Originally Posted by Stormtrooper
Alright so i have a 350 engine, vortec heads, edelbrock intake, comp roller tip rockers, 650 edelbrock thunder series carb. Intial timing at 11 degrees.
Right now it idles terribly, backfires out the back some and wants to die if i dont let it warm up enough for driving. Also misfires at any engine speed(dash shaking) and im way down on power.
I replaced the cap, rotor, coil, control module and the plugs when the module went out a few weeks ago.
i adjusted the valves messed with the carb adjustments when misfire started and still nothing. also ran some seafoam through the tank and carb still nothing. iv been hella busy with work though so i dont know when exactly the problem started. The plugs were black so im thinking i might lean it out with a rod change but it has always run rich. even before the problem started just havent got around to getting new rods or springs for it.
any help is appreciated as this is very annoying
I need to understand when you say "backfire" followed by "out the back" I would read this as an afterfire out of the exhaust as opposed to a backfire out the intake (carb). The causes of each are mostly unique and the black plugs and rich running you observe would support rolling explosions out the exhaust. Lean on the other hand tends to be flaming, eye brow scorching explosions out the intake.
Different things can result in these symptoms as well for example a sparkplug that is too cold on the heat range scale will carbon up and cause the engine to run and act rich because of the miss or late fires that happen with this condition. Low compression will look like a rich condition for many of the same reasons as a carbon fouled sparkplug. If this is a Chevy one cannot rule out the cam and or lifters gone bad this will act much the same as the problems you're seeing. Late timing as well which could be ignition and or cam to crank. Certainly carb settings like too high a float level, too large a jet of too small of off calibration metering rod, too much fuel pump pressure can be contributors as well. A weak ignition from failing high voltage wires to the voltage going into the igniiton being too low such as running HEI with a 9 volt drop resistor made for a points ignition somewhere in the wiring to the distributor that wants a full 12 volts. Lets not forget choke adjustment and of course whether this has an air gap manifold. These are more things that can make an engine run rich or look as if it's rich.
A vacuum leak would add air which by definition would lean the mixture which would result in backfires through the intake or a lot worse. But here you'd be looking at hot, dry, white spark plug insulators unless the engine was so rich that it prevented the typical effects of an air leak into the intake system.
Something of shotgun approach to problem solving to be sure, but from here that's as good as it gets.