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Viking
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Discussion Starter #1
Might be a dumb question, but I read about turning the fuel switch to "off". My swich has 3 positions, on, reserve and prime. How to turn this off? When to use prime....
 

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there were 2 different petcocks used during the 20 year production run of the VN750. Earlier models had a prime position instead of an off position.

Your model year did not have an OFF position. The vacuum line on the bottom of the petcock from the left carb only allows fuel to flow when running by applying vacuum to the valve which opens the fuel flow.....assuming it is working properly.

EDIT: I assume PRIME is used when the carbs are dry....or it can be used if you need to drain the tank
 

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Is this a vulcan 750? Mine has 3 positions, ON, OFF and RESERVE. Never heard of Prime. Unless its an older model or the petcock has been replaced before. This fuel system has 3 lines that go to the fuel tank petcock. One for each carb and the other is a vacuume line. For fuel to flow to the carbs a vacuume has to be felt on the vacuume (center) line.
thanks KC I guess I was typing this the same time you were.
 

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1986 VN750
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Is this a vulcan 750? Mine has 3 positions, ON, OFF and RESERVE. Never heard of Prime. Unless its an older model or the petcock has been replaced before. This fuel system has 3 lines that go to the fuel tank petcock. One for each carb and the other is a vacuume line. For fuel to flow to the carbs a vacuume has to be felt on the vacuume (center) line.
thanks KC I guess I was typing this the same time you were.
"PRIME" is on the the older models (85-87 I think), and was removed / replaced by "OFF".

I loved the prime option. Helped drain most of my tank!
 

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Haven't looked that closely at mine but noticed that the off position is not in the center, found out the hard way that towards the rear of bike is off position.LOL:doh:
 

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romeobravo172
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842 Posts
Handle to rear--off
straight down--on
straight forward--reserve
 

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romeobravo172
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Try practicing switching from on to reserve till it becomes second nature, Will save you time sitting on side of road, cranking& cranking to get fuel back in carbs. The petcock is controlled by vacume to let fuel flow to carbs!
 

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If only it had 6th gear..
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Yeah the prime is useful for... well, priming the carbs after storage or running out of gas - never happened to me ;-) and it saved your starter and battery undue stress. Guess it wasn't cost effective to have 4 positions when they incorporated the off position.
 

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Mine must be hooked up backwards as I have to leave mine on prime to run the bike, All the way forward is reserve for me still and straight down is off. This is only on my bike though which makes me think someone crossed up the fuel lines or something.
 

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If only it had 6th gear..
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Even if they did it would still work. The 2 fuel hose fittings go in to 1 channel. Sounds to me like your valve has a clog.
 

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Thanks, I guess I need to get in there and do some cleaning. I didn't really want to mess with it, but I will go on and clean it. Will it hurt anything running it on prime. Just curious?
 

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Thanks, I guess I need to get in there and do some cleaning. I didn't really want to mess with it, but I will go on and clean it. Will it hurt anything running it on prime. Just curious?

The only problem running on prime would be if either of your carbs floats got stuck open, it would flood the motor with fuel. Gas in your oil would be bad.

You can always try pulling off the fuel line and just blowing through it. If you hear bubbles inside the tank the lines clear.

Make sure to use a long length of hose, and have the open end ABOVE the gas tank.
 

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If only it had 6th gear..
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Thanks, I guess I need to get in there and do some cleaning. I didn't really want to mess with it, but I will go on and clean it. Will it hurt anything running it on prime. Just curious?
just be careful with the screen that is on the upper section of the petcock and sits inside the tank. some are brass and some plastic but both may be brittle. I cleaned up mine with a pipe cleaner. you may want to just buy a rebuild kit on ebay. I don't think they are all that expensive. I would probably just drive it on prime until a rainy weekend came around, and just move it to ON when you're done riding, which in this case would be turning it off ;) because even if you have a small leak in one float that maybe isn't noticeable when it's running, over time you'll contami'minate your motor oil. Hope that helps



Hmm, just thought of this. In both positions ON and RES the bike won't run? That tells me that your vacuum valve isn't opening. Simple test is to check your vacuum line going to the left carb.If it l looks good and you are getting vacuum, there is a plunger and diaphragm in the petcock and it's probably stuck closed so you really might want a kit for it. Peace.
 
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