Maiden Voyage was great until...fuel leak from air box

[mmatches1]

I took the bike out for the first ride since a carb overhaul and it operated very well and I had a great ride. I pushed it into the garage and about 1.5 hours later I noticed that gas was leaking out of the air box. I had left the petcoks open and closed them and the leak stopped. I had the bike running several times at idle for approx 1 hour total with no sign of a leak or gas in the air box.

The only difference is that I swapped out the fuel tank yesterday - took off the 1979E tank and added the original 81 tank. Both fuel lines have the petcock filters and inline filters.

During the rebuild I measured the float levels and all checked out with spec. The only new part I added during the rebuild was the needle valve float seat o-rings.

It seems to me that one of the floats was fine but is now sticking. I am wondering if I should replace the needle valves and perhaps the float seats?

Any ideas? I read another thread and someone flushed gas through the bowls to flush material that may have plugged the floats.

[jetmechmarty]

I'm not sure what you mean when you say you left the petcocks on. Do you have a Special or a standard with aftermarket petcocks? If your bike is a standard with stock vacuum petcocks, one or both of them has/have failed and is leaking. If you have a Special, the vacuum shutoff failed and you need to fix it, or if you removed it, you need to learn to habitually turn the petcocks off.

Did you replace the float bowl gaskets? Maybe a float is hanging on that. If you remove the bottom of the airbox, you can determine which carburetor has failed. You may have just picked up trash in the needle seat, or a needle is hanging up. The needle could even be cocked and hanging open. Having gone through this, getting the problem corrected can be frustrating. I've got to where I can remove the carburetors in 10 minutes or less. I got plenty of practice going through this.

So, you have one or more petcocks to rebuild, and one or more carburetors to fix. It's possible that the carb can be fixed without parts and it sounds like you know what you're doing.

Here's some help with the fuel valves:
Rebuilding Yamaha Vacuum Operated Fuel Valves (Petcocks.)

[GLoweVA]

The standard tanks should have the vacuum control petcocks, so without the engine running, the petcocks should have sealed/stopped flow.
I think that's your first problem. (there's a small spring in there that seats the petcock when there's no vacuum, or the seat is worn too thus allowing leakby) (If the 79's petcocks held good, then you can swap the petcocks into the 81 tank)

If you've got the 81 carbs, then you should have the side bowl drains.
I'd suggest checking your fuel heights with tubing hooked to the bowl drains to see what the actual level is vice the measurement of the float.
If one of the seats isn't seating properly then fuel will continue to flow and you'll see it in the tubing. (at least then you'll know which one to attack)
Here's the tech tip thread: http://www.xs11.com/forum/showthread.php?t=76

Maybe one of the floats is hanging up on the gasket?
Some like to do the blow test to see if the valve seat is leaking by.
Invert the carbs (this makes the floats go shut) and blow into the fuel inlet.
If air is moving thru, then that seat isn't seating.

Hope this helps.

[jjz28]

if it was coming out the airbox, it might be in the oil too. I would definitely check your oil.

[mmatches1]

The petcocks are the vacuum type and I rebuilt the petcocks with a kit and thought I assembled them properly. However, thinking I knew what I was doing I didn't follow the rebuild procedure on the site. Next time I will know better. Also, I now know that the some of he aftermarket rebuild kits do not fit properly (purchased a terrible KZ400 kit). I will dismantle them and try again.

Kind of good in a way that the carbs leaked because now I know that the petcocks were not properly assembled. Strange thing is that they didn't look that complicated. My petcocks are from the 81 and I transferred them to the painted 81 tank. Are the 79 vacuum petcocks different from the 81? They look very similar.

I find it odd that the carbs worked fine for a couple of weeks and then failed after a good ride. I seem to remember that I left the petcocks in the on position with the other tank and they did not leak. The only change was the tank. I did replace the float bowl gaskets with another set of paper types during the rebuild. I remember Rasuptan saying that he didn't like the paper ones. I did replace the o-rings in the valve seats so that shouldn't be an issue.

I will pull the carbs and have a look. It is much easier to do now after doing it many times. Just a pain when I want to be out riding instead. I probably should have replaced the needles during the rebuild. I will also check the float level with the tube. The same procedure is recommended for my KZ and I haven't tried it yet. Thanks for the help!

Do I know what I am doing? Probably not. I started working on bikes approx 2 years ago and the learning curve is steep. I fix something, get cocky, get in over my head and foul things up. Fortunately, this site has bailed me out many times and I have learned allot.

[jetmechmarty]

The XS1100F and XS1100H share identical petcocks. I had success rebuilding these things with the K&L kit. It's not too difficult to do the job right and have success. Most of us just need a little guidance. Without taking all the proper steps, and throwing a kit at these valves, the result is usually failure.

Here's a link to a kit:

2x YAMAHA XS1100 PETCOCK KITS

[motoman]

May also wanna pull the carb bank, remove the bowls and with a razor blade leaving gasket in place, trim anything protuding to inside of bowl. Doesn't take much to interfer with floats, plus tightening the bowls will allow any excess gasket material to protrude even farther. replace the viton float needles at same time if you haven't already. Replacing those may require float adjustment correction too.

[DGXSER]

ok, first off, lets not blame the petcocks because your float valves are not hol ding. You should be able to leave the petcocks in PRIME and not leak a drop of fuel. Since you rebuilt the carbs, it certainly would have been a better idea to replace the float valves and seats at that time. But, you may just have a float that is hung up. You can tap on the side of the offending float bowl with a screwdriver handle and it will often times correct a non-seating float.

You also may have gunk in the 81 tank that was not in the 79 tank and got down into the carbs. Causing a float valve to not seal properly.

As to the petcocks, I do recall several folks finding the vacuum valve in the kits being just a hair to short and not sealing properly. Of course, you can create an off position on the standard petcocks, there is a thread on here somewhere with how to do that.

[mmatches1]

And the winner is - paper bowl gasket rubbing on the float. I trimmed it up and everything is back to normal. Nasty quality control on these gaskets.

[motoman]

And the winner is - paper bowl gasket rubbing on the float. I trimmed it up and everything is back to normal. Nasty quality control on these gaskets.

Good to see you found the issue...............and posted the findings!

[CaptonZap]

Good to see you found the issue...............and posted the findings!

Amen to that! We all learn from the solutions to the problems, and when guys don't post their fixes, we're all left wondering.
Thanks for letting us know.

CZ

[mmatches1]

I dismantled the petcocks and will give a second rebuild a go tomorrow. If the pistons are too small as suggested on this thread I may be out of luck. I didn't find any issues when taking it apart. Are petcock problems related to a poor seal on the thin rubber gaskets? Any other common issues I should look for?

[jetmechmarty]

It's all here:
Rebuilding Yamaha Vacuum Operated Fuel Valves

[mmatches1]

The vacuum fitting on the right petcock was plugged. I cleared it with carb cleaner and hope it does the trick. Thanks!