Chain rings/front mech problem

[Night Train]

I have picked up a bike for a friend and checked it all out and it seems fine. It is just a cheap steel MTB style, non suspension, road bike.

The problem I have found is that when changing from the middle chain ring to the big chain ring the chain drops down between the two rings. Changing from big to middle is ok and I can change from middle to small and back and from small 'thrown' all the way to big and back.

It seems odd that the chain is dropping down the gap between the middle and big rings.
What's wrong?

Edit to add: The bike was from freecycle so no taking it back.

Thank you.

 

[mickle]

It's an old chainset (5/6/7) with a modern narrow (8/9) chain?

 

[Steve Austin]

Try adjusting the top screw, so it can be pushed further over ie onto the big ring

 

[Night Train]

It's an old chainset (5/6/7) with a modern narrow (8/9) chain?

How do I check and what is the best solution?
I think the bike may have been new like this as nothing has been worked on at all.
The front cranks are a one piece with a peg driving the chain rings.

Steve, if I shift quickly then it will go onto the big ring fine, it is only if the shift is slow or hesitant that it drops between the two.

 

[Night Train]

I've just had a proper look and it seems that the gap between the big and middle rings is anout 1.5 times the gap between the middle and small rings.
I think it might just be down to 'cheap rubbish'.