Petcock "off" position?

Could be dumb question, but you all are always very gracious! A buddy of mine and I were pulling the gas tank off my '85 XJ700N to work on the carbs. He has an FZ1 and said, "First, turn the petcock valve to 'off'." We quickly realized we had no way on the XJ to stop gas from pouring out the main and prime outlets when we pulled the hoses off. Sure enough, we pulled them off and had gas running out everywhere and had to find a ballance between tipping it up enough to keep gas from flowing out of the valves, but not too high so as to leak out the gas cap. What do u all do when pulling the tank? Do I really need to drain all the gas out every time I pull the tank? Thanks!

 

sounds like you need to rebuild the pitcocks.

 

You should have ON-RES-PRIME & it's where the LEVER points.

 

I think you've got the typical XJ petcock! It has 3 positions, ON, RES, PRI. It also has an INLET (from tank), OUTLET (to carbs), and VACUUM line (from an intake boot). ON flows fuel only when there is a vacuum signal from the VACUUM line (engine is running). PRI flows fuel without the VACUUM signal. RES operates like the ON (I think), but draws fuel from a lower position. I actually don't remember if PRI draws from from the High or Low level in the tank. If the fuel flows in the ON position, then something is wrong with the VACUUM side, maybe even parts are missing (if someone rebuilt it incorrectly). ON is actually "OFF" when the engine is off. Fuel shouldn't flow out the VACUUM line.

There is a great picture somewhere that shows the fuel flow, but I can't find it.

Great rebuild thread by BigFitz52 here: http://xjbikes.com/Forums/viewtopic/t=2 ... build.html

 

Correct. Both ON and RES are supposed to be off unless there's a vacuum signal; no fuel should ever come out of the vacuum port. If you've got fuel flow in anything other than PRI and/or gas coming out the vacuum line, then you've got a completely failed petcock.

 

These XJ petcocks are unreliable & prone to failure. & they aint cheap to buy new! I didnt know thats there is a rebuild kit for them til after my 3rd one. You can probably find where to get a rebuild kit by searching around this forum. I dont trust mine, so when I pull my tank off I use a short length of extra fuel line with a bolt for a plug at one end & attatch it to the petcock fitting. Just make sure the plugged end isnt leaking.

 

I know RickCoMatic recommends putting a Briggs and Stratton style inline fuel shut off to make sure the fuel is off.

I don't think you will have ANY issue with a petcock if you rebuild it according to BigFitz52's How To. He'll have you polishing the inside so the seal is PERFECT and UNCOMPROMISED. Also, chacal has the rebuild kits and parts info you need.

 

I've often wondered if the high ethanol content in gasoline has been a problem eating the seals in my petcocks. I sure have had bad luck with new ones I've bought. Not had any probs since the rebuild tho. Maybe they upgraded the materials in the seals or ? Anyone have an idea?

 

Thanks, all! Great advice. I will try it.

 

For those with petcock problems...check some Kawas (Ninja ZXR 250) has the exact same petcock working exactly the same ON/RES by vacum signal while the engine is running and PRI as a free fall of gas to the carbs with the engine running or not.
Rod

 

That's because the manufacturer, Taiyo Gaiken, provided/provides petcocks to a number of different companies, not just Yamaha.