Petcock Issue

SilverTalon · Mar 18, 2012

Hey guys,

So I finally had the carbs put back on and took the bike out for my first day of the season. For some reason if I have the petcock on "on" or "res" it won't fuel the engine. If I switch to "pri" it works fine.

Is there something I can check out to see what the issue is, or is it going to be very complicated?

drewpy · Mar 18, 2012

vacuum diaphram not working or disconnected somewhere via the inlet

SilverTalon · Mar 18, 2012

drewpy said:
vacuum diaphram not working or disconnected somewhere via the inlet

You wouldn't happen to have a picture of what I should be looking for do you?

drewpy · Mar 18, 2012

no, all mine are connected. the vacuum pipe will be the easiest to check. It runs from behind the tap, over the frame spine and to the right side inlet. just check for splits and connections.

the petcock will need stripping so you may as well buy a repair kit before hand, if the vacuum pipe checks out ok!

ace68 · Mar 20, 2012

quick check. disconnect the fuel line,disconnect vacuum line off carbie and give it a suck
if fuel doesnt comes out vacline is pinched or cracked ,probably.

OliverB · Mar 20, 2012

The vacuum actuated plunger in the petcock can also stick in the seat of the petcock if there is corrosion. A messed up seat can also result in the o-ring of the plunger not seating properly when the bike is shut off and fuel leaks into the carbs and runs into the air box(es). I'm having that problem with the one on my '79 now.

SilverTalon · Mar 21, 2012

When we had the tank off, the fuel would leak through the left side tube, but not the right side.

I'm not the proficiant with fuel lines. For now will I be able to ride with the switch on prime?

Again, worked before we Took the carbs and tank off

HoughMade · Mar 21, 2012

I'm a little unclear. The petcock should have one tube going to an intake boot to supply engine vacuum to the petcock that simply pulls a valve open. The other tube should supply fuel to the carbs. Which is the left and right? Fuel should only come out one.

xschris · Mar 21, 2012

Can you post some picks? Like to see what you have

SilverTalon · Mar 21, 2012

xschris said:
Can you post some picks? Like to see what you have

Will do tonight

ace68 · Mar 21, 2012

SilverTalon said:
When we had the tank off, the fuel would leak through the left side tube, but not the right side.

I'm not the proficiant with fuel lines. For now will I be able to ride with the switch on prime?

Again, worked before we Took the carbs and tank off

Yes you can ride in the prime position,you may have connected the lines wrong.

HoughMade · Mar 21, 2012

SilverTalon · Mar 21, 2012

xschris said:
Can you post some picks? Like to see what you have

Attached are pictures, sorry about the quality

xschris · Mar 22, 2012

I think it just needs to be taken out and rebuilt.

SilverTalon · Mar 22, 2012

HoughMade said:

If my petcock is setup like this, I don't think there is anything plugged into the vacuum spot right now.

But I don't know if there was anything plugged in before, or if there was, I'm not sure where to reconnect it.

HoughMade · Mar 22, 2012

If there is nothing hooked up to the vacuum, it will only run on PRI because in the ON position, vacuum is supposed to pull the valve open.

There is supposed to be a tube from the smaller barb on the petcock to a barb on the carb holder, which is this:

...and is located right here:

It only needs to be hooked up to one carb inlet, right or left, doesn't matter. However, whichever one you don't use, make sure you cap it so air cannot be drawn in.

If you get that hooked up and it still does not work in the ON position, well then, yep, a petcock rebuild is in order.

SilverTalon · Mar 22, 2012

HoughMade said:
If there is nothing hooked up to the vacuum, it will only run on PRI because in the ON position, vacuum is supposed to pull the valve open.

There is supposed to be a tube from the smaller barb on the petcock to a barb on the carb holder, which is this:

...and is located right here:

It only needs to be hooked up to one carb inlet, right or left, doesn't matter. However, whichever one you don't use, make sure you cap it so air cannot be drawn in.

If you get that hooked up and it still does not work in the ON position, well then, yep, a petcock rebuild is in order.

just need to wait for it to cool off and then I can take a look

SilverTalon · Mar 22, 2012

SilverTalon said:
just need to wait for it to cool off and then I can take a look

TLDR=

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Ok fellows, here's the update.

Stupidly, I did not have the vacuum line hooked up to the petcock. I hook it up, things run great, better than without. Then after a bit I stall out.

"SHIT!" I think, must be the battery again. Except the lights aren't having an issue. So I get it started again and the bike begrudgingly brings me down the street.

After more trouble, it seems to be working better, so I give it another test, going down the street. I stall yet again.

I try starting it, auto and kick, for about 5 minutes, get it slowly going again. It again begrudgingly takes me home.

I immediately got my multimedia out, and the battery is fine. I'm assuming I kinked a line somewhere. Would it behoove me to replace the fuel lines, which have probably never been replaced, before completely redoing the petcock?

On top of that, has anyone recently bought tubing, and knows what sizes to buy? 1/2" for the fuel, 1/4" for the vacuum?

SilverTalon · Mar 23, 2012

so I put a new fuel line in, new vacuum line, and a small filter.

Hopefully it works out better tomorrow. Haven't tested yet.

HoughMade · Mar 23, 2012

Looks good to me.

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