it should. Even if it looks like there's plenty of gas in there, it may not be enough to feed the beast with the petcock in the "on" position. Whatever you do, NEVER leave the petcock on "prime" while the bike is sitting. You'll wind up with a crank case full of gasoline and a big mess to deal with.

 

Dammit, Fitz! You stole my thundah!

 

Good point. They still look pretty full when "RES" is needed.

 

ahh...thanks guys! That's what probably what happened. I pour 1.5 gal of gas(after draining all the old fuel) just to test ride her. It ran for few miles then it quit running.
I turned it to Pri and it ran again.

Last night, I filled her up with gas. This morning, I rode the bike to work (4miles) with the Petcock to ON and never had any sputtering/problem like the old symptom.

I was thinking of a clogged fuel line but the bike ran, so I can probably eliminate that.

Thanks for all the inputs, you guys are very helpful. I'll keep you posted.

Rod

PS, I'm going to turn the petcock to ON right now. (it's been like that for the last two hours).