Newbie here, petcock question...

[grabberblue]

Hi, I am new to forum (and to XS11's) and I just got my XS11 a week and a half ago. It is a '80 G with 93,000 miles and runs fine. The one thing that puzzles me is the petcock. The guy I bought it from says that the guy before him that owned it said the petcocks were messed up so just leave them on PRI. I noticed they have 3 positions, PRI, ON, and RES. When I leave it on PRI sometimes the gas leaks out of the carbs (this explained the lousy gas mileage) Is there an OFF? Please help and explain the function of this puzzling petcock.
Thanks in advance.....

[rneal55555]

ON is off so is reserve. The petcocks were designed to be vacum operated they are supposed to shut off them selves when the engine is turned off and intake vacum goes away. PRI is designed to be used when it is neccesary to fill the carbs such as after a rebuild/cleaning or anyother time the bowl is drained. They should be run in the on position although even that does not garantee they won't leak. If you still have the leak problen with them in the on position there are fix it how toos in the tech tips.

[xssiveone]

Is there an OFF? Please help and explain the function of this puzzling petcock.

No off postion. And there's really nothing puzzling about them, this design is very common on m/c's.

The PRI is for PRIME, gives you a free flow of fuel from the tank, very usefull for filling up the carbs when you've just replaced them after cleaning, or for those more embarrasing moments when you've miscaculated your fuel range.

ON is, well, ON and should be used for normal day to day operation. This position draws from the main part of the tank.

RES is for RESERVE, which draws from the bottom inch or so of the tank. This gives you about 35-40 miles until you need to start pushing. See above comment about miscalculating your fuel range.

The petcocks have a built-in shut off valve. The engine vacuum pulls a diaphram back which has a piston in the center that opens or closes the petcock. No vacuum, no fuel flow. Of course, this is in a perfect world and assumes that the petcock is functioning, which you've already stated that this isn't the case. Petcock repair kits are readily available and I highly recommend you purchase and rebuild your petcocks.

The second thing you should be looking at is a carb clean at best, or new needle and seat assemblies at worst. The float valves (needle and seat) are also supposed to stop the flow of fuel when the float bowls get full. If you're got gas leaking, then one or more are not doing their job.

And, finally, since you had gas leaking, you should check your engine oil for gas contamination. When petcocks leak, and the needle and seat fail, it's quite common for the gas to flow into the engine and into the oil. Gas contaminated oil is very hazardous to your engine and should be changed immediatly.

[grabberblue]

Thanks for the replys, My previous Bikes were 73 Honda 350F and '71 750F, both had ON, RES, and OFF.
I took my tank off a week ago and did not see anything like a vacuum line does it go to the tank or the carbs?

The gas was leaking out of the #4 carb, thanks, I was thinking the needle and seat should shut it off, now you have made me feel better about getting a kit to rebuild.

[John]

There should be a small vacuum line leading from the nipple of #1 & 4 carb boots and connecting to the corresponding petcock. That is the vacuum supply for the petcocks. There is another smll hose leading from the CARB body on #2 carb. It is the vacuum source for the vacuum advance unit under the left side cover of the engine. The float seat assemblies have an O ring sealing them from the carb . They can leak also, and that will flood the airbox, and dump fuel into the crankcase also. When you take the floats out, check to see if they aren't sinking from being too heavy, and not rising up to seal off the fuel flow.

[xssiveone]

Originally posted by grabberblue
I took my tank off a week ago and did not see anything like a vacuum line does it go to the tank or the carbs?

This is certainly part of the problem then. As John indicated, there should be a vacuum line going to each petcock. Maybe you'll get lucky and it will be this simple for the petcocks.

As for the "kits", you probably don't need a complete overhaul. Try a good cleaning first, and then if that fails, replace the needle and seat in the leaking carbs. I haven't checked recently, but there was someone selling needle/seat sets on Ebay quite regularly. Be careful if buying K&L kits as the jets are the wrong size.