Truss rod doesn't work

I'm trying to adjust the truss rod on my Z-3. It has a bi-cut birdseye maple neck. I want the neck to become just a little bit straighter, it has slightly too much up-bow, but nothing happens. It's like it doesn't work at all. When I loosen the truss rod nut totally, the neck curve stays the same as it is. When tightening it, still no effect at all. Up to the point were it really gets hard to turn the nut, I stop because I don't watt to damage it. With any other necks a quarter turn will do the job.
The guitar plays well, and I can live the the slight up-bow, but it's not normal.
Is there anything I can try?

Ivo, if I understand your post correctly, you have too much upbow. If you have loosened the trussrod nut and it hasn't changed, you neck has developed a backbow and this type of trussrod will not remove this. What I would do is take this to a competent luthier who steams necks and have them remove the bow. I just had one done and it worked great and the cost was very reasonable. If this guitar is still on warranty it should be returned to your dealer for warranty work, However, you say that it is a birdseye neck and they have a short warranty. Bottom line is that I think this is very fixable-- Darwin

Yes, that must be it Darwin.
The saddles are also at their lowest position, which could be related to the same problem.
I was thinking about shimming it, but perhaps it's not necessary after the bow is removed.
I'll take it to the luthier this afternoon, see what he says.
About warranty. I know G&L gives only 3 months warranty on birdseye necks, but this was not the case at the time I bought it. I have a certificate with the guitar saying 10 years warranty. But I'm not going that route, I don't want to send it back to the importer and all the hassle, when I have a very good luthier close by. I'll pay for it myself.
I'll post a follow up when I know more.

Yes, that must be it Darwin.
The saddles are also at their lowest position, which could be related to the same problem.
I was thinking about shimming it, but perhaps it's not necessary after the bow is removed.
I'll take it to the luthier this afternoon, see what he says.
About warranty. I know G&L gives only 3 months warranty on birdseye necks, but this was not the case at the time I bought it. I have a certificate with the guitar saying 10 years warranty. But I'm not going that route, I don't want to send it back to the importer and all the hassle, when I have a very good luthier close by. I'll pay for it myself.
I'll post a follow up when I know more.

so it has a back bow? never heard it referred to as up-bow. darwin is right, the trussrod can not fix that. they put it in a jig and either leave it i a hot car for a few days or steam it.

I was afraid it would be tough to explain the situation in English.
Let's forget about the bow, let me try it this way: When you loosen the truss rod totally, you get too much relief (what I accidentally referred to as an up bow). Tightening the truss rod nut (turning it clockwise) should straight out the neck up to the point where you have the desired relief. This did not happen. I could turn the truss rod nut until it hardly moved, almost got stuck, and still nothing happened. Still too much relief.

I took it to the luthier, and he removed the truss rod nut, lubricated it, added a small steel tube, and put it all back.
Now it works again. I have got the desired relief, and turning the truss rod nut goes easier, but still heavier the my other G&L's. I'm sure nobody knows what the hell I'm talking about, but it's fixed, and for free.

that's the same issue darwin had, i have too, the truss rod runs out of adjustment. the nut is not drilled deep enough, and you have to get a new nut or put a washer underneath, which is what your tech did.

that's the same issue darwin had, i have too, the truss rod runs out of adjustment. the nut is not drilled deep enough, and you have to get a new nut or put a washer underneath, which is what your tech did.

You mean there are not enough threads on the truss rod, right?

I think the issue is that some truss rod nuts are not drilled deep enough. Some of the earlier truss rod nuts were drilled all the way through. If the nut stops and becomes tight it is time to add some washers. -- Darwin