Onan carb frosting

J

jerry sitzlar

New member
Mar 6, 2013
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Sounds like the carb is running too rich. Dirty air filter? Wet ignition?

Jerry
--
Jerry Sitzlar..... 77 Eleganza II, Twin bed, dry bath......
Lenoir City, TN
 
> 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

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 - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
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.
 
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 <

> 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*
 
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 <

>
> > 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*
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com
 
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.
 
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
 
Uh, DON'T go adjusting...

--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
 
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

>
> 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
 
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

> 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 <

> >
> > 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
>
 
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
 
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.
 
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.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
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