fire out exhaust?

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kelseydum

Well-known member
Joined
Jul 9, 2007
Messages
860
Location
Little Rock, AR
Got my new 350 in the rod finally (it's a 1973 350 rebuilt stock). It's running really good, but for some reason am getting a shot of fire coming out of the exhaust. This only happens when it's at idle in park or neutral and I hit the throttle hard. I did notice it happen the other night on the freeway… I got her up to about 90mph and when I let off a small flame came out.

Is this due to incorrect timing, maybe carb running rich… or someone mentioned re-adjusting the valves after the motor was broke in??? What do you think?
 
usually its backdraft. real rich. all the air is burnt but not all the fuel is consumed and its temp is above its flash point so its still superheated and when it hits the air its ignites.
 
Just due to the unburnt fuel in the exhaust. If you seen it from inside the car then you must be runnin short exhaust :)
Might be a hair rich too

Jim
 
That is kinda normal when you are running wide open and then get out of it. I had the same thing and popping when I ran my car at the BP drags. When I got to the finish line and laid off the gas it was popping and flames coming out of my headers. I guess all the fuel that was going into the motor wasn't needed any more so it just burned off in the pipes.

Sometimes when I am driving around at night with open headers I can see fire occasionally come out of the headers too when I slow down.

Don
 
its not on fire in the pipes. only at the exit when it hits oxygen. you dont usually see it on pipes at the back of the car because it cools off below the flash point by the time it gets to the exit.
 
Thanks for all the replies. I'm using a worn out Quadrajet I'm almost positive has vacuum leaks, so I picked up a new Edelbrock 600cfm I'll put on there. Also my exhaust comes straight up out of the hood (if it had a hood) like the old derby trucks and they are about 2 1/2 feet tall... basically tight fit headers flipped upside down with glasspacks connected to them. It didn't do this with the other motor but it did have vacuum leaks from that same quadrajet.

Anyway, thanks for the replies and I'll see if this new carb helps.
 
Chandler answered your question. It's not the carb. It's cold oxygen getting sucked back into the pipe when you let off and it ignites the unburned fuel and the oxygen hits its flash point. A carb will not fix this. It's the pipes being short. We run open headers on all our dirt modifieds and they do this all the time. With a short exhaust, which you have, it is completly normal. You are going to be throwing good money away for nothing.
 

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