Back fires through exhaust

[MoabCJ8]

Having an issue I cant seem to figure out. Jeep runs and drives perfect but if you rev up the motor and let off quick it will back fire through the exhaust. I have replaced the intake/exhaust manifold gasket thinking that was it but it made no difference.
I tried disconnecting the plugs one at a time to see if a certain cylinder was doing it and it did it not matter which one I disconnected.
It is a rebuilt 258 with the original Carter carb. Everything looks tight and perfect.

Possible things I have been thinking of:
-Carb adjustment
-Spark plug.
-Low octane fuel

Any ideas or first hand knowledge of this problem?

 

[mysunnshine]

I'd say an air leak in the exhaust or really short exhaust.

Sent from my SCH-I545

 

[skiptown]

Did this just start or have you "done" something to the engin recently

 

[MoabCJ8]

I'd say an air leak in the exhaust or really short exhaust.

Sent from my SCH-I545

The exhaust goes all the way back but I think the down pipe might be loose where it connects to the manifold.

 

[MoabCJ8]

I purchased the Jeep about a month or so ago and have been restoring/building it.
Haven't driven it more then a mile so far but this is one of its little quirks that are bugging me.

 

[Rosco1974]

Timing? What is it set @ and was it checked warm with vacuum advance blocked off?

 

[John N]

Yeah that.....check the timing.

 

[b.b.chev]

Does it still have the air pump hooked up ? When I was a car mechanic I used to run into bad diverter valves causing this problem .

 

[MoabCJ8]

Yes the it has all the original smog components.

Does it still have the air pump hooked up ? When I was a car mechanic I used to run into bad diverter valves causing this problem .

 

[MoabCJ8]

I tried messing with the timing and it had no affect on it.

Timing? What is it set @ and was it checked warm with vacuum advance blocked off?

 

[Kim Dawson]

Might do a compression check and make sure a valve stem isn't bent or something holding a valve open.

 

[MoabCJ8]

looks like b.b.chev is correct. I disconnected the pump and it stopped back firing.

Does it still have the air pump hooked up ? When I was a car mechanic I used to run into bad diverter valves causing this problem .

 

[b.b.chev]

Glad to hear it was an easy fix.