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Onan late model carburetors with altitude adj.


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  #1  
Old 09-15-2011, 05:54 PM
land land is offline
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Default Onan late model carburetors with altitude adj.

I'm having a problem figuring out how to open carb while still mounted, no room to unmount, would like to clean bowl, blow out internal ports but can't figure out how to take off bowl. Older models have bolt under bowl for simple removal and giving access to fuel level valve and back flushing to supply line.
Down loaded manual for BGM but it only covers previous models.
Model # 5-58GMFA26105H Serial D990895699
Marquis 5500 for RV Gasoline
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Dave
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  #2  
Old 09-15-2011, 07:08 PM
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Billy J Shafer Billy J Shafer is offline
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Default Re: Onan late model carbureters with altitude adj.

Take a good look under the carb. I think you will find the bowl nut. You may have to remove the plastic adjuster to get to it.
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Old 09-15-2011, 07:26 PM
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Default Re: Onan late model carbureters with altitude adj.

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Originally Posted by Billy J Shafer View Post
Take a good look under the carb. I think you will find the bowl nut. You may have to remove the plastic adjuster to get to it.
Plastic adapter is the knob for the altitude adj. How do you remove it? No obvious way. With a price of almost 200 bucks for new carb, don't want to break it.
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Old 09-15-2011, 07:30 PM
Max Thompson Max Thompson is offline
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Default Re: Onan late model carbureters with altitude adj.

http://www.cumminsonan.com/www/pdf/m.../965-0531B.pdf
Try this one, it covers the latter model BGM. Give it some time to download, it is a large file.
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Old 09-15-2011, 07:34 PM
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Billy J Shafer Billy J Shafer is offline
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Default Re: Onan late model carbureters with altitude adj.

It will pry off. Just take it easy.
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Old 09-16-2011, 01:54 PM
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Default Re: Onan late model carbureters with altitude adj.

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Originally Posted by Billy J Shafer View Post
It will pry off. Just take it easy.
Wrong!!
New ones don't pry of they break.
Adj. Lever is attach by a rivet like shaft, which breaks.
The right way to take off the bowl is to unscrew entire bowl until treaded center bolt is loose enough to allow it to come off. Top of bowl is resting on o-ring at top, breaking the shaft at the bottom has a small o-ring sealing the bowl atltitude lever connection. Small O-ring is held in place by using the shaft rivet shoulder to keep it in place.
Now I have to try and find a replacement bowl and adj. knob set, temp fix will try to reengineer the bottom of the nut to hold the small o-ring in place.
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Old 09-16-2011, 02:34 PM
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Billy J Shafer Billy J Shafer is offline
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Default Re: Onan late model carbureters with altitude adj.

Sorry about that. But you must have a carb I have never seen. Because I just rebuilt one two months ago.
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Old 09-16-2011, 05:33 PM
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Default Re: Onan late model carbureters with altitude adj.

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Originally Posted by Billy J Shafer View Post
Sorry about that. But you must have a carb I have never seen. Because I just rebuilt one two months ago.
Did it have the altitude adj at the bottom where the usual bolt to remove the bowl is?
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Old 09-16-2011, 07:12 PM
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Billy J Shafer Billy J Shafer is offline
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Default Re: Onan late model carbureters with altitude adj.

Yes they are all at the bottom side facing out. Sorry for your mishap. But anyone on this site will tell you. I do not give out bad advice. At least I try not to. Been with Onan since 1980.
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Old 09-16-2011, 08:08 PM
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Default Re: Onan late model carbureters with altitude adj.

Quote:
Originally Posted by Billy J Shafer View Post
It will pry off. Just take it easy.
You did say take it easy, so I did but I should have taken it easier
yesterday I broke the second limb trimmer from HF, nice to know my strength at 71 is still strong, but I have a feeling chinese pot metal is the problem.
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Old 09-16-2011, 11:44 PM
pegasuspinto pegasuspinto is offline
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Default Re: Onan late model carbureters with altitude adj.

I'll second that you can pry off the plastic, this works fine on even the later model carbed' sets made in the late 2000's. Their idea of altitude adjust might of been fine when new but 15 years later, some wear and tear, ethanol fuel later you gotta get more range of adjustment at times. After all the altitude adjustment is REALLY the 'full load mixture' adjustment of old. One thing we can't convey on the internet is the 'touch and feel' of experience, that is why we can get them off without breaking things-anymore. LOL.
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Old 09-17-2011, 08:26 AM
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Default Re: Onan late model carbureters with altitude adj.

Well pinto I still break things at times. Broke a headlamp on a fork lift the other day. Still don't know how I did it. Some days it pays to stay in bed.
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Old 11-23-2013, 07:41 AM
Mike Muetzel Mike Muetzel is offline
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Default Re: Onan late model carbureters with altitude adj.

Altitude adjuster is the topic that got me on this thread. But my genset is a microlite 2800, tag letter "G". We have owned it last 3 yrs, it's always run a bit lean and been hard to start here at sea level. I finally tried popping the anti-tamper disc off the idle mixture screw and with 1/8 turn ccw fixed that. But it also acts like too lean under load. The anti-tamper for the alt adjust looks like a solid brass plug. Can it be pried out? Dremel'd out? I'd like to borrow a pound of experience, please.
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Old 11-23-2013, 08:13 AM
Gunny Gunny is offline
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Default Re: Onan late model carburetors with altitude adj.

Suggest starting a new thread and posting the COMPLETE Model/Spec/Serial number.
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Old 11-23-2013, 09:26 AM
Jim Rankin Jim Rankin is offline
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Default Re: Onan late model carburetors with altitude adj.

Pictures are a good idea too. Yours may be different than the one I have in mind.
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Old 11-23-2013, 12:00 PM
Kpack Kpack is offline
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Default Re: Onan late model carburetors with altitude adj.

Read this on another site and I believe it. I'm ready to try it on a couple of 4000 microlites for friends that are having problems.
(I have a 5500 onan in my new fuzion and it's always had a lean pop out the exhaust and would surge when not under a load. I am a diesel tech and refused to buy into the fact these carbs can't be cleaned and made to run good again.
I always ran seafoam and ran the generator under load once a month. I finally gave up on the seafoam and removed the carb for cleaning. Once I got the carb off I took it to work and took the carb completely apart. No signs of dirt or varnish and jets where clean. We have a ultrasonic carb cleaning so I dropped the carb into it and let it do it's thing. Once done I washed out the carb and blew it out with air. Next I took some gasket paper and made 2 new gaskets to replace one on top of carb and one that goes between carb and intake. Took the carb back home and installed it back on the generator along with 2 new spark plugs. The gen fired right up but the lean pop was still there and surge was a little better. I knew this carb was clean because it ran good but just had this small lean pop.
Well I wasnt going to give up so I called the small engine mechanic at work and told him what was going on. He told me to bring him the carb because he knows what's wrong with it. I removed the carb again and took to work the next day. I gave him the carb and he said give me a few minutes to fix it. 20 minutes goes by and he walks up to me and says your done. I ask him what was the problem. He brings to tell me he sees it all the time with these new generators and small engines. He says they are running these engines so lean because of emissions standards today. He shows me a set of real tiny drills to drill out main jets. He found the stock main jet size to be .0250 and just opened it up to the next jet size of .0280. One size wasn't a big jump but he says trust me that's all it needs.
So I take the carb home and installed it back onto the generator. Prime the carb and say to myself well here goes nothing. The motor fired right up and.....WOW! This generator has never ran this good from day one. This thing sounds totally different. I start to think this thing sounds quieter also. Next thing I know my wife walks up and says man it sounds quieter. lol I also installed a shut off valve in the fuel like so I can run the generator out of fuel. )
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Old 11-24-2013, 03:47 PM
Mike Muetzel Mike Muetzel is offline
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Default Re: Onan late model carburetors with altitude adj.

Quote:
Originally Posted by Gunny View Post
Suggest starting a new thread and posting the COMPLETE Model/Spec/Serial number.
i'll try this thread first, if no response, will take that advice, thanks, Gunny.

model number 2.8KVFA11574G - serial number J973753789

i don't know where the spec number is on the sticker.

i'm an aircraft A&P mechanic, have worked on Marvel, zenith, SU, and bing carbs before, understand a LITTLE bit about carbs in general. did i emphasize LITTLE enough? i have a copy of the Onan RV Genset service manual 11-04 981-0518E. it's a bit sketchy on the later model carbs. my carb is the type illustrated in FIGURE 8-17. CARBURETOR ADJUSTMENTS (BEGIN SPEC E, MODEL KV; ALL MODEL KVC) on page 8-15.

this genset acts like it's running too lean at rated rpm under load. i figured before dismantling the carb and drilling main jet (which is irreversible) it made sense to just rich the main adjustment screw a bit and see what happens. i'm guessing (GUESSING) that the main adjustment screw shown for the older style carbs in FIGURE 8-19. CARBURETOR OVERHAUL (PRIOR TO SPEC E, MODEL KV ONLY) is what is hiding behind the brass dot in the center of the plastic cap on my altitude adjuster. but i don't like basing potentially expensive work on guesses.

please, anyone have practical experience on IF the main mixture adjustment screw is what the late-model carb "altitude adjust knob" is, and IF there is a good, non-damaging way to get at it and adjust it? i don't care if i destroy the plastic cap, as long as the main mixture adjustment screw still works properly.

related question. if screw adjustment doesn't work and enlarging jet is required, we ARE after the part labeled "main nozzle" in figure 8-19, right? i'm GUESSING it's the same part and place in the figure 8-17 type carbs. practical experience, please?

i've tried attaching photos, but y'all have the sticker numbers and the service manual figures to work with in case they don't jump on. thanks!
Attached Thumbnails
onan info sticker.jpg   onan 2800 carb.jpg  
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Old 11-24-2013, 03:58 PM
pegasuspinto pegasuspinto is offline
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Default Re: Onan late model carburetors with altitude adj.

that is the main mixture adjustment, the plastic knob. it should at least be set to 'zero' altitude, full rich. I've never had to drill out the jet, just knock the plastic off and give it another 1/4 turn open or so. there is also a possibility there is dirt in the jet as well, which is under the needle.
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Old 11-24-2013, 04:26 PM
len k len k is offline
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Default Re: Onan late model carburetors with altitude adj.

First thing I do is clean outside of carb with toothbrush, gasoline and compresser air so sand doesn't stuck on mating surfaces..... it always does. Then I remove carb and fully disassemble inside of carb and clean everything. I have similar gen (7NHM) but I think yours is the newer EPA type carb (they don't want you taking it apart). I don't have experience with bowl on those. On mine didn't have all that junk on bottom of bowl. I just pulled plastic altitude knob off, then it's like any other lawn mower carb. Just use wrench to unscrew the aduster "bolt" and bowel comes off . Mine did not have a rivot. I haven't seen that type, maybe drill out the rivot???

When I bought mine it would hardly run. Cleaned the Niki?? carb and it ran perfect. With ethanol gas , it make tan desposits inside that plug up tiny jet holes, even seen a Generac with large jet hole completely plugged.

Once you have bowl off there are 2 jets to unscrew and clean in the carb bowel diptube. Each gas jet tube has 6-8 tiny holes that easily plug up with this junky ethanol gasoline. One is easy to see, other is hiding behind a screw cap. I clean everything with gasoline and toothbrush, then blow it out with compresses air (I have 150psi tank) Including the passageways that lead to M+S air jets at top, and the tiny .010" holes in the carb throat.
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Old 11-24-2013, 10:07 PM
len k len k is offline
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Default Re: Onan late model carburetors with altitude adj.

............

Last edited by len k; 11-24-2013 at 10:52 PM. Reason: deleated info, you don't have a BGM......Confusing, that's why we like to have thread be just one gen
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