Finally - Onan code 36 solved!
My problem started shortly after I purchased my RV in July 2006. It would quit when the AC and microwave were run at the same time. Two years ago I tried to use it and it would start, run a few seconds and then die. I could keep it running by manipulating the choke and throttle and spraying carb cleaner into the intake. Same thing last year...
This year, I was determined to get it running. The first thing I tried was Seafoam. I drained the fuel tank, and added about a gallon of gas with the recommended amount of Seafoam, and started/restarted/restarted until I was sure there was Seafoam in the carbuerator and let it sit for a day or two.
When I came back and re-attempted on a couple of occasions- same thing. It would fire immediately, then die.
I went to the local Onan dealer and inquired if I cut the crimped hose clamp feeding the carb would it void my warrantee. They assured me it would not as long as I used genuine Onan parts for anything I replaced (not the hose clamp though).
So, I pulled the fuel line from the carb inlet and ran a hose directly to a 1 gallon can of gas with seafoam and went thru the same exercise with the same result.
Then, I pulled the bowl from the carb and saw that the float was stuck in the up position! I was confident that I found the problem, and sprayed out the bowl with carb cleaner and sprayed around the float and carb inlet, then put it back together. The bowl is easy to remove once the plastic guard below it is removed by removing the two torqx fasteners that attach it to the start swith. With this gone, it is relatively easy to get a 3/4" open end on the solenoid. The bowl screw came off with the solenoid, but it is also accessbile using an 11/16" open end.
At this point, I started to wonder if the fuel pump was good, so I pulled the fuel line and ran it on prime for a few seconds. Gas poured out of the fuel line with a pretty good flow, but when I put my thumb over it, it stopped easily and never built up any pressure that I could feel... But since the pump flowed well I had my doubts.
The next step was to remove the carb and clean it thoroughly. It wasn't that dirty, but I made sure that I got carb cleaner (in a spray can) through all the small passages. I cleaned the bowl, but left the altitude adjustment alone, because the ONAN rep advised me that playing with this would not help. Upon re-assembly, I couldn't even get it to start!
At this point I am wondering if I had goofed up the re-assembly or If I had a problem with spark. I sprayed a little starter fluid in and it fired right up and died. Luckily I had taken a picture of it with my iphone and I noticed that I had the choke positioned wrong - the choke tab needs to point toward the back of the camper. Even with this fixed, it still would not stay running.
I have been working on this every night for an hour or two, followed by google searches on this problem. I learned that the wires going into the bottom of the carb are for the fuel shutoff solenoid. I pulled this back off again and tested it by applying 12V and confirmed that the solenoid retracted the fuel cutoff when energized. Then I verified that the solenoid was being powered by the control board by measuring the voltage out at around 11V when cranking.
At this point I am ready to pull my few remaining hairs out and I spent the 10 bucks to download the service manual from a pdf server. I learned from this manual that the altitude adjustment is actually the main fuel metering jet. If you pry off the plastic cover, there is a thumbscrew jet underneath.
I pulled the bowl for about the 9th time and removed the main jet and the screw below it, which is just a bowl drain. I made note that it turned about 1 3/4 turns into the stop, so I could put it back in the same spot. I cleaned the jet and the passageway with carb cleaner and re-assembled the jet in its original position and the bowl to the carb.
With this fix, the ONAN started and stayed running. After it was warmed up, I still had to turn the main jet in about 1/2 turn to get it to run smoother. At this point it barely even noticed the AC and the microwave were turned on at the same time. It is now running better than it ever has!
In hindsight, if/when this happens again, the first thing I am going to try is to remove the bowl drain screw and shoot carb cleaner up thru this passage and into the main jet area. I suspect this might have fixed my problem in the beginning, since I am convinced that this was the location of the obstruction.
One last word of advice - there are washer/seals at the bottom of the bowl, between the bowl and the bowl screw, and between the solenoid and the bowl screw. Keep track of these because you can't buy replacements!
The ONAN carb is extremely simple, and there are no internal gaskets to tear or dry up. The only gaskets are on the inlet and outlet of the carb. There might be one on the carb at the bowl, but I didn't have any problem with it.
This is a long post, but hopefully this will help someone that is going thru the same issue with Code 36.