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Fixed my carburetor on Onan generator Tom 7-23-17  
I just wanted to share a success I had at getting my Onan generator to run again. The trouble started after the generator sat for about a month without being run, after a short trip during which it worked fine.

For reference, my generator is an Onan Microlite 4000.

As I said, it sat for about a month, and I tried starting it just to keep it in running shape, and it would not start. I tried the usual tests: I had spark, fuel flowed from the fuel line when cranked. Also checked the little solenoid shut off on the bottom of the float bowl to make sure it worked. I figured carb was the problem. I removed the carb, and tried to get a rebuild kit. Rebuild kits turn out to be unavailable. Everything said carburetor must be replaced, at a cost of about $350, although recently I've found sites selling carbs for about $275. Anyway, that cost was way more than I wanted to spend on this old generator. So I partially disassembled the carburetor and cleaned with spray carb cleaner, repeatedly. Note that the main carburetor body has very large passages that can be checked with a piece of wire and none of these were clogged. The flow bowl, however, has some small, pretty much inaccessible passages that I really couldn't check. So I just sprayed lots of carb cleaner in all the little holes.

After all this cleaning, I reinstalled the carburetor. Oh, and since parts for the carb are unavailable, I cut out my own gaskets from material I got at the auto parts store for the carb-to-manifold and carb-to-air cleaner housing mating surfaces. Here's a tip: it's really hard to squeeze the carb in between the manifold and the air cleaner housing; to get a little space, put the cover back on the housing (without the air cleaner element installed) and tighten up the thumb screw; this will squish the rubber gasket in the housing enough to create a bigger gap between the air cleaner housing and the manifold, making it much easier to get the carb in without tearing up the gaskets you just spent an hour cutting out.

Then the generator would start, but would not run normally. Every time the rpm started to pick up, the engine would start to die and rpm would drop. Then it would go through this cycle over and over. I could keep the engine running by spraying carb cleaner directly into the carb throat.

I figured something was still plugged, and I actually went through this whole take carb off, clean it, test it about 3 times. I wasn't going to spring for a new carb, so I started looking at portable generators that I could use instead. Before I bought one, though, I decided to try one more thing, as a desperation move. I've read on the internet about people cleaning carburetors with PineSol. Since I was at the point of calling the generator dead, I figured I had nothing to lose. So carb off once more, and remove float bowl. As noted above, I was pretty sure none of the passages in the main body of the carb were plugged. So I disassembled the parts from the float bowl, except for the altitude adjuster knob which I left attached to the bowl. The float bowl and the brass fitting that screws into the bottom of the bowl separately went into a 50/50 mixture of PineSol and water. I did not put the solenoid assembly that screws into the brass fitting into the PineSol. I left the bowl and the fitting in the solution overnight. Next day I thoroughly rinsed both parts with spray carb cleaner and blew out with compressed air. Reassembled the carb and installed it, and now the moment of truth.

The generator started after maybe 10 or 15 seconds of cranking. It settled into a nice even, normal rpm after just a couple of seconds. I ran it for 45 minutes or so, and it continued to run just fine. Nothing on the float bowl seems to have suffered any ill effects from the PineSol soaking. The labels are intact and the altitude adjustment feels like it turns with same resistance as before. So I consider the PineSol treatment a success.

I'm not recommending the PineSol treatment as a standard technique, but if you're about to call your generator a total loss like I was, it's worth a try.
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