You could remove the freewheel and apply some light lube (Triflow) to the back of the freewheel. If needed, whack the freewheel with a small hammer to free the pawls.
That did the trick on a bike I worked on yesterday.
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The Lord is merciful and gracious, slow to anger and abounding in steadfast love. - Psalm 103:8
I am a cyclist. I am not the fastest or the fittest. But I will get to where I'm going with a smile on my face.