Home » Public Forums » GMCnet » Onan carb frosting
| Onan carb frosting [message #323952] |
Sun, 17 September 2017 12:32  |
Bierman
Messages: 46
Registered: May 2017
Location: SW Florida
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During the aftermath of Irma my 6k generator started backfiring like shotgun blasts, mind you this was at 3 am , want to talk about waking up the neighborhood. The carb had ice crystals around it and on top ???
Needless to say no ac, sleeping while sweating sucks.
Any thoughts out there,
Thanks
Member, GMCI, Sunshine Statesman and Dixielanders
26' 1978 Eleganza II, new(rebuilt by Sirum) 403, Lenzi hubs and knuckles, front end by Ferrara
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| Re: Onan carb frosting [message #323979 is a reply to message #323952] |
Mon, 18 September 2017 11:10  |
Bierman
Messages: 46
Registered: May 2017
Location: SW Florida
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Replaced air filter, adjusted main fuel out 1 1/2 turns, idle adjustment out 1 turn... Any other adjustments a novice can make?
Member, GMCI, Sunshine Statesman and Dixielanders
26' 1978 Eleganza II, new(rebuilt by Sirum) 403, Lenzi hubs and knuckles, front end by Ferrara
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| Re: Onan carb frosting [message #323981 is a reply to message #323952] |
Mon, 18 September 2017 12:13 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Bierman wrote on Sun, 17 September 2017 13:32During the aftermath of Irma my 6k generator started backfiring like shotgun blasts, mind you this was at 3 am , want to talk about waking up the neighborhood. The carb had ice crystals around it and on top ???
Needless to say no ac, sleeping while sweating sucks.
Any thoughts out there,
Thanks
Bierman,
Icing on the outside of a carburetor is no issue.
If the adjustments you mentioned are as out from a gentle stop, those are just starting points. The 1-1/2 open is like the 8-18-28 rule. (set base timing at 8btdc, points 0.018 and plugs at 0.028 just about anything will run) Once you get there, feel free to adjust to a better place.
Without being there, I would not even hazard a guess as to whether it is rich or lean. Either may cause exhaust blasts like the those noted. Both are the result of a misfire causing a cylinder's worth of charge to be pumped into the exhaust system where the exhaust flame of the next.
If you can load the machine, try leaner first.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Onan carb frosting [message #323992 is a reply to message #323985] |
Mon, 18 September 2017 16:36 |
johnd01
Messages: 354
Registered: July 2017
Location: Sacrameot
Karma: -1
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My coach came whit power level II, I did not know it was not standard
equipment.
My coach seems to hold level well but if I park in travel mode overnight
the left side sages about 2 inches a day. Where should I look for the
problem? Is it worth chasing or should I just be careful to switch to hold?
Is there problem driving in hold?
On Mon, Sep 18, 2017 at 12:10 PM, Randy Cohen/Catherine McGinley <
info@hdforge.com> wrote:
> Ice on the carb is normally something that happens in cold weather, the
> normal fix is to route warm air into the engine. Try some sort of pipe
> pulling air heated by the exhaust into the engine. Last time I had this
> issue was in my 72 Opel GT. I rotated the intake line from cold air thru
> the
> grille to warm air that had passed thru the radiator. End of problem.
> Hope this works, with everything else you are going thru AC at night
> should not be an issue.
>
> _______________________________________________
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*John Phillips*
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Johnd01
John Phillips
Avion A2600 TZE064V101164
Rancho Cordova, CA (Sacramento)
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| Re: [GMCnet] Onan carb frosting [message #323998 is a reply to message #323992] |
Mon, 18 September 2017 17:58 |
Richard Denney
Messages: 920
Registered: April 2010
Karma: 9
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There are many places where a coach will leak down, even overnight. I've
completely rebuilt mine, and it still leaks down.
In Travel, you are depending on not only the control valves, but also the
leveling valves not to leak (plus all their connections). Put it in Hold
and see if it stays up.
And read this:
http://www.gmceast.com/technical/Denney_Power_Level_System.pdf
Rick "whose coach stays up in hold, but not forever" Denney
On Mon, Sep 18, 2017 at 5:36 PM, John Phillips
wrote:
> My coach came whit power level II, I did not know it was not standard
> equipment.
> My coach seems to hold level well but if I park in travel mode overnight
> the left side sages about 2 inches a day. Where should I look for the
> problem? Is it worth chasing or should I just be careful to switch to hold?
> Is there problem driving in hold?
>
> On Mon, Sep 18, 2017 at 12:10 PM, Randy Cohen/Catherine McGinley info@hdforge.com> wrote:
>
>> Ice on the carb is normally something that happens in cold weather, the
>> normal fix is to route warm air into the engine. Try some sort of pipe
>> pulling air heated by the exhaust into the engine. Last time I had this
>> issue was in my 72 Opel GT. I rotated the intake line from cold air thru
>> the
>> grille to warm air that had passed thru the radiator. End of problem.
>> Hope this works, with everything else you are going thru AC at night
>> should not be an issue.
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
>
>
> --
>
> *John Phillips*
> _______________________________________________
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--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com
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| Re: Onan carb frosting [message #324002 is a reply to message #323952] |
Mon, 18 September 2017 19:46 |
McCohens
Messages: 22
Registered: March 2016
Location: Chalfont, PA
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Its not the ambient temperature in your case. I am not sure of the exact physics, but the air flow in the carb and the atomisation of the gas is absorbing heat, the humidity in the air condenses and freezes from the cold. If it happens every few hours, shut the generator down for a while and let the carb warm back up.
Google carburetor icing, wiki has a pretty good explanation. Still hard to believe it could happen at 90, but they say it is also related to humidity.
[Updated on: Mon, 18 September 2017 19:50] Report message to a moderator |
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| Re: Onan carb frosting [message #324015 is a reply to message #323952] |
Tue, 19 September 2017 07:50 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Icing is common enough in carbureted airplane engine to require a means of heating the inlet air as a requirement for certification. As air flows through the carb venturi, it expands, and expanding a gas (lowering its pressure) cools it.It can easily cool below the freezing point and in conditions of high humidity can actually shut the engine down. I've had an airplane engine ice up when it was ~~ 70 degrees outside.
I believe there is a means for letting the intake air on the Onan be drawn from the heated engine cooling air, either by moving the hose going to the filter box or turning a lever, depending on the model. At any rate, do go adjusting thisg if the unit works normally when it isn't icing up.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: Onan carb frosting [message #324016 is a reply to message #323952] |
Tue, 19 September 2017 07:51 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Uh, DON'T go adjusting...
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Onan carb frosting [message #324021 is a reply to message #324015] |
Tue, 19 September 2017 10:16 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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Onan did supply a cold weather kit for the Onan generators. I don’t believe that it is still available, but there is an album on the GMC Photo site called “Winterizing the Onan Generator” that shows you how it can be done. Adjusting your carb will not fix the issue, you can’t change mother nature.
http://www.gmcmhphotos.com/photos/g3021-winterizing-the-onan-generator.html
JR Wright
GMC Great Laker MHC
GMC Eastern States Charter Member
GMCGL Tech Editor
GMCMI
78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan
> On Sep 19, 2017, at 8:50 AM, Johnny Bridges via Gmclist wrote:
>
> Icing is common enough in carbureted airplane engine to require a means of heating the inlet air as a requirement for certification. As air flows
> through the carb venturi, it expands, and expanding a gas (lowering its pressure) cools it.It can easily cool below the freezing point and in
> conditions of high humidity can actually shut the engine down. I've had an airplane engine ice up when it was ~~ 70 degrees outside.
> I believe there is a means for letting the intake air on the Onan be drawn from the heated engine cooling air, either by moving the hose going to the
> filter box or turning a lever, depending on the model. At any rate, do go adjusting thisg if the unit works normally when it isn't icing up.
>
> --johnny
> --
> 76 26' Eleganza(?) with beaucoup mods and add - ons.
> Braselton, Ga.
> "I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
>
>
> _______________________________________________
> GMCnet mailing list
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> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] Onan carb frosting [message #324023 is a reply to message #324021] |
Tue, 19 September 2017 10:44 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Carb ice is a product of humidity and temperature and pressure
differential. Fuel mixture only plays a minor role. When the engine is
under a moderate load, air flow through the carb is high and throttle plate
in nearly completely open. Pressure drop through the carb venturi is at
it's near maximum. That is an ideal state for ice to form if humidity is
high.
I used to have a hot rod engine in my VW Double Cab pickup. Those
weber carbs were mounted high on a steel intake manifold. They would
frequently ice up here in Oregon during the wet cool season. Finally cured
it by throwing away the steel intake manifold and single port heads.
Replaced them with dual port heads, with sodium filled exhaust valves from
Porsche, and EMPI cast aluminum intake manifolds that were exhaust heated.
That one was a runner, with 88 mm cylinders and Malhle high compression
pistons. Had to watch the oil temp on that one. It would get so hot, the
dip stick would burn your hand. Fixed that with a monster oil radiator with
a big fan. Those were the days.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Sep 19, 2017 8:16 AM, "John Wright" wrote:
> Onan did supply a cold weather kit for the Onan generators. I don’t
> believe that it is still available, but there is an album on the GMC Photo
> site called “Winterizing the Onan Generator” that shows you how it can be
> done. Adjusting your carb will not fix the issue, you can’t change mother
> nature.
>
> http://www.gmcmhphotos.com/photos/g3021-winterizing-the-
> onan-generator.html
>
> JR Wright
> GMC Great Laker MHC
> GMC Eastern States Charter Member
> GMCGL Tech Editor
> GMCMI
> 78 GMC Buskirk 30’ Stretch
> 1975 GMC Avion (Under Reconstruction)
> Michigan
>
>> On Sep 19, 2017, at 8:50 AM, Johnny Bridges via Gmclist gmclist@list.gmcnet.org> wrote:
>>
>> Icing is common enough in carbureted airplane engine to require a means
> of heating the inlet air as a requirement for certification. As air flows
>> through the carb venturi, it expands, and expanding a gas (lowering its
> pressure) cools it.It can easily cool below the freezing point and in
>> conditions of high humidity can actually shut the engine down. I've had
> an airplane engine ice up when it was ~~ 70 degrees outside.
>> I believe there is a means for letting the intake air on the Onan be
> drawn from the heated engine cooling air, either by moving the hose going
> to the
>> filter box or turning a lever, depending on the model. At any rate, do
> go adjusting thisg if the unit works normally when it isn't icing up.
>>
>> --johnny
>> --
>> 76 26' Eleganza(?) with beaucoup mods and add - ons.
>> Braselton, Ga.
>> "I forgive them all, save those who hurt the dogs. They must answer to
> me in hell" - ol Andy, paraphrased
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: Onan carb frosting [message #324034 is a reply to message #323952] |
Tue, 19 September 2017 14:52 |
Bierman
Messages: 46
Registered: May 2017
Location: SW Florida
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Thanks for the info guys... But I went and bought a portable generator, I will have to take the gmc out to Sirum in Okeechobbee, I needed ac, been hot in SW Florida with no electric.
Member, GMCI, Sunshine Statesman and Dixielanders
26' 1978 Eleganza II, new(rebuilt by Sirum) 403, Lenzi hubs and knuckles, front end by Ferrara
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| Re: Onan carb frosting [message #324152 is a reply to message #323952] |
Thu, 21 September 2017 18:55 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Carb ice is common on airplanes, (I have experienced is several times), Onans and vehicles with the hot air valve on the intake modified / removed. There was a hot air deflector available for Onans that experience this problem .
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan carb frosting [message #324197 is a reply to message #324166] |
Fri, 22 September 2017 11:10 |
Kosier
Messages: 834
Registered: February 2008
Karma: 1
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Senior Member |
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Larry,
If the ball in the discriminator valve is stuck and allowing liquid fuel to
reach the charcoal canister, it should then drain out through
the filter in the bottom and drip on the ground. Have you changed that
filter lately? They're supposed to be a service item.
Gary Kosier
77PB w/500Cad
Newark, Ohio
--------------------------------------------------
From: "Larry"
Sent: Thursday, September 21, 2017 11:24 PM
To:
Subject: Re: [GMCnet] Onan carb frosting
> I have a new FiTech FI on my Cad 500...now don't stop reading this just
> yet. Hear me out here. Engine started running in the mid to high 11's
> Fuel/Air (FA) ratio. Computer tried its best to correct but could not so
> the engine ran really rich. So I waited until the next day to look at it.
> Started the motor and thinking that maybe I was running to much Fuel
> pressure I left the engine run and went looking for my FP gauge. When I
> came
> back, the throttle body was soaking wet and ice cold to the touch. Then
> noticed the vacuum hose going to the PCV system was wet and cold as well.
> Followed the hose to a "T" where that T'd off went to the fuel vapor
> canister. I pulled that line to the canister off and vacuum plugged it.
> Problem solved...the vapor separator in the left wheel well was bad
> allowing fuel (after a fill up) to flow to the canister and on to the TB
> where it
> came in below the throttle plates. The excess fuel below the plates was
> changing physical state from liquid to a gas releasing a lot of heat and
> in
> turn making the TB cold enough to condense water out of the air...and also
> BTW making my engine run excessively rich.
>
> My point is.... is there something going on in the carb allowing excessive
> fuel to come in below the throttle plates and excessively cool things
> down?
> If nothing else works, maybe check that carb out. I would not have
> believed it if I hadn't seen it myself.
> --
> Larry
> 78 Royale w/500 Caddy
> Menomonie, WI.
>
> _______________________________________________
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.It would be nice to get some power to the house, looks like 3 or 4 more days.