Petcock function in prime.

[Rollo]

So i took the tank off my project bike with a gallon of gas or two in it. Had it set to "on" so no gas would come out. (which is still wierd to me cuz i'm used to working on my Harley which is gravity fed)

Figured i'd drain the gas by switching it to prime and letting it flow out.... but it didn't. Even when i tilted it toward the petcock. I could shake it back and forth and a little would come out. I'm thinking it's hosed... or was i supposed to open the gas lid maybe?

Did i mention i can turn the knob 360 degrees... don't think that's supposed to happen either. Maybe this has something to do with the hard starts and loss of power while on the throttle?

It's getting replaced. Just wanna know if it shoulda been flowing.

[cintidude04]

Shouldn't be able to turn the knob all the wy round... The fact that you can do that, to me, sounds like the plastic knob is stripped out an the petcock is stuck on one position. With loss of power on throttle it may possibly be stuck in the reserve position.

[Rollo]

Didn't think of that possibility. I'll check it tomorrow when i get back over to the bike. Nice that it's in another garage so it's not cluttering up mine but it sucks when you'd like to check something quick!

It should dump right out in "prime" position though right?

[mcssls]

yes

[scottynoface]

It sees the Harley, it wants to break down just looking at it

[Rollo]

funny thing is... the harley runs like a tank. the carb is like a tin can you dump gas and air in. why can't they all be that easy!!.... of course things may fall off along the way.... just don't ride directly behind one!

[Kreylyn]

The petcock uses a plunger with a spring behind it holding it "closed". This stops the flow of fuel. For fuel to flow, either vacuum is used to over come the spring and pull the plunger open (in the res or on positions when the motor is turning over) or it must be manually pushed open.

The prime position manually pushes the plunger open and holds it there. Under the knob is a plastic piece that has a curved ramp like slot. When you turn the knob towards prime it's like moving up the ramp... the surface gets closer towards the plunger. That surface is pushing on a "spring" clip inside the petcock. So you turn the knob, pushing the spring towards the plugner, which holds it open for fuel to flow.

The knob is half slotted, and the clip that holds it on has a matching slot. This system is what should prevent the knob from spinning more than 180 degrees. If the clip is broken or things are installed wrong, then you might be able to turn the knob more than 180 degrees.

If the knob does turn more than 180 degrees, then at the least you will have bent the spring that should push on the plunger inside so that it no longer will line up right to do that. Worst case is that spring is broken, and your probably looking at replacement of the entire petcock base to fix it.

See this thread for more details and pics of how to diassemble and rebuild the petcock.

http://katriders.com/vb/showthread.php?t=96553

Krey

[Rollo]

WOW! what a nice write up... i'll be pulling it apart today for sure.

First day of snow here and it's really coming down!!!!

[cintidude04]

And of course it took longer to get to work due to having to navigate around morons doing 5 miles an hour...

[Rollo]

Too bad your bike is down right now... you coulda zipped right past em.

This town is notorious for morons in the snow though... i'm guessing it's cuz we don't see all that much of it. Just enough to throw the curveball at people. When i was up in Michigan it was alot better because everyone got alot of practice!

If our snowfall this year is anything like our rainfall... everyone is gonna get better at driving in the snow.

[Rollo]

Back on topic... a quick glance after you told me what to look for revealed the knob turning problem. The clip with the notch in it was bent ( like \ instead of straight | ) so the knob would stop where it was supposed to toward reserve but push right past prime and on around.

Thinking i'll pick up the rebuild kit instead of a new one and just bend the tab back while ive got it apart. Thanks for the ideas.

[Kreylyn]

Back on topic... a quick glance after you told me what to look for revealed the knob turning problem. The clip with the notch in it was bent ( like \ instead of straight | ) so the knob would stop where it was supposed to toward reserve but push right past prime and on around.

Thinking i'll pick up the rebuild kit instead of a new one and just bend the tab back while ive got it apart. Thanks for the ideas.

You will need to remove the clip, the knob, and the plastic piece under neath to see the spring that is also bent (and making it so prime does not work now).

I suggest taking the diaphram out, and put the knob side parts together first when reassembly is happening to ensure you don't bend that spring again.

Krey

[Box746]

What is the "Prime" possition used for....

Why would I ever need to set the knob to the "Prime" possition....what would/should I be doing if I ever set the knob to the "Prime" possition..

The petcock uses a plunger with a spring behind it holding it "closed". This stops the flow of fuel. For fuel to flow, either vacuum is used to over come the spring and pull the plunger open (in the res or on positions when the motor is turning over) or it must be manually pushed open.

The prime position manually pushes the plunger open and holds it there. Under the knob is a plastic piece that has a curved ramp like slot. When you turn the knob towards prime it's like moving up the ramp... the surface gets closer towards the plunger. That surface is pushing on a "spring" clip inside the petcock. So you turn the knob, pushing the spring towards the plugner, which holds it open for fuel to flow.

The knob is half slotted, and the clip that holds it on has a matching slot. This system is what should prevent the knob from spinning more than 180 degrees. If the clip is broken or things are installed wrong, then you might be able to turn the knob more than 180 degrees.

If the knob does turn more than 180 degrees, then at the least you will have bent the spring that should push on the plunger inside so that it no longer will line up right to do that. Worst case is that spring is broken, and your probably looking at replacement of the entire petcock base to fix it.

See this thread for more details and pics of how to diassemble and rebuild the petcock.

http://katriders.com/vb/showthread.php?t=96553

Krey

[arsenic]

If you ever have the carbs rebuilt or the first ride after winter storage. There is no fuel in the float bowls. On these occasions, you would use prime to get fuel into the bowls.

[jak900]

In the middle of the small part is missing from a mine to get it?