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On the fuel tap there is 2 positions; On & PRI(Prime). The owner's manual says it's not supposed to be in the "PRI" position while riding but I checked mine today and it was in the "PRI" position. I moved it to the "On" position. Anybody know what it's supposed to be on and what the difference is between the 2?
 

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On 'Prime' fuel flows directly to the carbs from the reserve position on the tap. With the bike stopped there's a chance that fuel will continue to flow and flood the carbs and the motor. It's meant as an emergency position to start the bike when the carbs are dry after it's been unused for a few days.

On 'On', fuel only flows when the engine is running and shuts off when the engine stops. The tap should normally be set to 'On'.

There should also be a third position for 'Reserve', unless you bike is fitted with a low fuel warning light. Reserve gives you access to enough fuel to get you about another 20 miles or so after it appears to have run out on 'On'.

Rob
 

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So you are correct. 2 positions. The petcock is what's referred to as a "vacuum operated" petcock. When the engine is running (and vacuum is created in the intake) it pulls a diaphram in the petcock opening it. As soon as you turn the engine off and vacuum is lost the petcock closes.

So while it is on the "on" position, your petcock self-closes. The other position bypasses the vacuum diaphram and locks the petcock open. This is useful for priming your carburetors (hence the PRI marking) if the bowls are completely dry, or draining your fuel bowls. There really isn't any need to have the pickup on PRI unless you've worked on your carburetors. Even after sitting for an extended period of time a couple of extra cranks of the engine to open the petcock is all it takes to refill the bowls.

There aren't 2 difference level pickups inside the fuel tank as with older 250's so once you're out of fuel, you are OUT. There is no reserve.
 

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Paul

Hi, when i run my bike on prime it runs great.Plenty of power and doesnt miss a beat.When i turn the fuel tap to the on position it starves itself of fuel and cuts out.I know the prime position is for filling the bowls after a carb strip down and if left on prime it will flood. So why does mime starve itself when in the on position ?
 

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Hi, when i run my bike on prime it runs great.Plenty of power and doesnt miss a beat.When i turn the fuel tap to the on position it starves itself of fuel and cuts out.I know the prime position is for filling the bowls after a carb strip down and if left on prime it will flood. So why does mime starve itself when in the on position ?
Sounds like your petcock is worn or your vacuum connection is bad. I would check your connections and if they are good get a replacement petcock or maybe a rebuild kit if available.
 
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