Home » Public Forums » GMCnet » [GMCnet] backfire!
| [GMCnet] backfire! [message #134876] |
Sat, 16 July 2011 21:53  |
Len Novak
Messages: 676
Registered: February 2004
Location: Las Vegas, NV
Karma: -3
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Senior Member |
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Now and then when I get on the gas the engine backfires, same after coming
off high revs when shutting down.
New plugs, but did it with the old plugs
Timing checks out
New cap and rotor
Any suggestions?
Len and Pat
78 Kingsley, The Beast II with dash lights that work
Fallbrook, CA
http://www.gmcmhphotos.com/photos/showgallery.php?cat=4375
www.bdub.net/novak/
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Len and Pat Novak
1978 GMC Kingsley
The Beast II with dash lights that work and labels you can see!
Las Vegas, NV new email: B52sRule@Gmail.com
http://www.gmcmhphotos.com/photos/showgallery.php?cat=4375
www.bdub.net/novak/
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| Re: [GMCnet] backfire! [message #134894 is a reply to message #134876] |
Sun, 17 July 2011 04:49  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
|
Senior Member |
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Lean mixture or signifigant vacuum leak, or perhaps a stretched timing
chain, all come to mind. I assume that you are referring to a popping back
through the carburetor and not a popping from the exhaust pipe, which
sometimes means that there is unburned fuel and oxygen enough present in the
exhaust to ignite.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Sat, Jul 16, 2011 at 7:53 PM, Len <B52Rule@adelphia.net> wrote:
> Now and then when I get on the gas the engine backfires, same after coming
> off high revs when shutting down.
>
>
>
> New plugs, but did it with the old plugs
>
>
>
> Timing checks out
>
>
>
> New cap and rotor
>
>
>
> Any suggestions?
>
>
>
> Len and Pat
> 78 Kingsley, The Beast II with dash lights that work
> Fallbrook, CA
>
> http://www.gmcmhphotos.com/photos/showgallery.php?cat=4375
>
> www.bdub.net/novak/
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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Unsubscribe or Change List Options:
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| Re: [GMCnet] backfire! [message #134914 is a reply to message #134894] |
Sun, 17 July 2011 09:06 |
Len Novak
Messages: 676
Registered: February 2004
Location: Las Vegas, NV
Karma: -3
|
Senior Member |
|
|
Nothing thru the carb, everything thru the exhaust
Len and Pat
78 Kingsley, The Beast II with dash lights that work
Fallbrook, CA
http://www.gmcmhphotos.com/photos/showgallery.php?cat=4375
www.bdub.net/novak/
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of James Hupy
Sent: Sunday, July 17, 2011 2:50 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] backfire!
Lean mixture or signifigant vacuum leak, or perhaps a stretched timing
chain, all come to mind. I assume that you are referring to a popping back
through the carburetor and not a popping from the exhaust pipe, which
sometimes means that there is unburned fuel and oxygen enough present in the
exhaust to ignite.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Sat, Jul 16, 2011 at 7:53 PM, Len <B52Rule@adelphia.net> wrote:
> Now and then when I get on the gas the engine backfires, same after coming
> off high revs when shutting down.
>
>
>
> New plugs, but did it with the old plugs
>
>
>
> Timing checks out
>
>
>
> New cap and rotor
>
>
>
> Any suggestions?
>
>
>
> Len and Pat
> 78 Kingsley, The Beast II with dash lights that work
> Fallbrook, CA
>
> http://www.gmcmhphotos.com/photos/showgallery.php?cat=4375
>
> www.bdub.net/novak/
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Len and Pat Novak
1978 GMC Kingsley
The Beast II with dash lights that work and labels you can see!
Las Vegas, NV new email: B52sRule@Gmail.com
http://www.gmcmhphotos.com/photos/showgallery.php?cat=4375
www.bdub.net/novak/
|
|
|
|
| Re: [GMCnet] backfire! [message #134915 is a reply to message #134914] |
Sun, 17 July 2011 09:19 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
|
Senior Member |
|
|
Len, does your backfire happen at a steady speed or on accelleration, or
perhaps decelleration? Spark plug wire induction flashover caused from
running the plug wires parallel to each other in too close proximity to each
other will cause symptoms like you describe. Make sure thay are separated by
at least a half inch or more. If they are old or very dusty/dirty, replace
them with a good silicone insulated set. When the engine is under
accelerration at part throttle you will often experience lean misfire with a
Quadrajet Carb, particularly if the spark plug gaps are too wide. Make sure
that they are not wider than .045".
Carbon tracking on the rotor or inside the distributor cap can also cause
the same problem. I know, lots of stuff to check. Be systematic, check one
thing at a time, it is usually blatantly obvious when you discover the
cause. Such is the fate of a GMC tech.<Grin>
Jim Hupy
Salem, OR
78 GMC Royale 403
On Sun, Jul 17, 2011 at 7:06 AM, Len <B52Rule@adelphia.net> wrote:
> Nothing thru the carb, everything thru the exhaust
>
> Len and Pat
> 78 Kingsley, The Beast II with dash lights that work
> Fallbrook, CA
>
> http://www.gmcmhphotos.com/photos/showgallery.php?cat=4375
>
> www.bdub.net/novak/
>
>
>
>
> -----Original Message-----
> From: gmclist-bounces@temp.gmcnet.org
> [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of James Hupy
> Sent: Sunday, July 17, 2011 2:50 AM
> To: gmclist@temp.gmcnet.org
> Subject: Re: [GMCnet] backfire!
>
> Lean mixture or signifigant vacuum leak, or perhaps a stretched timing
> chain, all come to mind. I assume that you are referring to a popping back
> through the carburetor and not a popping from the exhaust pipe, which
> sometimes means that there is unburned fuel and oxygen enough present in
> the
> exhaust to ignite.
> Jim Hupy
> Salem, OR
> 78 GMC Royale 403
>
> On Sat, Jul 16, 2011 at 7:53 PM, Len <B52Rule@adelphia.net> wrote:
>
> > Now and then when I get on the gas the engine backfires, same after
> coming
> > off high revs when shutting down.
> >
> >
> >
> > New plugs, but did it with the old plugs
> >
> >
> >
> > Timing checks out
> >
> >
> >
> > New cap and rotor
> >
> >
> >
> > Any suggestions?
> >
> >
> >
> > Len and Pat
> > 78 Kingsley, The Beast II with dash lights that work
> > Fallbrook, CA
> >
> > http://www.gmcmhphotos.com/photos/showgallery.php?cat=4375
> >
> > www.bdub.net/novak/
> >
> >
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] backfire! [message #134920 is a reply to message #134915] |
Sun, 17 July 2011 10:28 |
Len Novak
Messages: 676
Registered: February 2004
Location: Las Vegas, NV
Karma: -3
|
Senior Member |
|
|
More on acceleration, but most noticeable, when I back off the throttle or
shut the engine off
New rotor, cap, module, the wires are properly separated
I checked all the vacuum lines and all is well
They are so loud that they blow the runt off the exhaust system, but I have
to replace that anyway!
Len and Pat
78 Kingsley, The Beast II with dash lights that work
Fallbrook, CA
http://www.gmcmhphotos.com/photos/showgallery.php?cat=4375
www.bdub.net/novak/
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of James Hupy
Sent: Sunday, July 17, 2011 7:20 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] backfire!
Len, does your backfire happen at a steady speed or on accelleration, or
perhaps decelleration? Spark plug wire induction flashover caused from
running the plug wires parallel to each other in too close proximity to each
other will cause symptoms like you describe. Make sure thay are separated by
at least a half inch or more. If they are old or very dusty/dirty, replace
them with a good silicone insulated set. When the engine is under
accelerration at part throttle you will often experience lean misfire with a
Quadrajet Carb, particularly if the spark plug gaps are too wide. Make sure
that they are not wider than .045".
Carbon tracking on the rotor or inside the distributor cap can also cause
the same problem. I know, lots of stuff to check. Be systematic, check one
thing at a time, it is usually blatantly obvious when you discover the
cause. Such is the fate of a GMC tech.<Grin>
Jim Hupy
Salem, OR
78 GMC Royale 403
On Sun, Jul 17, 2011 at 7:06 AM, Len <B52Rule@adelphia.net> wrote:
> Nothing thru the carb, everything thru the exhaust
>
> Len and Pat
> 78 Kingsley, The Beast II with dash lights that work
> Fallbrook, CA
>
> http://www.gmcmhphotos.com/photos/showgallery.php?cat=4375
>
> www.bdub.net/novak/
>
>
>
>
> -----Original Message-----
> From: gmclist-bounces@temp.gmcnet.org
> [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of James Hupy
> Sent: Sunday, July 17, 2011 2:50 AM
> To: gmclist@temp.gmcnet.org
> Subject: Re: [GMCnet] backfire!
>
> Lean mixture or signifigant vacuum leak, or perhaps a stretched timing
> chain, all come to mind. I assume that you are referring to a popping back
> through the carburetor and not a popping from the exhaust pipe, which
> sometimes means that there is unburned fuel and oxygen enough present in
> the
> exhaust to ignite.
> Jim Hupy
> Salem, OR
> 78 GMC Royale 403
>
> On Sat, Jul 16, 2011 at 7:53 PM, Len <B52Rule@adelphia.net> wrote:
>
> > Now and then when I get on the gas the engine backfires, same after
> coming
> > off high revs when shutting down.
> >
> >
> >
> > New plugs, but did it with the old plugs
> >
> >
> >
> > Timing checks out
> >
> >
> >
> > New cap and rotor
> >
> >
> >
> > Any suggestions?
> >
> >
> >
> > Len and Pat
> > 78 Kingsley, The Beast II with dash lights that work
> > Fallbrook, CA
> >
> > http://www.gmcmhphotos.com/photos/showgallery.php?cat=4375
> >
> > www.bdub.net/novak/
> >
> >
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Len and Pat Novak
1978 GMC Kingsley
The Beast II with dash lights that work and labels you can see!
Las Vegas, NV new email: B52sRule@Gmail.com
http://www.gmcmhphotos.com/photos/showgallery.php?cat=4375
www.bdub.net/novak/
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