Author Topic: Back Fire  (Read 2063 times)

Offline Locadd

  • Posts: 8
Back Fire
« on: June 29, 2008, 05:43:30 AM »
Hi from Down Under
My 67 Coupe back fires after you take your foot of the gas Pump while sitting , it takes reves without any trouble but as soonas you take your foot of it it back fires quite bad, does any one have any advice as to why this is happening?
Cheers Locadd
Australia
Peter
1967 Deville Coupe

Online The Tassie Devil(le)

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  • Name: Bruce Reynolds
Re: Back Fire
« Reply #1 on: June 29, 2008, 05:59:12 AM »
G'day Peter,

I am understanding it is backfiring out the Exhaust and not the Carby?

Out the Exhaust is a sign of the mixture running very Rich, and the Carby, just the opposite, running very lean.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

Offline TJ Hopland

  • Posts: 10188
Re: Back Fire
« Reply #2 on: June 29, 2008, 04:05:49 PM »
What Bruce said...

Look to make sure choke is doing what its supposed to be doing.
Check change/fuel filter(s)
Could be a float or needle/seat issue in the carb

I have been reading about a lot of fuel system issues on older cars lately.  I suspect its because alcohol blends are becoming more common in more areas and the 'old' rubber parts are even older than they were when we got the blends in my area 10+ years ago.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Re: Back Fire
« Reply #3 on: June 29, 2008, 07:12:08 PM »
Locadd (M'Lad)
If this is a 66 with the California emissions air pump, chances are that the diverter valve is not functioning.  It's the device (that is supposed to be) on top of the air pump, and has a vacuum signal to it so that upon deceleration (car and engine) the air is "dumped" and not sent to the engine. 
I would first check to see if the vacuum line is connected (at both ends) and solid, then I would check by applying a vacuum to the connection of the dump valve and verifying that it doesn't leak (won't hold a vacuum) and that something works.
This valve, if you want to maintain the system and if you have the air pump on your engine and I haven't wasted a lot of Bytes, is still available.
Let us know
Greg
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Offline Locadd

  • Posts: 8
Re: Back Fire
« Reply #4 on: June 30, 2008, 03:15:28 AM »
Hi Greg,
Thanks for your info, it is a 67 California car, Can this air system be removed from the engine without any dramas and will it effect the way the car runs if removed?
Any info will be great
Cheers
Locadd
Downunder
« Last Edit: July 01, 2008, 02:14:04 PM by Tom Hall 7485 »
Peter
1967 Deville Coupe

Offline TJ Hopland

  • Posts: 10188
Re: Back Fire
« Reply #5 on: June 30, 2008, 09:23:49 AM »
I would just weigh the difference in cost for repair vs. removal. If the smog system is the same as the 68- motors its not a big deal to unhook and plug the air lines the problem comes in getting the belts routed without the pump.  Often times you need a different set of pulleys to get the belts all aligned.    What kills the systems other than age is the check valves start leaking and letting exhaust into the diverter and pump.  The corrosive exhaust kills the stuff.  To check the check valve just pull the hose off and see if exhaust comes out.  The valves are fairly standard and cheap because they were used till at least the mid 80's.  The valve and pump can be checked like greg said.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Re: Back Fire
« Reply #6 on: June 30, 2008, 05:13:51 PM »
Also, a worn timing chain will change the timing between accelleration and decelleration.
71 Olds 98 LS, 66 Fairlane 500 XL Convertible, 55 Packard Clipper Super, 58 Edsel Ranger, 72 Cheyenne Super, many 49-60 parts cars, abandoned "House Of Doom" full of 49-60 parts. Huge piles of engine parts, brackets, tin, Hydramatic & Jetaway parts,  thousands of stainless moldings, dozens of perfect sedan doors.

Re: Back Fire
« Reply #7 on: June 30, 2008, 08:37:39 PM »
Locadd,
Yes you can remove all the air injection devices and re jet the carb with minimal effort.  Does your (429) engine have a pulley for the air pump by itself, or is something else on the belt that drives the air pump.  There were several methods of driving this device.
If it is driven separately, you can test for the cause of the backfire by simply removing the belt, so the pump will not turn. Then see if your backfiring condition is still there.
An alternate method of testing the pump's effect would be to remove the large rubber hose from the pump discharge, and temporarily plug the metal "wye" pipe.  If the back firing continues, you problem may be elsewhere.
Let us know
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Offline Locadd

  • Posts: 8
Re: Back Fire
« Reply #8 on: July 01, 2008, 12:47:29 AM »
Thanks cadillac kid
I will give this a try when i fly back into town this week and see how it goes, will post an update when i have tried it
Cheers Locadd
« Last Edit: July 01, 2008, 02:14:44 PM by Tom Hall 7485 »
Peter
1967 Deville Coupe

Offline Locadd

  • Posts: 8
Re: Back Fire
« Reply #9 on: July 07, 2008, 12:18:27 AM »
Hi all,
I have removed the belt from the air pump drive and i now have no more back firering
« Last Edit: July 08, 2008, 09:07:42 AM by Tom Hall 7485 »
Peter
1967 Deville Coupe

 

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