genset bogs down under load

So I replaced the spark plugs & its still doing the same thing. Runs great then when I put it under a light load (both a/c units fan only) that's the only breakers I had flipped. Ran good about 5 minutes then starts to bog down. Then it bogs down every time the air tries to comw on. I go inside & turn off the air & come out & flip the gen breakers off & she runs fine. Turned the breakers back on & go inside & this time turn the a/c on cool to start compressor & it ran good & blew cool for about 4 minutes then it boggs down again & everything shuts off.
I have not put the new fuel pump on yet. Is there anything else to check before I throw the new pump on it?