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Backfire in the Carb

PaulQ

By PaulQ
in Ask A GM Technician

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PaulQ Enthusiast

PaulQ

Posted
Posted

First off not sure if I should be in this forum or Performance but I've been posting in both trying to find an answer.

 

Here goes,

 

94 fullsize Blazer 350 with Vortec heads and Vortec intake(Existing TBI), in the process I put on new roller rockers, pushrods, and lifters along with a new crane cam(Duration 254/ 264, Lift .401/ .423). Also put on new headers.

 

I finally got some codes and here's what they said or at least how I interpereted them(EGR, MAP Sensor, fuel pump relay, and electric spark timing or ignition module).

 

The EGR is brand new so I replaced the MAP Sensor, haven't gotten around to the fuel relay( don't think it's related to this problem, although I could be wrong, and the EST/Ignition mod. I believe is from setting the timing{Not sure about this})

 

In park, neutral, and idle everything is perfect I can rev and hold at any RPM with no backfire. Under load it's a different story. I don't notice the backfire at lower speeds or higher speeds, just seems to happen when I get on it good around third gear I would guess. The idle is still fluctuating just not as bad. Currently have it timed at 5* advanced. That seems to be the best happy medium at the moment.

 

Also blowing water or moisture out the exhaust at startup( which would lead me to believe the valves) just not sure how much more I could adjust them. Adjust when running( back off rocker until it clatters tighten 1/4-1/2 after clatter stops. I've tried both 1/4 and 1/2 turns and neither seems to make a difference.

 

Sorry to keep throwing up these long posts just trying to get resolved. Thanks to everyone past and present for taking the time to assist me in my time of need.

 

Hope I didn't leave out any important info.

 

Paul

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