Seems perfectly possible you're going to remain stuck. I don't see you registering a Himalayan in Oklahoma (or elsewhere in the States), since the bike is not sold here. That's not about emissions; it's about a whole raft of safety, emissions and bureaucratic issues. It sounds like you've already determined that you can't sell it in Britain or the EU. And you'll have more immediate problems trying to enter China than an absence of carnet--particularly if you're subject to budgetary constraints.

You're also experiencing the fact that the carnet system is well-designed to do exactly what it's supposed to do, which is to extract a severe penalty should you not return the bike to where you bought it. Most of that huge deposit would be refunded to you, but only once you've returned the bike.

On a positive note, American tourists are more welcome in Iran than previously--at the moment, only with official guides AFAIK. Maybe things will relax by the time you're done contemplating. Give it a couple of years. As an alternative, maybe ship the Himalayan elsewhere--like East Africa. Have your adventure. There are workarounds for almost everything, including carnets, if you're determined. The key is not to get too attached to a specific outcome, like " finally to sell in EU."

Hope that's helpful.

Mark