I had huge problems with this - first with my V-Tower whip (even when run through a bong), and then with my MFLB. It's extra-frustratiing because you can safely assume the same chemicals are present in combusted smoke... along with 400 pf their bestest, harshest buddies. So it made no sense but vapour hits, one time out of five or so, would really shut my lungs down and even seemed to send them into spasm where drawing a breath deeper than avergae burnt like fire and set off more coughing. So the opposite of what we're aiming for, then.
What put mThankse onto the fact is was my technique at fault was my MFLB. I was hitting that ineptly, and noobs will, and got barely any visible vapour, or even taste. 'Screw this,' I thought... then realised I was completely ripped. I was taken aback. Was it possible 15 years of bong smoking has put an iron, subconscious rule in my head thick, throaty, visible hits = satisfaction? Well, it seemed possible, at the very least. SO I tried not giving a crap about visible vapour, puffing slowly, chasing in LOTS of fresh air after each toke and generally relaxing about the whole 'smoking' side of it. I just trusted the LB to do its job and made sure I got plenty of fresh air in after every toke and I was set. In fact, it gets me higher - probably the same reason joints get you so high, namely all the air mixed in with the smoke promotes absorption.
So many can get huge hits, but for me I could get them, but just kept on paying for it and it got scary a few times - even using Ventolin. In my case, it was because I was chasing huge, concentrated, throaty clouds. Not only is that not necessary, it's detrimental and you get higher from less by taking your time and being kinder to your lungs. So lots of fresh air, take your time and trust the device is doing its job. All you really need to do is breathe back and stop the very instant you feel a tickle. THis is the correct way to hit vape, IMHO.