Big Boom!! Help
Thread Starter
Instructor
Joined: Jun 2004
Posts: 162
Likes: 1
From: Johnsburg IL
Backfire - Big Boom!! Please Help
Changed intake on my 69 and I must have firing order off because when I started the engine it backfired big time. The sound level was that of an M-80 going off in a trash can.
What do I need to check for damage? Is pulling pan enough or possibly heads to inspect pistons? I disconnected the distrib and turned motor over and don't hear anything but not conformtable to try and start without knowing whats the best way to approach.
Thanks to all for suggestions!!
What do I need to check for damage? Is pulling pan enough or possibly heads to inspect pistons? I disconnected the distrib and turned motor over and don't hear anything but not conformtable to try and start without knowing whats the best way to approach.
Thanks to all for suggestions!!
Last edited by colorado1967; Apr 19, 2005 at 12:08 AM.
Race Director
Joined: Nov 1999
Posts: 10,643
Likes: 8
From: Foxfield CO 1970 Convertible
I hate it when that happens. Did you have to change underwear? 
I doubt if anything in the engine was harmed since the intake is not a confined space. Don't forget, an explosion just like that is happening several times a second inside the cylinders. Don't bother with the pan. If it makes you feel better, give the intake a once over looking for cracks.
On the other hand, if you have a Holley carb, you may have blown out a power valve. You might check those, or you will be very running rich now.
If you didn't have the air cleaner on, that may have contributed to the flashback since the air cleaner is supposed to prevent this - make sure you have it on...
Double check your timing and get back out there to fire that bad boy up!
Good luck -
I doubt if anything in the engine was harmed since the intake is not a confined space. Don't forget, an explosion just like that is happening several times a second inside the cylinders. Don't bother with the pan. If it makes you feel better, give the intake a once over looking for cracks.
On the other hand, if you have a Holley carb, you may have blown out a power valve. You might check those, or you will be very running rich now.
If you didn't have the air cleaner on, that may have contributed to the flashback since the air cleaner is supposed to prevent this - make sure you have it on...
Double check your timing and get back out there to fire that bad boy up!
Good luck -
Melting Slicks
Joined: Dec 2004
Posts: 2,101
Likes: 3
From: Cruising somewhere in St. Louis, Missouri
I hate it when that happens. Did you have to change underwear?
Maybe it's the beer....but that was F'in funny...ROTFLMAO
lol
Maybe it's the beer....but that was F'in funny...ROTFLMAO
lol
Last edited by luerja; Apr 19, 2005 at 01:24 AM.
Instructor
Joined: Apr 2004
Posts: 166
Likes: 0
From: Troy MO
Might check your holley (if running one) my 67 GTO has ruined many power valves.... I have a big compression problem with it... (way too high) and often have back fires when My octane is too low.... and EVERY dog gone time I lose a power valve. its an easy fix though.
Good luck with it,
Loren
Thread Starter
Instructor
Joined: Jun 2004
Posts: 162
Likes: 1
From: Johnsburg IL
Thank you all for the feedback. I was afraid I could have cracked a piston or worse. Will check for gas / oil and get firing order correct. After looking at distributor cap again I see it had two marks. The one I'd marked for #1 and then another from who ever installed. I used theirs.
I also have the Roch carb so should be OK there. This is the # correct engine (L-46) and I would be very disappointed if I blew up.
Thanks!!
I also have the Roch carb so should be OK there. This is the # correct engine (L-46) and I would be very disappointed if I blew up.
Thanks!!
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Race Director
Joined: Nov 2000
Posts: 11,872
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From: Waterloo ontario Canada
Like the rest it won't do any damage to the engine, the power valve might even survive and you will know when the motor starts if it is running extremely rich.
When I start a motor like this for the first time I advance the distributor until the motor hesitates while turning over, this is too much advance so I just back it off a touch to start. If the motor really turns over fast it is retarted and can backfire. Better to be too advanced then retarted. So advance until the motor hestitates, back off a little and after running use a timing light.
When I start a motor like this for the first time I advance the distributor until the motor hesitates while turning over, this is too much advance so I just back it off a touch to start. If the motor really turns over fast it is retarted and can backfire. Better to be too advanced then retarted. So advance until the motor hestitates, back off a little and after running use a timing light.