How do you stop generator from stalling under load

Clean out the carbretter , add new fuel

As you have not provided me with the information I requested I'm going to have to take a few guesses here Bob. You could be overloading the generator. You can't run a 10,000 BTU air conditioner off of a 1000 watt generator. You need to look at your load, (what you are trying to power), and determine how much power it needs. Almost everything has a tag somewhere on the device. Most don't give watt requirements. But they do tell you, how many amps the device pulls, as well as the voltage the device needs. So you need to do some math here. Volts X Amps = Watts. So if we have a 120 volt device, that pulls 15 amps, we need 1800 watts to power it. But it gets a little more tricky than that. Motors are often rated at what they pull while they are running! But it can take two or three times more power to get them started. Example... A motor rated at 10 amps, using 120 volts will be 120 X 10 = 1200 watts. But it could take 2400-3600 watts to get it running. So in theory a 3000 watt generator may die before it can start that load. Heating elements are also power hungry! Let's say you have a small 800 watt generator, and your just trying to run a simple coffee pot! Well the heating element in a typical coffee pot pulls 1000-1500 watts. A hair dryer or microwave oven rated at 1000 watts, is the power they produce, not the power they consume! So a 1000 watt microwave may pull 1600 watts of power to run. Most non US generators are highly over rated as well. I certainly would not trust a Harbor Freight 3000 watt generator to actually put out 3000 watts of power. Not that they are bad units, I would expect their numbers to be under PERFECT conditions. Temperature, humidity and altitude also play a part! Your 3000 watt generator is going to put out more power at 50 degrees, at sea level, than it is at 7000 ft in the mountains at 100 degrees. So my "guess" Bob, is that your just asking more from the generator than it can produce. Picking out a generator is not as easy as it looks. "Hey that one is $1000 and this one is $300! They both make power! What's the difference". The difference is what do you need to run! "Heck I'll just get that 50,000 watt unit"! Yeah you can do that too, but you will never use that much power, and you will burn way more fuel than you need to. My other "guess" is that you have a governor issue on the engine. As load increases the gov will throw more throttle to the motor. My generator has an option to run full speed or on the gov. So it will idle and burn less fuel while I am hammering in a nail, then go to full power when I trigger a saw connected to it. Lot's of factors involved here Bob.