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dumb question!

  • Thread starter Thread starter dcn32459
  • Start date Start date
D

dcn32459

Guest
im very new to bikes!! so dont laugh... ok laugh...
anyway on the petcock what do the positions mean? i know what reserve is , but prime? and where is off?
 
prime means that fuel flows all the time, not just when the bike is on or the engine is running -- it's used to 'prime' the carbs for cold starts or if the bike has been sitting for a long time.

you're 'on' or 'run' is essentially also your 'off' position, as fuel will only flow when the engine is running.
 
The "normal" position for the petcock is ON. It is controlled by engine vacuum. When the engine is running, it supplies vacuum to the back side of the petcock and opens the valve. When the petcock is working normally, it shuts off when the engine is off.

If you have not been riding for a while and the carbs may have evaporated a bit, use the PRIME position while you get your helmet and gloves on, then start the bike and move the petcock back to ON.

The ON position draws fuel from a tube that sticks up in the bottom of the tank (on top of the petcock) about 2 or 3 inches. When the fuel level gets to the top of that tube, your carbs run dry and you have to move the petcock to RESERVE. The RESERVE position draws fuel from the bottom of the tank, and it is usually about one gallon. If you know the size of your tank and how far you have just gone on the first few gallons, you can guess how long it will be before you are pushing the bike to a gas station. 8-[


By the way...it's much dumber to NOT ask the question. Now you know the answer. \\:D/


.
 
thanx

thanx

well that definatly helps !! i bought the bike today and when the guy started it for me he put it in the prime pos. and the choke all the way on... the bike started and reved at to 5k , after shutting the bike off we couldnt start it again. he said it was flooded. when i got it home and took it off the trailer i tried to start it and did just he did .. would not start.
so now its in the on pos. , hopefully it will start tomorrow. i think the carb needs rebuilt anyway.
 
dcn32459 said:
well that definatly helps !! i bought the bike today and when the guy started it for me he put it in the prime pos. and the choke all the way on... the bike started and reved at to 5k , after shutting the bike off we couldnt start it again. he said it was flooded. when i got it home and took it off the trailer i tried to start it and did just he did .. would not start.
so now its in the on pos. , hopefully it will start tomorrow. i think the carb needs rebuilt anyway.
Click to expand...

Post the year and model of your bike, it helps you get the info. you need.

When starting a GS, just use the choke. Do NOT open the throttle while trying to start it, it nullifies the choke.

Most of these bikes rev. pretty high when started on full choke. Be ready to push you choke in quickly once the bike starts to control your revs. Use the throttle once it starts to warm up a bit.
 
Eventually you will find the "sweet spot" on the choke where the engine only goes to 1500-2000 rpm and sits there idling happily, waiting for you to finish putting on your helmet and gloves.

I makes me cringe when I hear a bike (or any engine, for that matter) rev that high so soon after start-up. :shock:


.
 
Steve said:
I makes me cringe when I hear a bike (or any engine, for that matter) rev that high so soon after start-up. :shock:
Click to expand...

Me too Steve. I feel like running over and hitting the big red emergency stop button (like in petrol / gas stations). LOL

I live near a river and every weekend I listen to people start up their boats and rev the absolute crap out of them as soon as they start. It's no wonder the engines die so soon.

*Oil pressure people, oil pressure*
 
Had the same problem figuring out the shutoff pos.

Had the same problem figuring out the shutoff pos.

I bought a 78 GS550 last summer and on the pitcock there is th on position,reserve, and I could not figure out what pri meant. I could not figure out which postion to use to shut the fuel off when parked. So from reading the posts on this question my understanding is that to turn the fuel off when parked is to set it to the on position?
 
78550Detroit said:
I bought a 78 GS550 last summer and on the pitcock there is th on position,reserve, and I could not figure out what pri meant. I could not figure out which postion to use to shut the fuel off when parked. So from reading the posts on this question my understanding is that to turn the fuel off when parked is to set it to the on position?
Click to expand...

Correct. there is a vacuum line that runs to your petcock as well as the fuel line. When you start the bike, vacuum from the motor puts a suction on a diaphram thing that allows gas to start flowing to your carbs. Reserve is the same way except that on reserve you can use all the gas in your tank.

So when your petcock is turned to "on" or "run" it is off when the bike is not running and on when the bike is running if everything is working correctly.

On "prime" gas is always flowing to the carbs even when the bike is off, so that if the bikes been sitting for a while you can get some gas in the carbs before trying to start it. When the bike is off, you shouldn't leave your petcock on prime as gas may leak past your float valves and into your engine.
 
Last edited:
I don't think the petcock should have been left in the prime position while you were trailing it home. I think gas can make it's way into the crankcase if it's left on prime.
Eddie V
 
now that im used to my bike i get the petcock now ! my reserve works much better as a primer lol...also i bought a new clear fule line, all i can say is EVERYONE should have a clear fule line !!!
makes life so much better ..lol just look down and say "yep its gettin gas".
 
eddiev said:
I don't think the petcock should have been left in the prime position while you were trailing it home. I think gas can make it's way into the crankcase if it's left on prime.
Eddie V
Click to expand...
yeah i agree there!! could be the reason i now have a bad oil leak from my crank case cover :(
 
dcn32459 said:
yeah i agree there!! could be the reason i now have a bad oil leak from my crank case cover :(
Click to expand...

Be sure to check what your oil smells like. If you get even the slightest whiff of gas from it, change it and the filter before running the motor again. Gas in the oil can cause all sorts of problems.
 
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