Petcock/Fuel Flow

bpd106

XS650 Enthusiast
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I know this may be a dumb question, but on the petcock of my 81 XS650 Special II, it has 3 designations on it.."Reserve", "On", and one that is marked "PRI". 2 of them are self explanatory but what is the "PRI" designation?
If the petcock allows fuel flow in the "PRI" location, when do you run it in that position?
Sorry, I've already tried to look it up and had no luck. I don't have an owners manual, only service manuals.

Thanks!
 
I was also looking for info on this and also, What position would this be left in if bike is not to be riden in few days??
 
pri is prime for when you worked on your bike and the carbs are empty - flows freely no vacuum needed. on is normal running.

prime flows on reserve levels or normal levels both - a good reason not to use it for normal running.

when there's no vacuum, on and res is automatic off, as if you'd turned it to an off position.
 
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