Cold start trouble

I bought an old 85 VW Polo for my girlfriend to learn to drive in. I've given it an oil change and new sparks, but I have real trouble starting it up from cold. The battery is new, and the starter cranks the engine fine, but I can rarely get it to fire up without connecting jump leads to my car with the engine running to. Once I do this and crank it few seconds it starts. Once started it runs fine. If I stop the engine and start it again its fine for the rest of the day. I got it going last night about 7pm, tried to start it this morning 6am and it just cranks again.

Anybody no what might be up? I've checked the I get a spark from each plug, and all apear fine. Could it still be a fault with the coil not giving a good enough spark. I've checked Petrol is getting to the sparks. It runnigs ok once started, so I'm a bit lost.

it could be a couple of things. The battery is not the right size. The starter is dead.( Remember , a dying starter will "crank" but it won't start the car).Check the timing. the cap may be out.