Honeywell GEn repair or Sell for parts????

Hi folks I am asking this question as I have had this gen (Honeywell HW2000i) for sale. And the last weekend of this season (2 weeks before the new owner was to take it) it died. What happens is it will not get more than above idle and there is no A/C coming from it.. I am going to buy a yamaha or honda but wanted a bit of a seed egg for it...
Where and what can a guy look for to determine the problem..

THanks