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Sudden back firing issue when starting when engine warm
#1
It was a beautiful day so took the Mustang out for a drive. No issues starting cold but twice to day had issues starting it after it was warm. Both times car didn't start first cranking attempt but upon second try started right up but back fired...then ran great after starting. Engine was warm but not hot and didn't back fire or have any issues when starting it early when cold. Suggestions?

Jim

M code 71 Mach 1, 351 4V Cleveland, Ram Air (not factory), C6 Trans, 3.5 rear
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#2
Could use a little more info. Did you change anything before this started?

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
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#3
marks73;65990 Wrote:Could use a little more info. Did you change anything before this started?

Nope, that's the confusing part, not sure what brought it on but I haven't really been driving it much due to the weather. The last thing I changed were the plugs but I have about a 500 miles on them with no issues. It runs fine after starting. The fact that it doesn't attempt to start until the second cranking then starts right up (with a back fire) is baffling.

Jim

M code 71 Mach 1, 351 4V Cleveland, Ram Air (not factory), C6 Trans, 3.5 rear
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#4
Timing
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#5
Through the carb, or out the exhaust?

1973 Mach 1 Q code 351 4V, 9A paint, standard interior, 3.50 rear, C6 trans.
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#6
Tnfastbk;66015 Wrote:Timing

{thumbs up} ..Check timing..then keep trouble shooting from there.
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#7
If it backfired through the carb, it would either be timing or a fuel issue. Possible blown power valve if it's a Holley wih the older style valve, without the backfire protection.
If it was out the exhaust, then that means raw fuel got past the cylinder. If you did nothing different, then I'd say you have a fuel issue.
If it cranks right over and doesn't role slow when you crank it, kind of a similar crank to when a starter solenoid is going out, then it's probably not timing.
Maybe you got some bad fuel and it just didn't lie it. I'd change the fuel filter and add some Chevron super unleaded and maybe some Redline SI-I Injector Cleaner if you can get your hands on a bottle. If you do all that, and it does it again, I'd say you illiminated fuel.




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#8
Totalled;66041 Wrote:Through the carb, or out the exhaust?

Through the exhaust, drivers side both times.

guys72Mach1;66047 Wrote:.
If it cranks right over and doesn't role slow when you crank it, kind of a similar crank to when a starter solenoid is going out, then it's probably not timing.
Maybe you got some bad fuel and it just didn't lie it. I'd change the fuel filter and add some Chevron super unleaded and maybe some Redline SI-I Injector Cleaner if you can get your hands on a bottle. If you do all that, and it does it again, I'd say you illiminated fuel.

It cranks rapidly but it's as if it's not firing, when I crack the second time it fires right up with the backfire out the exhaust then runs OK. I've tried a couple more times since my initial post and I still have the issue with it not starting the first time I crank but starts on the second attempt, no backfire this time.

Timing or running to lean? Lots of leads for me to check out.

Jim

M code 71 Mach 1, 351 4V Cleveland, Ram Air (not factory), C6 Trans, 3.5 rear
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#9
Out the back is definetly fuel. Timing would be back through the carb.
Sounds like maybe the float is stuck, or maybe something dirty got in your carb and is clogging a port.
What kind of carb is it?




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#10
guys72Mach1;66061 Wrote:Out the back is definetly fuel. Timing would be back through the carb.
Sounds like maybe the float is stuck, or maybe something dirty got in your carb and is clogging a port.
What kind of carb is it?

Edlebrock thunder series, less than 6 months old.

Jim

M code 71 Mach 1, 351 4V Cleveland, Ram Air (not factory), C6 Trans, 3.5 rear
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