I have Spark, but wirks funny. When I connect direct to remote with OTG ewerything looks good, but when via wifi then is video delay halv second and not good signal. Whats the problem?

no problem, just natural delay using wifi vs cable.  weaker/slower/older phones tend to show more delay with wifi transcoding vs brand new flagship phones.  so half a second+ sounds about right when add natural delay + a slightly slower phone.

Please ensure that you fly in a place without interference. Please try to fly in another environment for further check.