"therefore" after "because" or "since"?

[dihen]

Is this correct or not?

"Since/Because.... , I was therefore not able to..."

[Tdol]

I'd change the punctuation:
Because I was, therefore, not able...

[dihen]

I meant that if a sentence like "Because/Since the weather was bad, I was therefore not able to go" is correct or not?

[Tdol]

'Therefore' is redundant in your example- 'because' gives the reason, so it serves no function. It normally has a suprasentencial reference, hence the commas.