Author Topic: Backfire  (Read 5964 times)

GT350AUS

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Backfire
« on: April 16, 2019, 04:50:47 PM »
I started the topic because it morphed from an earlier one re correct spark plugs and has had me chasing a backfire in my KR.

So in summary:

Engine starts, idles and cruises fine but it backfires when accelerating harder than just cruising.

Car was running fine until i had it stored in a workshop for 3 years slowly getting some work done when it developed a backfire once it was started.

Had the carby rebuilt

Changed points, condenser and coil, set timing, checked number of spark plugs and they’re fine no sign of wear or fouling and the problem is still there.

Could be a vacuum leak causing engine to run to lean

Tilt away was fixed by changing the relay but now the relay is working but the tilt away wont tilt back so I’m thinking there’s a vacuum problem in the system which could be related back to the backfire.

A couple of guys on the forum have offered some assistance which is much appreciated, thanks Shelbydoug and 1967 eight barrel

So this is the current position, I’m going to chase down a vacuum leak as my next step,

If anyone else has had a similar issue your feedback would be appreciated by me and also to assist for anyone else who may experience the same issue in the future.

Ross


« Last Edit: April 16, 2019, 06:32:44 PM by GT350AUS »

Rickmustang

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Re: Backfire
« Reply #1 on: April 16, 2019, 08:06:13 PM »
Easy stuff first. Change your cap and rotor. Solved my problem.
1965 G.T. 350
1967 Fairlane GT - 390 4-speed
1970 Mach 1 - 428CJ 4-speed/AC
1971 Mach 1 - 429CJ auto/AC
2005 Ford GT

GT350AUS

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Re: Backfire
« Reply #2 on: April 16, 2019, 08:14:45 PM »
Cap and rotor changed also

Sorry forgot to mention that.


shelbydoug

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Re: Backfire
« Reply #3 on: April 16, 2019, 08:24:49 PM »
Bring it in. I'll fix it for free. :D
68 GT350 Lives Matter!

GT350AUS

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Re: Backfire
« Reply #4 on: April 16, 2019, 08:38:54 PM »
Come to Australia I'll put you up for free  ;)

shelbydoug

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Re: Backfire
« Reply #5 on: April 16, 2019, 08:50:14 PM »
Come to Australia I'll put you up for free  ;)

Let me get my Google driving instructions.
68 GT350 Lives Matter!

GT350AUS

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Re: Backfire
« Reply #6 on: April 16, 2019, 09:22:32 PM »
Cool

I'll have cold beer waiting for you.

Ross

Rickmustang

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Re: Backfire
« Reply #7 on: April 16, 2019, 10:47:46 PM »
Timing or carb issue is about all that's left. Would have to be a big vacuum leak....
1965 G.T. 350
1967 Fairlane GT - 390 4-speed
1970 Mach 1 - 428CJ 4-speed/AC
1971 Mach 1 - 429CJ auto/AC
2005 Ford GT

shelbydoug

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Re: Backfire
« Reply #8 on: April 17, 2019, 06:56:20 AM »
At this point, after installing a vacuum gauge, I'd disconnect the vacuum cannister for the tilt column and plug the hoses. Run the car. See if the problem goes away.

68 GT350 Lives Matter!

Greg

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Re: Backfire
« Reply #9 on: April 17, 2019, 08:05:20 AM »
I would go back to the carb.  Just because it was rebuilt doesn't mean it was rebuilt correctly.  Get a new or proven carb, put it on and try it before you do anything else.  I suspect that is where your problem is.
Shelby's and Fords from Day 1

texas swede

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Re: Backfire
« Reply #10 on: April 17, 2019, 09:09:26 AM »
Does the car have Thermactor System? If so, it could be the backfire valve.
Another problem causing this can be the float level in the carb.
Texas Swede

GT350AUS

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Re: Backfire
« Reply #11 on: April 17, 2019, 09:49:38 AM »
No thermactor system fitted. It was removed before my time.

Float level is set correctly.

Thanks for your suggestions.

PR

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Re: Backfire
« Reply #12 on: April 17, 2019, 10:44:53 PM »
Go back to the basics, your missing something, it is a very simple system

GT350AUS

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Re: Backfire
« Reply #13 on: April 17, 2019, 10:53:49 PM »
Go back to the basics, your missing something, it is a very simple system

Yep I agree...its probably staring at me but I can't see the forest  because of the trees....LOL

Once I get it sorted I'll post back on the forum.

Side-Oilers

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Re: Backfire
« Reply #14 on: April 18, 2019, 12:02:43 AM »
I realize a stumble is different from a backfire, but I would still take another look at things that can cause both:

Carb, fuel filter, bad fuel, fouled spark plug(s), bad ignition wire(s).

You wrote that you checked a number of spark plugs. I'd check and replace them all.  Yes, it's a pain, but the one plug you don't check or change will always be the bad one. 
« Last Edit: April 18, 2019, 12:27:31 AM by Side-Oilers »
Current:
2006 FGT. Tungsten. Whipple, HRE 20s, Ohlin coil-overs, 3.90 gears. 210.7 mph.

Kirkham Cobra. 482-inch aluminum side-oiler. Tremec 5-spd.

Formerly:
1968 GT500KR #2575 (1982-2022)
1970 Ranchero GT 429
1969 LTD Country Squire 429
1963 T-Bird Sport Roadster
1957 T-Bird E-model 3-spd stick