Similar idea to mine, I use Schwalbe 26x1.0-1.5 in my 2.2 tyres, never had a problem, they are 125g and I only pay £4 (about $6 US) each.
A friend uses 29er tubes in his home built 36er as the 36" tubes are 500g EACH.
So I'd say it's worth trying the 2.1's......
thankyou, i emailed sjs cycles yesterday and they told me........ "The SV14 X light tubes will be fine for use in your 2.4” tyres.
I wouldn’t recommend the 2.10” versions though, the thin rubber cannot cope with the extra volume needed to inflate a 2.4” tyre.
Normal weight 2.10” tubes tend to be fine, but not the extra light versions."
i think thats the crux is that there the extra light versions and best not to push them too much.but then it could just be them covering there asses perhaps