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Old 12-18-2014, 04:50 PM   #1
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1977 31' Sovereign
1996 30' Land Yacht
Riverview , Florida
Join Date: Aug 2006
Posts: 10
Onan 5000 carb issues

I'm working on a 96 30' land yacht that has been sitting for quite a while. The gen hasn't been running in over two years. New batteries and it turns over fine. Checked the plug and it is dry as a bone after cranking. I have gas getting through the filter but I don't see or smell any at the carb. I put a little gas in the spark hole before reinstalling the plug and it seemed to try to start for a short time so I think spark is fine. My guess is that the carb is gummed up and needs cleaning/replacement. I can see the outboard carb attach nut, but can't see the inboard. Is it possible to remove the carb in the vehicle? Alternatively, how do you remove the float bowl to try to clean the bottom jet with the carb installed? Finally, if the unit has to be removed from the vehicle where are the attaching bolts for the unit? I can see two on the outside top on each end of the unit, but nothing inboard. There are a lot of wires running along the inboard top of the unit and they may be hiding something but I don't want to tear them out unless I know it will give me access. Any and all help is greatly appreciated.
Pete
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Old 12-19-2014, 07:25 AM   #2
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1992 36' Land Yacht
Grayson , Georgia
Join Date: Nov 2011
Posts: 772
Give me some more information and I can supply you with the service manual. I need to know the exact model number and serial number of the unit.

Here is a link to the service manual for my genset: Onan Marquis NHM Service Manual



As for removing the carb, on my Onan Marquis 7KW NHM generator, I had to drop the generator to do a complete service of the unit. It sat for close to 7 years and needed a complete carb rebuild, new plugs and have the slip rings cleaned. I don't think it could have been done without dropping the unit. Once down it's a much easier job to work on it. There are several linkages to the carbs that connect the choke and the governor that would be VERY difficult to get to and install properly with the generator still installed on my unit.

On my unit the generator is held in by 8 screws. There were 4 on each side (left and right)along the bottom of the generator. The screws go between the sheet metal panels of the MH and the bottom frame of the generator. There are no screws on the front or back and no screws along the top. On my model the entire generator is housed by sheet metal panels that can not be removed until you drop the unit. I used a motorcycle jack I picked up at Harbor Freight to lower it. If you need to pull it out completely then you may need to raise the MH up quite a bit. I parked mine on a dirt area and dug down below the area of the generator enough to be able to slide the unit out. You may be able to use the leveling jacks to get that side of the MH high enough.

All of this depends on your specific model of generator.
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Old 12-19-2014, 08:06 AM   #3
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1977 31' Sovereign
1996 30' Land Yacht
Riverview , Florida
Join Date: Aug 2006
Posts: 10
Thanks for the help. The model is 5BGMFA26105F and the SN is 1953423134.
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Old 12-19-2014, 09:08 AM   #4
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1977 31' Sovereign
1996 30' Land Yacht
Riverview , Florida
Join Date: Aug 2006
Posts: 10
Also found the mounting bolts. Lots of dirt and grease covering them. I assumed that the whole box had to be removed from the coach and thought the base was welded not bolted together. You are right about having to get the coach up pretty high. I'll have to solve that issue first.
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Old 12-19-2014, 09:38 AM   #5
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1992 36' Land Yacht
Grayson , Georgia
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OK so your generator is an Onan Marquis 5500 watt BGM Spec F generator. The manual I posted a link to should work for your model. You have the electronic governor which makes things a little easier.

You may not need to pull the generator all the way out. Many things can be accessed by simply dropping it to the ground and working over the top. You can assess that once you drop it to the ground. I'd make sure I did have some provisions to be able to lift it high enough to pull it all the way out just in case.

Getting it down is not usually too difficult. Putting it back in does require a little work. The biggest issue I've had with putting them back in is getting the unit and the side screws to line up. Usually if you can get a couple screws in (one on each side) the rest go easier. I've used two floor jacks to jockey it around to get everything lined up. Don't tighten the screws down until you have all of them started. After that it's piece of cake.

The only things that need to be disconnected in order to drop it is the 120V wires, the battery cable and the fuel line. It should just drop down after that. You should disconnect the - battery cable before starting and make sure you don't have shore power plugged in.

While it's out I'd clean the slip rings, replace the plugs, fuel filter and maybe replace the brushes. Depending on the hours and condition you may want to consider replacing the fuel pump. There is a Carter fuel pump that's an exact replacement for the OEM Onan pump. The Onan pump sells for around $230 while the Carter pump sells for around $75. Carter made the pump for Onan. It's a 12V 6psi max pump that is identical to the OEM pump. Part number is P4070.

To clean the slip rings I use a 3M green pad and turn the engine over a few seconds while pressing the green pad down onto the slip rings. You can easily access the slip rings by removing the brushes.

These things are pretty durable and will give you years of reliable service.

Good luck and keep us posted on your progress.
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Old 03-07-2015, 12:17 PM   #6
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1994 33' Land Yacht
bloomington , Illinois
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My 94 airstream has the onan 7000. My carb was gummed up to . I Simply Unscrewed THE Bolt At THE Bottom Of the float bowl . Took bowl off and disassembled the jet in the bowl . It should be an adjustable jet . Simply clean everything with gum out and reinstall . Try not to tear the floatbowl gasket . Because they will want to sell you a whole new carb . Like I said the jet is adjustable depending on if your in the mountains or at sea level . You should be able to adjust your fuel flow
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Old 03-08-2015, 06:34 AM   #7
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1977 31' Sovereign
1996 30' Land Yacht
Riverview , Florida
Join Date: Aug 2006
Posts: 10
Sorry I haven't posted an update. I dropped the generator to get access and found it wasn't as big a job as I thought. Removed the old carb and had purchased a replacement just in case. After I opened the old carb it was instantly obvious that it was beyond cleaning and repair. Entire inside was corroded, gummed up and full of gummed up fuel. Would have been impossible to fully clean everything to any specs. Put the new carb in with new plugs and reinstalled the unit after a good cleaning. Now runs great. I also added a fuel shut off valve right after the new filter so I can run the unit dry after use as someone else suggested. I'm very pleased with the result. Thanks all for the help and suggestions.
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