Can anyone suggest what I'm doing wrong?
Have previously used Mavic UST rims & UST tyres no problems.
The tyre is seated and I can inflate it no problem but there is air escaping around the base of the valvle stem.
I was thinking...
1) More sealant & sloshing around
and/or
2) Reseat valves with a small square of old inner tube around stem.
could be the tape creased up creating a small gap. i did 2 runs of tape around mine and just a small x with a scapel to push the valve through.
How do you maintain continuous tension in the tape while applying it?
I use a small round file to neatly remove the tape around the valve hole after finding that they leaked if the tape wasn't tidily removed. Done 5 sets of ZTR rims now and none have leaked since doing this.
How do you maintain continuous tension in the tape while applying it?
Either get a mate to help or apply the tape with the wheel in the bike and the bike upside down and a foot to operate the brake lever.
I have the same, on a brand new set of stans wheels no less...found the tape was torn after much complaining/faff...will have to fit some fresh tape
There's a video on youtube on how to apply the tape
Cheers folks. A few things to try there.
Found this occurring when I tried tubeless for the first time about a month ago with my 355 rims. I assumed I just hadn't done the screw up tight enough on the valve so that the rubber bit on the valve hadn't got pulled into the valve hole sufficiently...screwed it up nice and tight and didn't have a problem after this and they haven't lost air since.
You could use a small gasket/bit of inner tube over the valve on the inside and outside of the rim. The newer valves have a different shape rubber bit which seems to help.
I think the tape went on OK (no creases) but I didn't file off the tape in the valve hole after poking a small hole through it (using a Stanley knife).
Thanks to everyone for the suggestions.
A combination of filing the yellow tape around the valve hole, an improvised rubber gasket around the valve stem and tightening up the valve washer had fixed the leak.
Bodge-tastic!
Stick to Mavic in future, much more professional
I used to use rim strips but as I had 355 rims recently I went for valves - the new std valves seated very well - I did not tape around the hole but used a Stanley to create a clean cut - not issues here?
I did not tape around the hole but used a Stanley to create a clean cut - not issues here?
I did 'Stanley' a small cross cut but initially left the flaps(?) of tape on. I guess air was escaping from between these bits and the rubber base of the valve stem. OK, my solution was perhaps a bit overkill, but it has worked. Well, I say worked, the tyres were still fully inflated this morning (10 hours later)....hopefully they still will be when I get home from work.
Stick to Mavic in future, much more professional
Yes, I agree that Mavic's UST rims are generally less faff to set up. However, this was part of my DIY blingy wheelbuild...White Flow rims on 2nd hand gold CK hubs. Only the 2nd set of wheels I've built. Going to batter them on tomorrow's ride to test the build. Gulp.
I await flaming for having tarty wheels.
Bodge-tastic!
In my experience if you actually bother to follow the instructions it all works without issue:
In my experience if you actually bother to follow the instructions it all works without issue:
Where's the fun in that? 
As above, it's probably a small spit in the tape from assembling the valve.
I just did my first set without paying attention, made a single slit with a knife, pushed the valve through and the slit extended past the valve and never sealed properly.
I re-taped the rim, made a round hole (or, a star of slits works just as well if that makes sense) pushed the valve through without ripping the tape further to do so and now I find it works every time.
God luck with your 2nd set of tape!
P.S. don't forget to tighten the valve in good and snug 
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