2007 Cummins Onan 5500 marquis gold gasoline generator

[jimhunter50]

My 2007 Cummins Onan 5500 marquis gold gasoline generator runs for 2 minutes cold then stops once warm and choke opens, it will continue to run if I manually hold the choke closed. I have cleaned the fuel tank, hoses and filters. Put 5 Gallons on new fuel on the tank. Pump seem to work fine. I clean the carb twice with Sea Foam and then had it sonic cleaned by a carb shop. Same issue, no change. Starts cold, runs for about two minute with the choke automatically closed until its warm and when the choke automatically opens the generator stops. I can keep it running by manually holding the choke closed. Code 36 -

[akcooper9]

lincster wrote:
Very interesting akcooper9.
If this works, people are going to be mad at you that they spent so much money over the years. LOL

I wish I could take credit but it was this post that lead me down the path: http://www.rvamerica.com/TownTalk/RVAmericaForums/tabid/79/forumid/1/postid/373218/scope/posts/Default.aspx

Like most, I cleaned and cleaned and clean with no success. It wasnt until I pulled the altitude screw and cleaned that passage did I have success.

My father also has a onan 5500 that was having running issues and once he pulled the altitude screw and cleaned, his generator ran like a champ again.

[lincster]

Very interesting akcooper9.
If this works, people are going to be mad at you that they spent so much money over the years. LOL

[allcool]

akcooper9 wrote:
Pull the altitude black cover off, mark the screw and turn it in and count the turns. Then pull it out and clean the passage. Put it back together and it will run like a champ.

Very interesting...

I'm good with carbs... but I've tried to rebuild/clean/sonic clean/carb clean soak/etc, the onan 5500 carb all to no avail. Many times on many Onan5500 carbs. Its always bothered me that this onan carb I could never rebuild successful, its the only carb out of dozens,(maybe hundreds)I've rebuilt/modified successfully. But never took out the altitude adjuster screw and looked at/cleaned that fuel circuit(dummy). Took off the plastic cap but never thought it through enough to realize that circuit is the main fuel feed to the engine at load. That passage way has to be the main fuel feed in order to be able to compensate for altitude at all loads/rpm.

Guess for me, and probably many of us, most carbs we have worked on don't have the ALT screw adjustment circuit. I knew it was there, but I never thought it through realizing what it actually was/did, till you brought it up now, thanks.

After thinking about this, you might be exactly right and found the problem area that none of us have found till now. As long as you can remove the varnish gum that probably is in there, that might bee the fix. Worth a try. Probably can even do it with carb still on engine since that adjuster is kind of easy to get at. I will try that next time I'm helping out a buddy on their Onan all to common carb problem.

What has been your method of successfully cleaning the altitude compensation screw circuit..?

jmo

[akcooper9]

lincster wrote:
If the carb sat with old gas in it for too long, carb is gummed up.
I have read very few cases of people being able to get their carbs cleaned out of the very small orifices well enough to get the genny to run.
Most have to buy a new carb.

This is due to the altitude screw. One needs to pop the black part off and then unscrew the screw and clean.

[lincster]

If the carb sat with old gas in it for too long, carb is gummed up.
I have read very few cases of people being able to get their carbs cleaned out of the very small orifices well enough to get the genny to run.
Most have to buy a new carb.

[nayther]

If these "simple" fixes don't work then you've got a clogged jet or two, probably the primary jet or a passage in the carb. Unfortunately you've not filled out your profile so we don't know what state you're in. In CA we get some pretty crappy fuel, all in the name of "clean air" and it gums them up and ethanol totally screws up carbs.

[akcooper9]

Pull the altitude black cover off, mark the screw and turn it in and count the turns. Then pull it out and clean the passage. Put it back together and it will run like a champ.

[newman_fulltime]

take the gas cap off the tank see if it runs i had a few where they were not venting properly causing the line to suck shut

[azdryheat]

When you open the choke it increases the air flow but the gas flow is insufficient to maintain a proper fuel mixture; the mixture leans out and the engine quits. My guess is there is a clog somewhere in the fuel line or in the carb. One thing we used to do with cars was to blow out the fuel line to the gas tank with compressed air. Clog could also be caused by clogged jets in the carb.