Backfiring 460
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Senior User
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From: Enid, OK
Backfiring 460
I have a 1979 F 150 with a 460 and holley 4 barrel. It starts okay but you have to feather the throttle to get it to take off from idle. If I step on the gas too hard it stumbles and will backfire through the carb. It seems to run okay at higher rpms but will backfire on hard acceleration.
Moderator
Joined: Dec 2001
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From: Louisville,Ky.
Sounds like either your accelerator pump is stuck/gummed up or is out of adjustment. Did it just start doing it out of the blue? Is the vacuum advance working properly? What list# Holley is it? The number should be stamped on the front of the choke housing towards the drivers side.
Tuned
Joined: Feb 2003
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From: Cincinnati, Ohio
Check to make sure the fuel bowl float level is set correctly and that you are not dripping out of either bowl because they are set too high. Not saying this your problem but I had a similar problem and found that the secondary fuel bowl level was set too high.
John
John
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From: Enid, OK
I will look at the list number today. My truck is in storage 30 miles away so I get to visit on the weekends.
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Cargo Master
Joined: Dec 2004
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From: NE Texas
Start by checking your timing and make sure that the mechanical advance is working. Check the vac advance while you're there, although if it is bad it would not contribute to this particular problem.
Secondly, look down the throat of the carb and snap the throttle open. You should see a nice, strong stream of gas squirt into both primary throats. If it is squirting, check the accelerator pump linkage to see that there is no more than about .020" of free play between the acc pump lever and the actuating arm.
If none of this turns up a problem, you will need to go deeper into the carb. Post the results here, and we will continue the troubleshooting procedure.
Good luck,
Doc
ASE Master
Secondly, look down the throat of the carb and snap the throttle open. You should see a nice, strong stream of gas squirt into both primary throats. If it is squirting, check the accelerator pump linkage to see that there is no more than about .020" of free play between the acc pump lever and the actuating arm.
If none of this turns up a problem, you will need to go deeper into the carb. Post the results here, and we will continue the troubleshooting procedure.
Good luck,
Doc
ASE Master
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i checked everything it it seems fine, timinmg, pump etc. i changed the alternator to see if the power to auto choke wasnt good. it seemed to make a little difference but as the truck ran the plugs got fouled after 5 mins, started backfiring and sputtering again
Senior User
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From: Visalia, California
Originally Posted by Arnold Kenyon
I have a 1979 F 150 with a 460 and holley 4 barrel. It starts okay but you have to feather the throttle to get it to take off from idle. If I step on the gas too hard it stumbles and will backfire through the carb. It seems to run okay at higher rpms but will backfire on hard acceleration.
If you're getting backfire you've got valves open at the wrong time.
Double and triple check your timing. Be sure when you set your initial timing it's with the vacuum advance disconnected and the vacuum line is plugged. Timing is 12 degrees BTDC on a 79' 460.
Also, I know this sounds stupid but, check your plug wires and make sure they're all on the right cylinders. Just a thought...
Hope this helps.
Jim
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From: The Big, Oregon
I have had carbs with bad accelerator pumps pop through the intake when you step on it. Without the pump, opening the throttle causes a momentary extremely lean condition, and the cylinder will pop through the intake.
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From: Enid, OK
I took my truck for a drive last weekend. I worked the accelerator pump manually a few times and it seemed to help some. I still have the hesitation right off idle though. I will check the timing next.
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