Onan MicroQuiet 4000 crapped out while running

[Isaac-1]

My first thought it the linkage may be sticking at full throttle, otherwise look up the governor tuning procedure in the service manual.  Generator frequency is directly tied to engine running speed which should be 3600 rpms +/- 150 on this model, ie 3750 rpm at no load, droop to no lower than about 3450 at full load.  Anything much higher will trip the overspeed shutdown.

 

[Henry J Fate]

Yup. Make sure all the linkage is moving freely and I would lightly oil everything. There are 2 adjustments. One is for setting the engine speed and the other is for keeping it at the set speed during varying loads. You may need a frequency meter or you can gradually turn the set speed down until it provides constant power under no load. Use a volt meter as a reference. Voltage will increase with a speed increase and decrease with a speed decrease. The goal is to adjust it so that it runs within voltage and frequency maximun limits under no load and runs  above voltage and frequency minimum limits under full load.

There is a fault code for voltage minimum and maximum as well as the frequency fault code previously identified.

 

[DonTom]

Overfrequency means the engine is spinning too fast.  Most likely cause is something binding the throttle linkage open.  Or it could be internal, dirt keeping the governor from working properly.

Yes, I think something probably broke while running.  Something that controls the engine speed.


Today, I disconnected from this full hookup  RV park to drive this RV to an area that won't bother anybody. I tested the generator after doing some work on it. I notice nothing was fixed, but I also noticed the error codes but I didn't look them up until I got back to the park to see that my generator idle  was too high according to the codes.  I suspect something broke in that linkage above the carb, perhaps from  the vibration while it was running last week at Organ Pipe. Today, I only looked at it. I am thinking perhaps I can manually slow it down so it will run to give me an idea of what probably broke.


I wish I could compare that area of mine to another generator somewhere. Then the problem I have wih my generator  will probably be obvious.


-Don-  Yuma, AZ

 

[DonTom]

Yup. Make sure all the linkage is moving freely and I would lightly oil everything. There are 2 adjustments. One is for setting the engine speed and the other is for keeping it at the set speed during varying loads. You may need a frequency meter or you can gradually turn the set speed down until it provides constant power under no load. Use a volt meter as a reference. Voltage will increase with a speed increase and decrease with a speed decrease. The goal is to adjust it so that it runs within voltage and frequency maximun limits under no load and runs  above voltage and frequency minimum limits under full load.

There is a fault code for voltage minimum and maximum as well as the frequency fault code previously identified.

I do have a frequency meter here, a little model AECM0020, which will also measure the AC voltage. I leave here on Monday and then I will find a place to play around with the generator a bit more. At least I now have an idea of what to look for and how to adjusts. Thanks.


Sounds like the fix could be a simple adjustment, but it probably won't adjust because I think something broke that holds the carb  linkage in place. But I think I will be able to figure it out the next time I work on it.  Doesn't sound all that complicated to slow down an engine a bit!


-Don-  Yuma, AZ

 

[DonTom]

Look at the photos below and let me know if I found my high idle problem. Looks like a shaft broke in the linkage on the right side of the carburetor. I see a hole, threaded, but the bottom of the threads are missing, so it looks like it broke right there. Is it even supposed to easily lift out of the carburetor?


Seems like a strange place to break from normal operation.


-Don-  Yuma, AZ

 

[Lou Schneider]

I don't recognize that piece, but if it's stopping the throttle from returning to a closed position it will certainly cause high idle.  Same for the screw at the base of the throttle shaft that sets the idle speed - if it's too far in it will raise the speed.

Note when the engine is stopped the throttle (the shaft on the right side) is held wide open and unless the engine is hot the choke (on the left) is closed..

 

[DonTom]

I don't recognize that piece, but if it's stopping the throttle from returning to a closed position it will certainly cause high idle.  Same for the screw at the base of the throttle shaft that sets the idle speed - if it's too far in it will raise the speed.

Note when the engine is stopped the throttle (the shaft on the right side) is held wide open and unless the engine is hot the choke (on the left) is closed..

It's the shaft shown on the right side of the first photo, on top of the carb.  It's broken, I think, so whatever it is supposed to change in the carb is stuck there. I have no idea what that will do to the RPM of the engine. I don't even know what it does or if there is a return spring in the carb for it.  But it certainly doesn't look right to me.


I assume it's part of the carb and not part of the linkage. So I probably have to replace the carburetor to fix the thing. Then I can learn about the adjustments. This is the very first time I have done anything to my generator other than change its engine oil, so I should  learn a lot from this experience.


-Don-  Yuma, AZ

 

[Lou Schneider]

Reolacement carburetors are cheap - I picked up a new one on Ebay for $40.  Search based on your model number.  There are several YouTube videos showing how to change them out - there are a couple of tricks due to the tight clearances.

 

[DonTom]

Reolacement carburetors are cheap - I picked up a new one on Ebay for $40.  Search based on your model number.  There are several YouTube videos showing how to change them out - there are a couple of tricks due to the tight clearances.

Yeah, I was just checking, and discovered this.


So, yeah, my broken part is part of the carburetor. That shows a clear picture of what my lingage should look like.



Thanks for the note to check on YouTube Videos. I will order the carb when I get back home from this trip. I probably won't use the RV  again for six months or so, so I have plenty of time for this repair. 


I have been on the road for about two months on this trip.


-Don-  Yuma, AZ

 

[Isaac-1]

As mentioned it is tight clearance getting it in there, I suspect whoever changed it failed to loosen a couple of screws on the divider wall and forced it into place instead cracking that shaft.

p.s. occasionally genuine Onan carburetors show up on ebay for a reasonably price, I picked one up last year for about $75 new in box.  Supposedly the seller had sold the motorhome, and was then selling off spare parts he had found laying around.

If finding a deal fails, you can always buy a refurb from this guy https://www.ebay.com/itm/Onan-OEM-FACTORY-ORIGINAL-CARB-Microlight-4000-KY-RV-Gen/293931034317

 

[Tom55555]

Below will show photos of why I could not figure out the switch on my generator.


The outer piece, which I didn't even know existed, I found in the bottom pan in my generator.


The good news is not only does the switch still work as a two piece switch--it even cranks the generator!


I put the control board back  in for a few seconds just to see if it would crank from that generator switch, and to my surprise, it did!


The switch still will not hold together but it works fine as a two piece switch. I just have to be careful to not lose the piece that I never knew existed.


I should have my fuel pump & filter  on Monday and then perhaps I can get the generator running again.


But I am now  in an RV Park in Yuma, so I will have to test it elsewhere after I put it together. I think I can get away with working on the generator here, as that was how I just removed the switch. This is a dumpy RV Park anyway (Yuma Mesa RV Park). But I will not try to run it while here.


-Don-  Yuma, AZ

Don,

I noticed Yuma and thought about the 3:10 to Yuma movie. Great western in my opinion. Russell Crowe does a good job.

Don't watch this movie trailer if you can't handle violence. https://www.youtube.com/watch?v=gV4WFBjc01I

Good clip from Gladiator: https://www.youtube.com/watch?v=X1UmHfWCw-4

 

[DonTom]

As mentioned it is tight clearance getting it in there, I suspect whoever changed it failed to loosen a couple of screws on the divider wall and forced it into place instead cracking that shaft.

p.s. occasionally genuine Onan carburetors show up on ebay for a reasonably price, I picked one up last year for about $75 new in box.  Supposedly the seller had sold the motorhome, and was then selling off spare parts he had found laying around.

If finding a deal fails, you can always buy a refurb from this guy https://www.ebay.com/itm/Onan-OEM-FACTORY-ORIGINAL-CARB-Microlight-4000-KY-RV-Gen/293931034317

I would expect that the Onan generator carburetor in this RV was never replaced, but I did buy  this  RV around seven or eight years old with just under 100K miles on it. I don't remember  the generator hours, but they were then very low. So I assume this is the carb that came from Onan with the new generator.




Are there any issues with the new $40.00 carbs on Amazon (or E-bay)?


Don-  Yuma, AZ

 

[DonTom]

Don,

I noticed Yuma and thought about the 3:10 to Yuma movie. Great western in my opinion. Russell Crowe does a good job.

Don't watch this movie trailer if you can't handle violence. https://www.youtube.com/watch?v=gV4WFBjc01I

Good clip from Gladiator: https://www.youtube.com/watch?v=X1UmHfWCw-4

No TV cable here. I watch very little TV. Ham radio keeps me busy from my RV, so I do not miss not having TV. But the violence is fine as long as they do not overdo it to the point of being ridiculous.


-Don-  Yuma, AZ

 

[DonTom]

Looking at the top of the  Carburetor here, 5th photo down,  it's quite obvious I found the problem.


-Don-  Yuma,  AZ

 

[Isaac-1]

The quality can vary on those cheap import knock off carburetors, some have been reported to have the wrong size jets, some of been reported to have hard point instead of soft point needles, etc.

 

[DonTom]

The quality can vary on those cheap import knock off carburetors, some have been reported to have the wrong size jets, some of been reported to have hard point instead of soft point needles, etc.

I put in one of those cheap carbs and got the generator working for a while. It ran for 20 minutes or so and I had it what I thought was reasonable, 62 hz no load, 58 hz heavy load and 60 hz with moderate loads. But then the engine died with a code 36 (not from controller--just died) before a half hour. It started again okay, but did the same thing in another 20 minutes or so. It has plenty of gas, so that is not the issue.


And then I started to have trouble restarting. Perhaps I tried too many times to restart, as now I have a starter that won't crank! And the voltage going to it drops below ten volts (tested on solenoid)  when  trying to start and I think I saw some smoke in there!


So either I have a frozen engine (even after I removed spark plug) or a shorted out starter or both!  Looks like I will now have to remove the generator out from the RV to see what happened.


BTW, on the linkage, there is the choke and the throttle control. The one for a throttle has a small spring. Where does the carb end of that spring connect to?  Doesn't seem to be a place for it.




-Don-  Auburn, CA

 

[Isaac-1]

Running for 20 minutes or so then dying is a classic symptom of a fuel pump going bad on these units.  As to the starter, I don't envy you, if it is dead and needing to be replaced.  I had to replace one on my Onan 4000 a couple of years ago, and had to partly drop the generator to get to it (I used a $60 motorcycle jack from Amazon).  At the time the best price I could find on a genuine Onan starter was from PPL in Houston, I think around $75, though generic imports are available for about half that.

 

[DonTom]

Running for 20 minutes or so then dying is a classic symptom of a fuel pump going bad on these units.  As to the starter, I don't envy you, if it is dead and needing to be replaced.  I had to replace one on my Onan 4000 a couple of years ago, and had to partly drop the generator to get to it (I used a $60 motorcycle jack from Amazon).  At the time the best price I could find on a genuine Onan starter was from PPL in Houston, I think around $75, though generic imports are available for about half that.

I now expect my problem of the engine dying was the choke not turning off. The spark plug looks VERY rich.  My fuel pump is new, changed a few weeks ago in Yuma (mentioned several messages back). But I did remove the hose from the carb to watch the gas shoot out when I hit prime at the switch.  New fuel pump is doing it's job.


Perhaps a choke adjustment is necessary for the new carb. Hopefully, it's not a jetting problem from the cheap carb that you tried to warn me about!  But one thing I can say for the cheap carb is that the pin that broke in the Onan OEM carb cannot break in the cheap one. It's a thick shaft where the Onan thin pin broke.



I own several small  flat motorcycle lifts, so I am well covered there. 


I think I want to totally remove the generator to really check things out. I have a lot of questions about how the thing works that I want to see for myself.  Such as the carb linkage. What controls it?  I can't see back there very well but it looks like it's on a shaft that is controlled by whatever.


I don't feel too bad if it's just the starter that crapped out. I realize they crap out fairly often.


-Don-  Auburn, CA

 

[DonTom]

BTW, on the linkage, there is the choke and the throttle control. The one for a throttle has a small spring. Where does the carb end of that spring connect to?  Doesn't seem to be a place for it.

I just found a photo of it above, from my old carb, but it makes no sense. The thin rod goes to the same place as the thick rod--and at BOTH ends!  How can that do anything?


See photo here, the very thin rod on the right. It has a spring to the right but after the spring it is tied to the same rod, so the rod makes sure the spring cannot do anything. And that was before I touched anything at all.


Can any body make sense out of it?


-Don-  Auburn, CA

 

[Isaac-1]

One rod is moved by the thermal automatic choke, the other is moved by the governor to maintain engine speed, the springs are there to act as return tension.

Here is a youtube video showing them in action (though poorly) https://www.youtube.com/watch?v=oJXl7eprUsA