For Vietnam we used:
Trousers: light kevlar lined jeans - combined with hikking rain over-trousers when it rained (no chance in Vietnam to go faster than 40 or 50km/h so hikking rain trousers were adequate and pack very small). I combined them with light riding long johns for comfort.
Jackets: Husband had his Weise jacket which is NOT GoreTex and has lots of vents. I heard no complain and he seems to love it.
I had my very old knackered BMW Santiago jacket (zip had all been replaced, aweful zips!).
Since then, I had to get rid of my jacket (too old and in terrible condition!) and just bought a Held Tamira Jacket for my trip across the stans next year (There is a male version of the Tamira).
It has lots of vents and again, light fabric, so should work in the heat. I have not given it a try yet, but seems very light. I will combine it with a goretex liner. When it gets cold I will just add layers.
Note: any jacket, no matter how light, you will fry in the heat. When I lived in Brazil I used a RevIt summer jacket, with large mesh pannels. It is great but only perfect if you are sure to have only very hot weather.