Onan 4000 hard starting, oscillating RPMs

[RPCcompass]

The new Cummins Onan 4000 generator (5 hrs) on my Compass B+ is hard to start. When running the RPM oscillates, particularly at light loads. I have pulled the fuel line to the carburetor and seem to be getting good flow. Have not tried cleaning the carb or a new full filter. Suggestions? Is there a good troubleshooting guide.......Cummins tech support have been quick, but their suggestions have not helped.

 

[widdershins]

with 5 hours, should still be under warranty?

 

[TheLooks]

What he said^^^ Surging is a function of carburation. Either the governor is way out of adjustment or the carb is plugged in the Idle circuit. This causes it to die on idle, governor opens throttle allowing increased air flow pulling gas in from the main jet. Then it dies and does it again.

 

[RPCcompass]

What he said^^^ Surging is a function of carburation. Either the governor is way out of adjustment or the carb is plugged in the Idle circuit. This causes it to die on idle, governor opens throttle allowing increased air flow pulling gas in from the main jet. Then it dies and does it again.

I will try a carb cleaner. The units at unused for about 5 months. It ran fine for an hour about a week ago.....when I started it up day before yesterday is when it started oscillating.

 

[TheLooks]

They should be run every couple of weeks. DO NOT use ethanol gasoline in an engine that will set. Most carb cleaners will not touch the stuff that forms with ethanol. I have had some success with Seafoam and Marvel Mystery Oil......your mileage may vary. Techron is a carbon cutter but not what is plugging the carb. So many generators are failing with similar problems that I suspect dirt or debris from installing them is at play. But many of them set to long. Tod Henson of NRVTAA did a tech tip Tue. on Youtube last week about this.

 

[RPCcompass]

They should be run every couple of weeks. DO NOT use ethanol gasoline in an engine that will set. Most carb cleaners will not touch the stuff that forms with ethanol. I have had some success with Seafoam and Marvel Mystery Oil......your mileage may vary. Techron is a carbon cutter but not what is plugging the carb. So many generators are failing with similar problems that I suspect dirt or debris from installing them is at play. But many of them set to long. Tod Henson of NRVTAA did a tech tip Tue. on Youtube last week about this.

I don't use ethanol on any of my small engines, but the Onan draws from my RV gas tank. I had to have my home generator carb redone several years ago because of ethanol. Thanks for the advice, May end up taking it into the shop.

 

[Scooterfan]

I'm sure you are aware that "built in" RV generators that pull from the gas tank have "limiters" that will shut down the unit if your gas tank is low. Mine will do it when slightly below half full. Make sure you keep your tank full and eliminate that as a possibility. Some generators will oscillate a bit with no load. Make sure that when you get it started you give it something to do Run the coffee maker or hair dryer ! Good luck

 

[TheLooks]

Good advice Scooter. Make it work a little bit.

 

[RPCcompass]

I'm sure you are aware that "built in" RV generators that pull from the gas tank have "limiters" that will shut down the unit if your gas tank is low. Mine will do it when slightly below half full. Make sure you keep your tank full and eliminate that as a possibility. Some generators will oscillate a bit with no load. Make sure that when you get it started you give it something to do Run the coffee maker or hair dryer ! Good luck

Vehicle tank is almost full....good supply going to the carburetor. Oscillation reduces when I load with AC, but still oscillates. Other day it shutdown on it's own. Couple of weeks ago it ran well for an hour. While running i can see the linkage responding.

I'm sure you are aware that "built in" RV generators that pull from the gas tank have "limiters" that will shut down the unit if your gas tank is low. Mine will do it when slightly below half full. Make sure you keep your tank full and eliminate that as a possibility. Some generators will oscillate a bit with no load. Make sure that when you get it started you give it something to do Run the coffee maker or hair dryer ! Good luck

 

[Scooterfan]

Have you tried adjusting the carburetor ? I'm certain you have tried it all Is your's the "micro quiet" ?

 

[RPCcompass]

Have you tried adjusting the carburetor ? I'm certain you have tried it all Is your's the "micro quiet" ?

Thanks for the recommendation....I have started to search for instructions on how to adjust the carb. My manual is no help. Series R generator, but I don't think it is the Microquiet

 

[Scooterfan]

On an older one (Onan 4000) I simply played with the adjustment screw on the carburetor and it solved my problem. Try and locate it and move it each way in small turns and see if it helps.

Perhaps the screw with the spring

 

[RPCcompass]

On an older one (Onan 4000) I simply played with the adjustment screw on the carburetor and it solved my problem. Try and locate it and move it each way in small turns and see if it helps.

Perhaps the screw with the spring

Thanks I will give hat a try

 

[RPCcompass]

Thanks I will give hat a try

Ran 4 ozs of SeaFoam in non-ethanol gas and think I fixed it. I only run non-ethanol in my small gas engines.....had to have my house gen carb rebuilt to teach me that. I hope I have fixed it.

 

[Little Bitty Zitty]

Word of advice, start your generator once a month and let it run about five minuets, that will keep carburetor clean and fresh fuel in it. Learned that on my old RV which I bought used. Owner hardly ever ran generator, so I ended up removing carb and cleaning it.

Word of advice from an ASE certified Master Mechanic since 1974.

 

[RPCcompass]

Thanks....lesson learned....for the second time. I had to have my 2009 portable generator carb rebuilt because of ethanol. "Assumed a 2021 generator would not have the same issue. Wrong.....ended up having to replace carb and fuel pump.