Onan 4000 generator cranks but won't start

Like in many Briggs motors, genset has a decompression feature on the cam shaft gear. Failure of this device is common in some briggs.
Engine parts breadown

Update: Generator FIXED...here's what was wrong....

So my local RV mechanic had told me that the engine on the generator was done/broke and that it doesn't make sense to replace the engine on these Onan 4000 generators (...I've actually heard that from a couple of knowledgeable mechanics). My options were to buy a new one or a used one.

While investigating buying new, I learned that it would cost ~$4000 shipped for a new Onan 4000 generator (which I was okay with) BUT it would take somewhere between 10-29 weeks to deliver. There is a big parts/component shortage causing huge delays. I didn't like the idea of waiting. So I started looking for a used Onan 4000 generator. I quickly found out that there weren't really very many options. I found a couple locally, but the owners could never get back to me with answers to my basic questions and they seemed flakey.

Then I feel like I lucked out....I found a guy who is retired and now seems to have a passion for rebuilding/refurbishing RV generators. Sounds like he's done dozens and dozens of them over the last 10 years. Incredibly knowledgeable. He had an Onan 4000 that he just finished refurbishing that I could buy for $1700 that was fully tested and operating to spec (and he could demonstrate happily). He also offered to help install it into my RV with my help. I felt like I struck gold finding this guy and made arrangements to visit him (...he was a couple hundred miles away, but I could turn it into a mini-vacation and visit a friend of mine who happened to live nearby). He also insisted, "Let's take a quick look at your current non-running generator and see if we can fix it...that way you won't need to buy this refurbished one." You can tell a lot about the guy's character right there...he wasn't just trying to sell me his latest refurbished generator.

So I visited him on Monday. He asked me if I wanted to just drop it off, or if I was interested in learning more about these generators and I could troubleshoot it with him. He is a bit of an old-timer and I could see that he probably would enjoy some company. And, Since I'm always looking to learn, I stuck around. After about 2 hours he was able to identify what the problem was and he declared, "I can fix this generator for you!".

Here's what the problem was....(Please excuse me if I mis-name any components in my description...I'm not a mechanic)... Once he removed the carburetor he could see the throttle plate (flap) on the carburetor had broken free and was forced downstream and he thinks it might have been wedged in a way that was holding the valve open (hence no compression). We found the throttle plate lodged in that region. There are 2 screws that hold that plate on and they were missing (...presumably they went through the engine). We pulled the cylinder head/cover to inspect the piston and the chamber and you could see on the piston there were some marks/scuffs, but the chamber looked great with no damage. He said my carb looked beyond repair, but he had replacement/rebuilt carbs. He told me he was highly confident that he could quickly refurbish my generator, replace the carb, replace anything else needed while he was in there, do a valve job, etc. He is the kind of guy who could probably rebuild this generator with his eyes closed, AND he took great pride in his workmanship and wanted to make sure when he was done fixing the generator it would be at factor spec/tested and working as good as new (he had all necessary equipment/tools and then some). I left to visit with my friend, but he spent 10 hours working on it that day and the next and I came back the next afternoon and we tested it and reinstalled it. I helped out as much as I could with various aspects and enjoyed learning in the process. He even did a little welding on my support brackets because there was some rust that made him uncomfortable on the brackets and now they are super reinforced. Once installed, we tested it again and it is purring like a kitten even under full load.

I am confident this generator will last quite a while now. Out the door cost for parts and ~12 hours of labor: $780. I'm quite pleased!

Happy camping all!
Chris

Thanks for the positive results!

FYI....

For anyone in the Seattle area we have a great generator tech named Chuck. He's in Auburn, Wa. He agreed to come out to me (Renton-Highlands) and diagnose my Onan Microquiet 4K which would only run if I hold the start button.

I initially checked with a volt meter some pins and narrowed the issue down to either a bad control board or voltage regulator. When Chuck showed up he threw his Flight Systems G-Man 360 on it and within 5 min bingo...bad voltage regulator.

The voltage regulator that was on it had been replaced back in 7/11 with a Flight Systems 305. I was leaning at it being a bad control board.

So if you need a generator looked at call Chuck (253) 820-1388

Thanks for letting us know the outcome, especially with such a great story and a happy ending.