Petcock setting and fast idle

[777jfk]

When I bought my '79 XS 1100 Special a month ago, the previuos owner told me he always ran the bike with the petcocks set to PRI and never used the ON or RESERVE. I tried running the bike in ON and it starves for gas but it runs prefectly fine on PRI. The only issue is on some days, the it will idle at about 2500 RPMS. Normally it idles at about 500 to 800. Has anyone experienced this issue or have any suggestions?

777jfk

[cywelchjr]

Sounds like you need to rebuild the petcocks. That and make sure that the vacuum lines to the petcocks are not leaking as they can cause both problems.

Also the fast idle may well be caused by the bike needing a good sync, which includes setting the idle mixture, which from the sound of things might be too lean. Also 500-600 RPM idle is a bit low, these things were intended to idle about 1100 - 1200 RPM.

[foreda]

Petcocks

When I bought my '79 XS 1100 Special a month ago, the previuos owner told me he always ran the bike with the petcocks set to PRI and never used the ON or RESERVE. I tried running the bike in ON and it starves for gas but it runs prefectly fine on PRI. The only issue is on some days, the it will idle at about 2500 RPMS. Normally it idles at about 500 to 800. Has anyone experienced this issue or have any suggestions?

777jfk

I have a nice set of Special Petcocks I bought on ebay thinking they were for a Standard. Look in the Parts for Sale forum, I have pictures.

[79XS11F]

Your high idle may also be a vacuum leak in the intake system.
Petcock screens may be plugged up.
Rob

[DGXSER]

The high idle issue, might be an intermittent vacuum leak. Might look at changing the vac caps on the synch ports.

The "petcock" issue is due to a faulty "Octy" since you have a special. On both models the fuel flow is controlled by a vacuum operated valve to only allow fuel flow when the engine is running. On both models, the prime position of the petcocks bypass this feature. On the standard models, the petcocks are vacuum operated to control fuel flow. On the special models the petcocks are NOT vacuum operated, they added a vacuum operated valve downstream. It sits on top of carb #2 and has four fuel lines, two in from each petcock and two out to each of the carb inlet Ts and it has a vacuum line that connects to the synch port on #2 intake, nickname "The Octy".

That little bugger is why you have no fuel flow in ON or RES. Start by checking your vacuum line to it for leaks or kinks. Honestly, alot of folks just ditch the thing and make sure to turn the petcocks to off when your done riding.

[thewiz]

It's even possible ...

that that little bugger ...

That little bugger is why you have no fuel flow

is not even on there!! You haven't said. When that little bugger is eliminated altogether, as many people do, the run position on the petcock becomes "PRIME". ... ON and RESERVE don't work at all.

[777jfk]

Petcock

You guys have helpful. I have to take my tank off to see if this could be the problem. I'll post if it is it.

777jfk

[thewiz]

If the Octopus has been removed ...

the front outlets on the petcocks should be capped off or otherwise plugged.

[Dragon Tamer]

Wiz,
If you cap the front petcock tubes, then the on and off and reserve positions will work as intended and the prime position won't. This gives you an off position to shut off the gas when not riding and the on position when you are. It also will give you a working reserve. The prime and reserve positions both take gas from the lower tube of the petcock but deliver it to two seperate output tubes.

[thewiz]

You're right Dragon ..

Sold my Special a month ago now on which I had bypassed the Octy. Have apparently forgotten since then which outlet was which

Thx. for setting the record straight, sir.

[777jfk]

Petcock & Okty

The throttle stuck on my "79 Special when I opened it up all the way the other day so I shut the bike down with the kill switch and pulled over. When I went to see if I could get it unstuck, I knocked the cable completely off. This was about 5 miles from home so I put on the choke and limped the bike home. Did any of you know that these bikes will do 30 on choke if you take it through the gears. Anyway, when I got it home and started getting into it, I found that the fuel and vacuum lines were brittle and cracked. Since I was replacing them, I thought it would be a good time to take everyone's advice and remove the okty. I followed all of your directions and capped the front tubes on the petcocks to be able to use "On" instead of "Pri" like I have been since I bought the bike. Capping the front ones did not make the "On" work so I reversed them and capped the back ones. Now my bike works in the "On" position. It also has more power since I got rid of the vacuum leaks and the occasional fast idle issue is gone.

Thanks for all of the advise but remember to cap the back petcock tubes for the "On" position to work.

JFK

[oseaghdha]

............................
.................

Thanks for all of the advise but remember to cap the back petcock tubes for the "On" position to work.

JFK

Or..............put the left petcock on the left side and the right petcock on the right side.

"OFF" is handle towards the front.

[DGXSER]

Yep, I agree. If the petcocks are on correctly then the front outlet is PRIME the rear is RES and ON. The petcocks can be switched as suggested, sound sliek that is what you have.

[777jfk]

Petcocks and fast idle

Mine have the Prime toward the front. What way are they suppose to be?

Jerome

[Rasputin]

My first thought was that possibly the vac lines to the carbs were switched and ya had vac opening the octy at the wrong time so the petcocks were not opening right. Now if ya checked all that stuff I am just reading in anticipation of the answers