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Old 08-12-2017, 07:20 PM   #1
61Chevy454
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Sudden backfire and won't start until I adjust AFR

So, I go to start my 454 with an Edelbrock 750 on it and it doesn't start...the starter hangs up like it's too advanced and backfires through the carb. I adjust the carb mixture a bit richer and it starts up and runs a bit shakier than usual, but still drives fine.

I get home, adjust the idle mixture again and the shake is gone and it runs fine, just like normal.

Should I be worried or no?
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Old 08-12-2017, 07:52 PM   #2
geezer#99
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Re: Sudden backfire and won't start until I adjust AFR

What do you mean by 'adjust the carb mixture'?
If you mean the mixture screws, those are only for idle.
Was the motor cold or hot when you started it?
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Old 08-12-2017, 07:54 PM   #3
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Re: Sudden backfire and won't start until I adjust AFR

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Originally Posted by geezer#99 View Post
What do you mean by 'adjust the carb mixture'?
If you mean the mixture screws, those are only for idle.
Was the motor cold or hot when you started it?
I had to adjust the idle mixture to make it start and run.

It was in the middle. It had been sitting for at least 30 minutes, if not more.
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Old 08-12-2017, 08:00 PM   #4
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Re: Sudden backfire and won't start until I adjust AFR

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Originally Posted by 61Chevy454 View Post
I had to adjust the idle mixture to make it start and run.

It was in the middle. It had been sitting for at least 30 minutes, if not more.
Now you got me confused!
Adjusting mix screws shouldn't change starting.

What was 'in the middle'?

What's your initial timing?
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Old 08-12-2017, 08:02 PM   #5
61Chevy454
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Re: Sudden backfire and won't start until I adjust AFR

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Originally Posted by geezer#99 View Post
Now you got me confused!
Adjusting mix screws shouldn't change starting.

What was 'in the middle'?

What's your initial timing?
I know! That's why I don't think it jumped timing or anything.

The motor wasn't warmed up or totally cooled down, so it was "in the middle" per se.

16*
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Old 08-12-2017, 08:09 PM   #6
geezer#99
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Re: Sudden backfire and won't start until I adjust AFR

Pop the dizzy cap and check the weights aren't hung up.
Did you check your timing?
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Old 08-12-2017, 08:10 PM   #7
61Chevy454
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Re: Sudden backfire and won't start until I adjust AFR

Quote:
Originally Posted by geezer#99 View Post
Now you got me confused!
Adjusting mix screws shouldn't change starting.

What was 'in the middle'?

What's your initial timing?
Quote:
Originally Posted by geezer#99 View Post
Pop the dizzy cap and check the weights aren't hung up.
Did you check your timing?
Didn't check my timing today, but it was retimed in the past 2 months
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Old 08-12-2017, 08:21 PM   #8
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Re: Sudden backfire and won't start until I adjust AFR

Lean and retarded makes backfires!
Perhaps the fuel was all boiled out of your carb from heat and contributed to the backfire.
Do you have a heat plate under your carb?
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Old 08-12-2017, 08:27 PM   #9
61Chevy454
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Re: Sudden backfire and won't start until I adjust AFR

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Originally Posted by geezer#99 View Post
Lean and retarded makes backfires!
Perhaps the fuel was all boiled out of your carb from heat and contributed to the backfire.
Do you have a heat plate under your carb?
I have a half-inch wooden carb spacer.

I figured it could have been the fuel boil. I just wanted to make sure my motor wasn't about to **** itself or anything.
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Old 08-12-2017, 08:46 PM   #10
geezer#99
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Re: Sudden backfire and won't start until I adjust AFR

Coulda been a one time thing.
I had a bbf 460 that coughed every time it started.
If it does it again just look in the carb venturi first to see if you have any fuel.
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