Fuel Petcock

My petcock only seems to let fuel out on PRI. I have cleaned the screen. So there are three positions----res----pri----on. where is off? and is running it on pri all the time okay? will that cause problems? new petcock 150 bucks locally. Parts are expensive for this machine. sheesh.

 

Off is "On" when the engine isn't running. These petcocks are vacuum operated: engine vacuum, applied from one of the carb holders through a vacuum line to the petcock, opens a diaphragm and lets fuel flow when the engine's running. When the engine stops, the fuel flow is automatically turned off. This is mainly for safety.

I have a running disagreement with other members on this forum, though, as to whether running in "Prime" should be OK. The concensus, which I do not share, is that prime will always overflow your carbs. My belief is that incorrectly adjusted float height, or badly sealing float needles, will cause your carbs to overflow if left on prime, but may still see your carbs overflow when running in "On."

Overall, though, best thing would be to make sure your vacuum line to the petcock is correct, and, if needed, disassemble and clean the petcock to help restore correct function in the "On" mode.

 

I have a similar problem. My petcock has a vacuum leak. So I pulled the vacuum line off the bike and capped it at both ends. So now when I shut the bike down. I turn the petcock to “ON” which is off without a vacuum. Then turn it to “PRI” before I start it. I grew up with old dirt bikes that didn’t have automatic petcocks anyway. So this is normal for me. I intend to rebuild it one of these days. Just not that big a deal to me.

One more thing, “RES” needs the vacuum to operate. So do use it.

“PRI” draws for the same pipe as “RES” so it is the same as reserve anyway.

 

I had the same problem, but I just rebuilt my petcock with a few bucks worth of parts from Chacal. Now everthing is perfect.

 

Your petcock needs a Vaccum to be operated in the ON position. Now if you've got the gas tank off and you've put it in the ON postion and no gas leaks out, thats good. when you attach it to your bike and let it run it should suck gas right into your carbs.
Pri is for priming your carbs, like after cleaning them or when you run the bike completely dry.
If you're driving and you feel your efforts on the throttle are in vain and she starts to die on you by "sputtering" and jerking, that means you're running out of gas. Reach down and turn it to RES.
All three of these have different, very important functions.
I'd drain your gas out, turn your tank upsidedown on some cloth or something, and remove that petcock and see whats up if the above doesnt help. Its Usually your VAC diaphram. Cheap fix. like twenty bucks for parts and shipping. Get yourself a selector lever O-ring and a vac diaphram plunger and gasket if it looks sad in there.
-SLKid

 

Should be able to test this.

Petcock to on for duration of test.

Pull the fuel line on the carb end. Stick it in a bucket. Start the bike (it will run for a short time without fuel delivered to the bowls. See if fuel comes out the hose. Assuming it doesn't, shut the bike down. (If it does, problem is not fuel delivery system.)

Get a syringe and attach it with a stubby piece of tubing to the vacuum port on the petcock. Apply vacuum to the port by pulling the plunger. If fuel flows, then problem is in hose or connection. If it doesn't then its the petcock. Parts and rebuild (or at least disassemble and clean), they really are simple devices.

If it flows, check same way only using your vac hose instead of the stubby one. If it doesn't flow its the hose (it may be 26 years old). Other wise, the problem is the connection with the carb. Try the port on a different one.

 

yes, i fugered this all out last night when i finally got the carbs to stop leaking and the floats adjusted correcty. i understand the vacuum function. I have already replaced the hose to the carb from the petcock. The petcock is working but leaks at the selector. ill have to take it apart. thanks!!!!

 

Great, another problem solved now whats next...