Exhaust Backfire During Startup

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Jun 30, 2014 | 05:18 PM

nelsontj

Thread Starter

Registered User

Joined: Feb 2009

Posts: 139

Exhaust Backfire During Startup

On my 1970 442, w/455, I get an occassional exhaust backfire when I am starting the car up. The car has original engine with no modifications. I do have Flowmaster Series 40 mufflers on it. Any ideas what would cause this?

Jun 30, 2014 | 05:44 PM

oldcutlass

Administrator

Joined: Oct 2009

Posts: 42,496

From: Poteau, Ok

Excess unburnt fuel in the exhaust system and/or an exhaust valve not closing all the way.

Jun 30, 2014 | 09:45 PM

TripDeuces

Registered User

Joined: Jun 2010

Posts: 3,613

From: Rogues Island, USA

Severely retarded timing, excess fuel in exhaust system (too rich or someone pumping the poo out of the throttle), sticking valve.

My three guesses

Jul 1, 2014 | 06:16 PM

Railguy

Registered User

Joined: Mar 2010

Posts: 1,309

From: South-central Pa.

Quote:

Originally Posted by TripDeuces

Severely retarded timing, excess fuel in exhaust system (too rich or someone pumping the poo out of the throttle), sticking valve.

My three guesses

Burnt valve?Fuel leaking into intake while shut off?Does it only do it when cold?That is to say if you shut it off the start it back up will it do it?
railguy