“I’ll try” is usually a polite way of packing an escape route. Say yes or say no.

Hedged answers protect you from the discomfort of refusing while leaving the other person with nothing they can plan around. They also protect you from yourself, because a soft commitment can be dropped without ever having been broken. The kindness is only apparent, and what you are actually doing is moving the uncertainty onto someone else.

When you mean no, say no early and without a paragraph of reasons. When you mean yes, say it plainly and then treat it as fixed. If you genuinely do not know, name the date you will know by.