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Author Topic:   exhaust detonation
restore1
Member
posted June 21, 2003 10:55 PM
What would cause the exhaust to backfire and flames shoot out? It happens after you run up the RPM and let off. We just built this motor. 350 with 305 ported heads(601 casting), Comp Cam kit with 480 lift, Holley 600 carb ( we've tried different jet sizes 68,70,72 ) , stock distributor and coil with racing weights and heavy springs timed at 34 degrees full advanced. I've tried both a hot plug and a cold plug.
Thanks for any help, this one has us stumped and not racing tonight.


HRT187
Member
posted June 22, 2003 01:37 AM
Roll out of the throttle more. If you dump the gas it'll go boom-pop-boom


rico 08
Member
posted June 22, 2003 11:16 AM
Might be sucking air somewhere,check the headder gaskets etc.


restore1
Member
posted June 22, 2003 11:50 AM
We thought it could be a header gasket, but would'nt you be able to hear a header gasket leaking?
What kind of symptoms would you have if a intake gasket was leaking internally?
Thanks for any help guys.


Darren Scott
Member
posted July 02, 2003 05:48 AM
Sounds to me like a header gasket or a cracked header leaking air into a fuel-rich exhaust gas mix...boom. If it was an intake gasket leaking internally, you'd have a lot of oil smoke to tell you.


skinny
Member
posted July 03, 2003 02:44 PM
i lost the boom pop boom on mine by switching to a non locked distributor and giving it a little more timing, with the loose dist. i can still start up. Actually running about 39 degrees


dilbert
Member
posted July 12, 2003 11:10 AM
I too have this problem on basically a stock set up. Doesn't seem to hurt performance--just a little un-nerving. Have switched carb and replaced dist. cap and rotor--still pops. I am thinking vaccuum leak(cracked intake?) or bad rings or valves. Would either of these cause the symptoms restore1 talked about?


racer17j
Member
posted July 12, 2003 11:55 PM
if your to rich it could cause that also i know in our old cruiser car we had to run on 7 cylenders and every time we let off all that unburnt fuel in the pipes would give us a boom after they got hot


dilbert
Member
posted July 13, 2003 01:20 PM
I think I found mine! The rough track last night causee my manifold extension pipe to fall off! It must have been loose allowing air to enter the exhaust! I'll find out if this was it next weekend!


howie605
Member
posted July 13, 2003 10:30 PM
Had the pop bang boom going on with my car also....changed carb, messed around with timing/distributer and it all ended up being a bad battery. Check your battery and make sure you have a full charge!!!


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