Intermittent Internet Access on Azure VM's

Hi 

I have a number of VM's all on a Virtual Network with a DNS server specified which is a VM running AD and DNS - set up as per the Azure documentation

All of the VM's on this virtual network suffer from poor internet access. i.e I can get to google and bing ok but no other sites. This occurs 95% of the time. Then I can go to any site but only for approx 5% of all attempts.

I can't see anything being setup incorrectly or no internet access would work.

Am I msssing something here, what should I look at to troubleshoot internet access on an Azure VM?

Thanks

Tom Hickling