| [GMCnet] Onan backfire diagnostics [message #143049] |
Mon, 12 September 2011 02:12  |
Douglas Norton
Messages: 191
Registered: April 2008
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So, my Onan quit during a 15 minute test run and would not restart except to backfire a lot. It backfired a couple of times and quit and would not start. I added fuel to the tank and it started but after a minute it began to kick and backfire. I changed plugs but the old ones had 15 minutes on them. The were very white and clean. The gen was running very hot too. I checked fuel and the pump put out 4 ounces in under 30 seconds. That works out to over 4 gallons an hour or many times possible demand.
The backfires came out the exhaust, some with flames, some black, some white, and some very loud. Before looking for a stuck valve or problem ignition, I will look to cleaning the carb.
1. If I am on the right track and will I need a kit?
2. are rebuilt Onan carbs available (Jim K is my first choice for a source if I fail a rebuild)
3. Some unnamed diy mechanic forgot he removed the fuel filter while making an emergency fuel line replacement a couple of years ago; do you think that mattered?
4. would a petronix upgrade be worth it?
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| Re: [GMCnet] Onan backfire diagnostics [message #143050 is a reply to message #143049] |
Mon, 12 September 2011 02:18  |
 |
mike miller
Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon
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| Douglas Norton wrote on Mon, 12 September 2011 00:12 |
...
4. would a petronix upgrade be worth it?
|
yep.
Even if your Onan ran perfectly, it would be worth it.
Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo'
http://m000035.blogspot.com
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| Re: [GMCnet] Onan backfire diagnostics [message #143053 is a reply to message #143050] |
Mon, 12 September 2011 04:11 |
Douglas Norton
Messages: 191
Registered: April 2008
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Thanks Mike. I think there was some crud in the seat below the needle and I cleaned that out. In the process, I messed up a small O ring - probably hardened by ethanol. Looks to me like the mixture can be adjusted from the outside using the needle screw that little O ring was on. I guess it is a simple purchase from an auto parts store - hope so. I will look to ordering the petronix parts, I saved several messages from those who did the mod so I could do it when ready. Jim K, do you sell a kit?
--- On Mon, 9/12/11, Mike Miller <m000035@gmail.com> wrote:
From: Mike Miller <m000035@gmail.com>
Subject: Re: [GMCnet] Onan backfire diagnostics
To: gmclist@temp.gmcnet.org
Date: Monday, September 12, 2011, 12:18 AM
Douglas Norton wrote on Mon, 12 September 2011 00:12
> ...
> 4. would a petronix upgrade be worth it?
yep.
Even if your Onan ran perfectly, it would be worth it.
--
Mike Miller -- Hillsboro, OR -- on the Black list
(#1)'73 26' exPainted D. -- (#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
http://m000035.blogspot.com
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| Re: [GMCnet] Onan backfire diagnostics [message #143055 is a reply to message #143053] |
Mon, 12 September 2011 05:23 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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HI Doug
did you read all of this ;>)
http://gmcmotorhome.info/list.html#GEN
gene
On Mon, Sep 12, 2011 at 2:11 AM, Douglas Norton <nortocd@yahoo.com> wrote:
> Thanks Mike. I think there was some crud in the seat below the needle and
> I cleaned that out. In the process, I messed up a small O ring - probably
> hardened by ethanol. Looks to me like the mixture can be adjusted from the
> outside using the needle screw that little O ring was on. I guess it is a
> simple purchase from an auto parts store - hope so. I will look to ordering
> the petronix parts, I saved several messages from those who did the mod so I
> could do it when ready. Jim K, do you sell a kit?
>
> --- On Mon, 9/12/11, Mike Miller <m000035@gmail.com> wrote:
>
> From: Mike Miller <m000035@gmail.com>
> Subject: Re: [GMCnet] Onan backfire diagnostics
> To: gmclist@temp.gmcnet.org
> Date: Monday, September 12, 2011, 12:18 AM
>
>
>
> Douglas Norton wrote on Mon, 12 September 2011 00:12
> > ...
> > 4. would a petronix upgrade be worth it?
>
>
> yep.
>
> Even if your Onan ran perfectly, it would be worth it.
> --
> Mike Miller -- Hillsboro, OR -- on the Black list
> (#1)'73 26' exPainted D. -- (#2)`78 23' Birchaven Rear Bath -- (#3)`77 23'
> Birchaven Side Bath
> http://m000035.blogspot.com
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> _______________________________________________
> GMCnet mailing list
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--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: [GMCnet] Onan backfire diagnostics [message #143056 is a reply to message #143049] |
Mon, 12 September 2011 06:12 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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On Sep 12, 2011, at 3:12 AM, Douglas Norton wrote:
> So, my Onan quit during a 15 minute test run and would not restart except to backfire a lot. It backfired a couple of times and quit and would not start. I added fuel to the tank and it started but after a minute it began to kick and backfire. I changed plugs but the old ones had 15 minutes on them. The were very white and clean. The gen was running very hot too. I checked fuel and the pump put out 4 ounces in under 30 seconds. That works out to over 4 gallons an hour or many times possible demand.
>
> The backfires came out the exhaust, some with flames, some black, some white, and some very loud. Before looking for a stuck valve or problem ignition, I will look to cleaning the carb.
>
> 1. If I am on the right track and will I need a kit?
> 2. are rebuilt Onan carbs available (Jim K is my first choice for a source if I fail a rebuild)
> 3. Some unnamed diy mechanic forgot he removed the fuel filter while making an emergency fuel line replacement a couple of years ago; do you think that mattered?
> 4. would a petronix upgrade be worth it?
Hello Doug
I would suspect that it is the adjustment of the points.
But I would also check the O ring on the high speed adjustment needle. It is located in the bottom of the filter bowl at the bottom of the carb. These often crack and then you cannot get the proper mixture. If that is damaged it will run way too rich and often will have the symtoms that you mention. It is a flat sided "O" ring but just replace it with a 1/4" OD / 1/8" ID round O ring that you can get at about any hardware store or auto parts store.
What fuel filter are you talking about? There isn't any except the small screen in the bowl at the bottom of the carb. Do you by chance mean the fuel shut off solenoid loacated just before the fuel pump?
The petronix will indeed make it run better.
Emery Stora
77 Kingsley
Santa Fe, NM
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| Re: [GMCnet] Onan backfire diagnostics [message #143058 is a reply to message #143049] |
Mon, 12 September 2011 06:36 |
emerystora
Messages: 4442
Registered: January 2004
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On Sep 12, 2011, at 3:12 AM, Douglas Norton wrote:
> So, my Onan quit during a 15 minute test run and would not restart except to backfire a lot. It backfired a couple of times and quit and would not start. I added fuel to the tank and it started but after a minute it began to kick and backfire. I changed plugs but the old ones had 15 minutes on them. The were very white and clean. The gen was running very hot too. I checked fuel and the pump put out 4 ounces in under 30 seconds. That works out to over 4 gallons an hour or many times possible demand.
>
> The backfires came out the exhaust, some with flames, some black, some white, and some very loud. Before looking for a stuck valve or problem ignition, I will look to cleaning the carb.
>
> 1. If I am on the right track and will I need a kit?
> 2. are rebuilt Onan carbs available (Jim K is my first choice for a source if I fail a rebuild)
> 3. Some unnamed diy mechanic forgot he removed the fuel filter while making an emergency fuel line replacement a couple of years ago; do you think that mattered?
> 4. would a petronix upgrade be worth it?
Forgot to say in my last email that you should set the points to a gap of .020"
Also on the high speed jet, after you replace the O ring use an initial setting of 1-1/4 turns open from the fully closed position.
The idle jet should start with a one turn open.
Emery Stora
77 Kingsley
Santa Fe, NM
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| Re: [GMCnet] Onan backfire diagnostics [message #143070 is a reply to message #143049] |
Mon, 12 September 2011 09:04 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Several things could cause your problem. The first thing to do is determine if it is fuel or ignition. I seriously doubt it fuel but there is as filter in the bottom of the fuel pump. Twist the nut on the bottom of the fuel pump and the cap will fall off. The filter should fall out at that point. Also the o-ring you are talking about is a hardware store item. Emery, in the past, posted the size. I believe it is 1/8" ID - 1/4" OD but check with Emery if that size does not work. Jim K. did in the past did stock the filter. The mesh one is cleanable the stone one usually you just replace.
I would take a timing light and look at the timing. If it is ignition, then the line will be jumping all over the place or occasionally missing. I'm guessing this is your problem and the points probably need to be adjusted or replaced.
The Pertronix is a good upgrade for this problem, but I would still get it running on the points so you have a back up ignition source if the Pertronix were ever to quit. You can not run both at the same time but you only need to move on wire to switch between the two sources. Jim K. mentioned he was putting a kit together. I do not know if he ever completed that project or not. Check with Jim K.
Emery just stopped by my coach and verified that the O-ring is 1/4" OD by 1/8" ID. He also said he posted something on this earlier today so much of this posting may be duplicated information.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan backfire diagnostics [message #143313 is a reply to message #143049] |
Wed, 14 September 2011 10:18 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Wouldn't the white plugs indicate lean?
Also the coil could be heat sensitive failing. You could have the murder mystery multiple problems syndrome.
John Lebetski
Woodstock, IL
77 Eleganza II
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