tendency

So not sure what's going on here. First time using Continental tubes and, this is the 3rd one I've run, every time I need to fill the tire I have to unscrew the core all the way out and release all the air in the tube to get the tip able to accept air. If I just unscrew the tip to the end of the stem I can't get air in. Never had this issue with non-removable core tubes.

Iride01 

You have to release all the air? There have been times when I have to simply depress the valve briefly to free it up when stuck.

Did this start when you also changed pumps? I might can see that a big bore pump might make you have to push harder on the pump handle than you think you should to get the valve in the stem to open.

But I don't know that I've ever had presta's with removable cores. So if they behave differently, I'd not know.

shelbyfv

This does sound like a pump issue. In practice, tubes with removable valve cores function no differently than others. Unscrew the nut, burp the valve, pump it.

tendency

That's what I thought too however when I unscrew the valve I can't burp it as you say. I've fiddled with several of these conti tubes and have had the same issue with each. Unscrew the valve and unable to burp - that's the prob. only after I unscrew the core and re-insert I'm able to burp. Havent had this issue on non removable core tubes. Dunno

shelbyfv

Maybe you are unscrewing the entire core instead of just the little captive nut? Be sure the removable core is tightly screwed into the valve.

Crankycrank

+1. And it's also good to check the removable core in a new tube for tightness. Some are not quite as tight as they should be.

JohnDThompson 

If you can't "burp" the valve, perhaps replace the core with a different one. Valve cores can be purchased separately or salvaged from discarded tubes. It's particularly handy to have an extra core or more available if you use sealant in your tubes. The sealant eventually clogs the valve; when that happens, remove the clogged core and soak it in household ammonia solution to dissolve the sealant. Put a fresh core in the tube while the old one soaks. Rinse out the old core after it has soaked, and put it in rotation for the next time this happens.

daverup 

I've had a couple of those do the same thing recently. I don't really understand why, but have not tried cleaning the core yet.

squirtdad

Are you using sealant? I had core get mucked up with sealant.....I just treat them as an expendable and replace

55tele

I’ve had a similar issue…I tried replacing the valve and didn’t improve…..it’s got to be something in the stem…..when it first happened I needed to replace the tire, so I pulled the valve out…

In my case, the pressure from the pump opens it ok…it’s going the other way / relieving pressure “manually” that’s the problem…

i think Continental in China made a bad batch with something clogging the stem…

tendency

I agree 55tele - gotta be a bad batch as I don't use sealant and I'm quite certain that I am only unscrewing the nipple on the stem and not the entire valve.

Thanks all for the feedback since other's have had this issue I'll chalk it up to bad quality control on the manufacturers part. Back to my Michelin's

Iride01 

Just be sure you are pushing down on the pump handle with enough force. My son normally rides at a what to me is a low tire pressure. He decided to try a higher tire pressure and couldn't figure out why he couldn't get to 110 PSI with the same pump I routinely get to 125 PSI and higher.

He just needed to push harder as the tire filled up. He'd never experienced that much push back from the pumps piston before and thought something was wrong.

But sure, it might well be a bad batch of valves.