Author Topic: Carb backfire - Sanity Check  (Read 1336 times)

Offline Marty73

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Carb backfire - Sanity Check
« on: October 20, 2017 - 02:27:55 pm »
So a couple years ago my 73 318 Challenger had an electrical problem and would no longer turn over/run/start/etc. No problem - I have to finish up the body work for paint. Fast forward to today and now it's time for paint, but I want to get it running again so I can easily move it around (and get it to the painter). After replacing all the engine bay harnesses, resistor, cap, coil, and all the other goodies I basically have a completely new ignition system. Still no joy - only to find out later (thanks to the forum!) that all power goes through the voltage gauge. One 25 dollar test light and the tightening of some screws and JOY! We have power/ignition again!

Next issue - now the car won't run (has fuel and spray) but continuously backfires through the carb. So need a sanity check

Original 318

Firing order should be 1-8-4-3-6-5-7-2
Distributer runs clockwise

During all the wiring replacement I did not remove or touch the distributer. TDC seems correct for the rotor pointing to #1 on the cap.

Any ideas? I've spent a couple days on this and can't figure it out.

Thanks in advance for any help!
Comin' at ya like a herd of turtles




Offline 73440

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Re: Carb backfire - Sanity Check
« Reply #1 on: October 20, 2017 - 07:54:15 pm »
https://www.holley.com/blog/post/troubleshooting_backfire_through_carburetor_/

Have you verified timing with a timing light ?
How does it run when revving the engine ?

If the carb has not been run for awhile , it may be out of adjustment.
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Offline Beekeeper

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Re: Carb backfire - Sanity Check
« Reply #2 on: October 20, 2017 - 08:00:10 pm »
I have had backfiring issues when the plug wires weren't connected to the right plugs, when the timing is way too far advanced, and also when their wasn't enough voltage going into the coil.

Offline 69bcuda

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Re: Carb backfire - Sanity Check
« Reply #3 on: October 21, 2017 - 09:04:03 am »
Lift the cap and inspect the coil contact for the rotor. Recheck Wire order.
Fouled plugs? Flooding?
Old fuel?
Check for obstruction in the exhaust.

Offline 734406pk

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Re: Carb backfire - Sanity Check
« Reply #4 on: October 22, 2017 - 09:34:57 am »
Quote: Firing order should be 1-8-4-3-6-5-7-2
Distributer runs clockwise

Check your plug wire arrangement on the distributor cap, make sure they are set clockwise as well starting with #1 cylinder.
1973 Challenger 440 6 pack auto 3.91 rear
2012 Dodge Ram 3500 dually 6.7 Cummins Fleece EFI Live
1973 Challenger 318 2bbl auto 2.73 rear 22.5 mpg RIP
1970 Challenger TA 340 4bbl auto-Sold and sad
1999 Dodge Ram 3500 dually 5.9 Cummins Fleece tuned VGT-sold
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Offline Marty73

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Re: Carb backfire - Sanity Check
« Reply #5 on: October 23, 2017 - 09:35:24 am »
Thanks guys - I checked the firing order and did find a pair reversed, but still have the same issue.

The car hadn't run for a couple years as I was chasing electrical issues. For the carb - it was "new" when I put it on, but I did de-gunk it since it sat for two years and all that seems good.

I can't get it running enough to check the timing, that and the timing bracket is missing (anyone got one for a 318 they way to part with?)

On the 2bbl Carter, I did 3 1/2 out on both jets, Fresh fuel in the tank. I ran the engine to TDC and made sure the rotor matched up on the distributor and used that as my start point for my spark plug wires. Pretty sure it was TDC on the compression stroke, but I will get a cylinder gauge to make sure.

May be a month or so until I can get back out to work on it again. Maybe I can sneak into the garage over the holidays...
Comin' at ya like a herd of turtles

Offline 734406pk

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Re: Carb backfire - Sanity Check
« Reply #6 on: October 23, 2017 - 09:46:02 am »
Are you using the original factory cast iron intake manifold with this 318?
1973 Challenger 440 6 pack auto 3.91 rear
2012 Dodge Ram 3500 dually 6.7 Cummins Fleece EFI Live
1973 Challenger 318 2bbl auto 2.73 rear 22.5 mpg RIP
1970 Challenger TA 340 4bbl auto-Sold and sad
1999 Dodge Ram 3500 dually 5.9 Cummins Fleece tuned VGT-sold
1995 Kawasaki ZX1100E & still alive

Offline 1 Wild R/T

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Re: Carb backfire - Sanity Check
« Reply #7 on: October 23, 2017 - 10:57:44 am »
Pull #1 spark plug (drivers front)  hold your finger over the hole (seal the hole) bump the starter till you feel compression... Now look at the timing marks & bring the mark on the damper up close to TDC....  Now look at your rotor..... Whee is it pointing? Thats where your #1 plug wire goes... As you know 1-8-4-3-6-5-7-2 clockwise...
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Offline Marty73

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Re: Carb backfire - Sanity Check
« Reply #8 on: October 23, 2017 - 03:57:26 pm »
Yep - original intake and original style Carter 2bbl
Comin' at ya like a herd of turtles

Offline 734406pk

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Re: Carb backfire - Sanity Check
« Reply #9 on: October 23, 2017 - 09:00:51 pm »
Ok your intake manifold was equipped with an EGR valve installed just below the throttle linkage, but before we get into that you need to be 110% sure your firing order and distributor phasing is correct as 1 Wild R/T has pointed out. also
Quote:   I can't get it running enough to check the timing, that and the timing bracket is missing (anyone got one for a 318 they way to part with?)

The timing indicator should be cast into the front cover, around 1:00 on the drivers side. Is this broken or missing?
1973 Challenger 440 6 pack auto 3.91 rear
2012 Dodge Ram 3500 dually 6.7 Cummins Fleece EFI Live
1973 Challenger 318 2bbl auto 2.73 rear 22.5 mpg RIP
1970 Challenger TA 340 4bbl auto-Sold and sad
1999 Dodge Ram 3500 dually 5.9 Cummins Fleece tuned VGT-sold
1995 Kawasaki ZX1100E & still alive

Offline Marty73

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Re: Carb backfire - Sanity Check
« Reply #10 on: October 26, 2017 - 08:29:52 am »
This is my first Mopar so maybe the timing cover is to dirty to see the casting. I'll get a flashlight and some cleaner and check - I was expecting there to be a bolt on pointer. My inexperience is showing  :bigsmile:

I'll double check TDC and spark plug cabling this weekend

Thanks Everyone!
Comin' at ya like a herd of turtles

Offline Marty73

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Re: Carb backfire - Sanity Check
« Reply #11 on: November 27, 2017 - 01:36:39 pm »
Thanks for the advise guys - with the some help in town over Thanksgiving (brother & nephew who are a lot better at this than I am)...

We found a couple issues

There appears to be an intake valve that is stuck open - that explains the backfire, so I'll be pulling the valve covers to see what is going on there. Hopefully I won't have to remove the head(s) - if so, well might as well get that engine swap going.

Jumped a tooth on the timing gear (maybe due to the backfire?) so timing was WAY off-

I got the dist turned enough to compensate for the jumped tooth. So now it wants to run, just got to get that valve un-stuck/closed

Once I get a spare warm day it's back into the garage.

thanks again for all the help!
Comin' at ya like a herd of turtles

Offline Beekeeper

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Re: Carb backfire - Sanity Check
« Reply #12 on: November 27, 2017 - 08:16:37 pm »
Thanks for the advise guys - with the some help in town over Thanksgiving (brother & nephew who are a lot better at this than I am)...

We found a couple issues

There appears to be an intake valve that is stuck open - that explains the backfire, so I'll be pulling the valve covers to see what is going on there. Hopefully I won't have to remove the head(s) - if so, well might as well get that engine swap going.

Jumped a tooth on the timing gear (maybe due to the backfire?) so timing was WAY off-

I got the dist turned enough to compensate for the jumped tooth. So now it wants to run, just got to get that valve un-stuck/closed

Once I get a spare warm day it's back into the garage.

thanks again for all the help!

I hate to say this but with those kind of issues, that engine sounds overdue for a good rebuild. Even with a new timing gear set to get the cam timing back to correct, you probably also need a rebuild on those heads. And if that's the case, the internals of that engine may also be on the brink of failure.

Offline Marty73

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Re: Carb backfire - Sanity Check
« Reply #13 on: November 30, 2017 - 10:27:22 am »
Yep - already checking for another engine. Might as well go 360 since that was the original plan anyway.

Right now I just need to get it running so I can get in/out of the garage so I can get the finish sanding on the body done.

Anyone got a cheap 360 LA long block/engine in the SC area?
Comin' at ya like a herd of turtles

Offline shadango

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Re: Carb backfire - Sanity Check
« Reply #14 on: January 10, 2018 - 01:29:39 pm »
Yep - already checking for another engine. Might as well go 360 since that was the original plan anyway.

Right now I just need to get it running so I can get in/out of the garage so I can get the finish sanding on the body done.

Anyone got a cheap 360 LA long block/engine in the SC area?

Just curious as to your progress...............