head gasket leak?

I have a 87 reliant 2.5, It starts o.k. when cold but after 5 mins. it stalls.I wait 5 mins. and it runs fine. I checked all vaccum lines,changed map sensor,fuel filter the pvc valve and air cleaner also new fuel regulator. Could the head gasket need torqing? Also, will head gasket cause this problem? It's pretty consistant. Any ideas? I would appreciate any comments. Thanks