In the long term, you should either switch to FIFO, or turn off negative inventory.  Negative Inventory together with Average Cost does not (and cannot) work well.  

If you post even minor adjustments to sales invoices (i.e. to add a customer PO number, or correct a date) that cause inventory to 'go negative' and back, invoice COGS and inventory value may be changed, even though no transaction took place.

It's possible to adjust either value, or cost, or both at one time in order to correct your inventory balance.

Examples:

 - showing -10 quantity and $-1,000 value.   You know there are 4 on the shelf, and the cost should be $100 each.   Adjust qty up by 14, at $100 each, total $$ adjustment $1400.  This should debit inventory $1400, and credit the adjustment account.

 - Showing -10 quantity and $-10,000 value.   You know there are 4 on the shelf, and the cost should be $100 each.   Adjust qty up by 14, at $1040 each, total $$ adjustment $10,400.

 - Showing -10 quantity and $-10,000 value.   You know there are none on the shelf, and 10 that were sold haven't been invoiced by the supplier, and the cost should be $100 each.   Do not adjust quantity, total $$ adjustment $9,000.  The result should be -10 on hand, total value -$1,000.00

Trying to keep the inventory balances correct, while using Weighted Average Cost and allowing negative inventory is a not-fun game of whack-a-mole.

I hope that helps, please post back.

Thanks for your reply, my issue however is the fact that i have 80 of one item showing in inventory with a value of 4800 but on the income statement it shows as -4800 for that particular inventory item

If the inventory module of the company database is still in 'historical entry', meaning it will let you change the starting inventory balance, then this won't apply:

To correct an imbalance between the G/L account and the total for inventory of a particular account::

http://sagecity.na.sage.com/support_communities/sage_50_accounting_ca/b/sage_50_ca_supporthub_blog/archive/2013/09/18/inventory-gl-account-does-not-match-the-inventory-sub-ledger.aspx

If changes are made to any of the linked inventory accounts and transactions are made later, or if the historical 'beginning balance' is changed, then it's will create an imbalance between the G/L and the inventory ledger / list.  Changing the account link does not change past transactions, so it's also possible to have the accounts in, and out of balance at different report dates. 

Unless you have a strong business need to keep separate inventory accounts, just use one.   Or, never change the linking, just put ZZZ in front of that item and create another one with the correct linking.  

In short, don't change the asset account linking of an inventory item.