Onan 4000 surging at idle warmed up only

Not sure if this would be the issue, but have you tried playing with the altitude adjustment? (on mine, the knob for this is partially hidden behind a small hose, but it's there)

-Chris

SJ-Chris wrote:
Not sure if this would be the issue, but have you tried playing with the altitude adjustment? (on mine, the knob for this is partially hidden behind a small hose, but it's there)

-Chris

I sure did, and it had no affect on surging at idle when warmed up.

Easy answer. Your Carb is gummed up. There are 16 VERY SMALL fuel jet holes and if just one is blocked will cause surge at idle. It is normal for a gummed Carb to smooth out under load or even increasing the idle speed. DO NOT INCREASE THE IDLE SPEED. Some do this and think they have fixed the problem. All it does is increase the output voltage. Doug

dougrainer wrote:
Easy answer. Your Carb is gummed up. There are 16 VERY SMALL fuel jet holes and if just one is blocked will cause surge at idle. It is normal for a gummed Carb to smooth out under load or even increasing the idle speed. DO NOT INCREASE THE IDLE SPEED. Some do this and think they have fixed the problem. All it does is increase the output voltage. Doug

I read your post too late. I downloaded the service manual and adjusted the speed one full turn increasing voltage up to 122.5 with no load. I increased the sensitivity adjustment screw but put it back where I started. The surging is gone with or without load. However, while doing the adjustments and testing, I found that the Hz was fine with good load from AC, microwave or electric water heater. But when I have it only with converter charger with a high charging rate the Hz fluctuates between 45 and 62Hz. What's that all about? Happens only when converter charger is the only load on the generator. If I turn on anything else it settle down to 62Hx.

SFVdave wrote:

dougrainer wrote:
Easy answer. Your Carb is gummed up. There are 16 VERY SMALL fuel jet holes and if just one is blocked will cause surge at idle. It is normal for a gummed Carb to smooth out under load or even increasing the idle speed. DO NOT INCREASE THE IDLE SPEED. Some do this and think they have fixed the problem. All it does is increase the output voltage. Doug

I read your post too late. I downloaded the service manual and adjusted the speed one full turn increasing voltage up to 122.5 with no load. I increased the sensitivity adjustment screw but put it back where I started. The surging is gone with or without load. However, while doing the adjustments and testing, I found that the Hz was fine with good load from AC, microwave or electric water heater. But when I have it only with converter charger with a high charging rate the Hz fluctuates between 45 and 62Hz. What's that all about? Happens only when converter charger is the only load on the generator. If I turn on anything else it settle down to 62Hx.

Well, you have opened up a can of worms. Basic rule is, you NEVER have to adjust the governor or mixture screws. What you did is common among people that do not know what they are doing. The Carb holes are gummed up. You remove the needle jet that has those small holes and clean and blow out the debris. 60 htz is the correct frequency. 126 to 132 volts is the no load voltage. Doug

SFVdave wrote:

dougrainer wrote:
Easy answer. Your Carb is gummed up. There are 16 VERY SMALL fuel jet holes and if just one is blocked will cause surge at idle. It is normal for a gummed Carb to smooth out under load or even increasing the idle speed. DO NOT INCREASE THE IDLE SPEED. Some do this and think they have fixed the problem. All it does is increase the output voltage. Doug

I read your post too late. I downloaded the service manual and adjusted the speed one full turn increasing voltage up to 122.5 with no load. I increased the sensitivity adjustment screw but put it back where I started. The surging is gone with or without load. However, while doing the adjustments and testing, I found that the Hz was fine with good load from AC, microwave or electric water heater. But when I have it only with converter charger with a high charging rate the Hz fluctuates between 45 and 62Hz. What's that all about? Happens only when converter charger is the only load on the generator. If I turn on anything else it settle down to 62Hx.

I am setting both back to the original spots and taking it in the the Onan shop next week. Let them sort it out.