After start it will show a hard draw for a while to recharge the battery. Assuming you know that and you've driven several miles to allow the recharge, it sounds to me like you have a serious current load going on. Something pulling a lot of juice. The ammeter will drop at idle simply because the generator can't put out more at idle. I'm certainly no expert but if it were me I'd put a known good ammeter in the circuit and see what it says. If it shows a 25-30 amp draw when running you have some investigative work to do. Good luck.
Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.
| 
