Really using Clen and an ECA stack together will just result in quicker receptor shut down. I'd advise to use one or the other. I'd use Clen, over ECA, and combine it with yohimbine hydrochloride which will inhibit the receptor shutdown. This means that instead of only getting results for three weeks, you may get five to six weeks.
Clen needs to be cycled up slowly then tapered off. Starting dose would be around 40mcg up to a max dose of 120mcg. Take 30mg of yohimbine HCl ED. When you finish the Clen cycle leave the same length of rest period before starting another cycle (e.g if your cycle was 5 weeks, give yourself 5 weeks rest). This will hopefully stop your body from adapting to the Clen.
I hope this has helped.