Really really dumb question: Vacuum tube pulling off petcock during rides

[Rust_to_Redemption]

I replace all of the vacuum tubing on my carb when I rebuilt it last year. Since I’ve started riding this season I keep having a problem with the vacuum tube falling off the petcock, eventually killing the bike unexpectedly. I’ve tried zip ties and a hose clamp that is admittedly probably too large to work well. What gives, is there a way to route the vacuum line incorrectly or maybe a way to get back pressure built up where it blows off the vacuum line? I was under the impression that it should just stay put as a friction fit item. I’m using 3.5mm vacuum line that seems to fit tightly, when I put it on it takes a little effort to push on. I’m at a loss honestly, if it hadn’t happened two rides in a row I’d just chalk it up to coincidence, but it seems too weird to not be caused by something.

[chuck hahn]

Maybe a smaller ID line or a drop of super glue. And a smaller wire style clamp.

[Gorminrider]

on all my petcocks the plate with the nipple that is against the vacuum diaphragm is removeable ( 4 screws ) and you can turn it to an upright position. This might help...
there is room under the tank to do this on any of my bikes. Hopefully yours too... Be careful not to lose the spring and so on ...but anyways you should be able to just hold it together and rotate the plate without letting anybits go astray .

But per chuck's is a good idea too as well...you can make a little "clamp" by wrapping copper wire at the union or a bit of spring-steel (guitar string)on a mould that is slightly smaller than the hose...a big nail or spike maybe...

[Rust_to_Redemption]

I was under the impression 3.5mm was the stock line size. I’ll try a little drop of super glue until I can get a properly sized wire style hose clamp.

[Rust_to_Redemption]

on all my petcocks the plate with the nipple that is against the vacuum diaphragm is removeable ( 4 screws ) and you can turn it to an upright position. This might help...
there is room under the tank to do this on any of my bikes. Hopefully yours too... Be careful not to lose the spring and so on ...but anyways you should be able to just hold it together and rotate the plate without letting anybits go astray .

But per chuck's is a good idea too as well...you can make a little "clamp" by wrapping copper wire at the union or a bit of spring-steel (guitar string)on a mould that is slightly smaller than the hose...a big nail or spike maybe...

Interesting, I will have to check and see if I can flip it up, that might help keep it on there.

[Steve]

For some reason, 3.5mm just seems too SMALL in my mind.

I am under the impression that it's more like 4.5 or 5mm, but I am having trouble finding it on the parts fiche.

Does your bike ever backfire? If it does, and it's #2 that happens to backfire, that might be what is blowing the hose off the petcock.

.

[Rust_to_Redemption]

T

For some reason, 3.5mm just seems too SMALL in my mind.

I am under the impression that it's more like 4.5 or 5mm, but I am having trouble finding it on the parts fiche.

Does your bike ever backfire? If it does, and it's #2 that happens to backfire, that might be what is blowing the hose off the petcock.

.

No backfires, the bike is running perfectly. Maybe I am mis-remembering the size or was told the incorrect size when I bought it. I took the old hose to a local motorcycle shop and they cut me what I needed off their bulk tubing.

[Gorminrider]

You've discovered a new "petcock annoyance" anyways..Never heard this one before and none of mine have ever fallen off... BUT there's at least one of mine that is "original tubing" and a little too easy to put on and off from removing the tank. The end of the tubing gets permanently enlarged a bit.

Otherwise just as a thought, if you start the bike on prime, with your finger over the end of the vacuum tube..it's enlightening. You can fell the tube "pulsing" rather than just sucking so if there is back pressure I can imagine how it could blow off especially on a larger cc piston than I have here...