75 vette,turnsover, has spark, gas down carb, won't fire or even back fire tried moving distributer

Is the spark plug black with soot?A black sooty plug will not fire most of the time.

Check for loss of spark first.

If the Cart sat for months, I would bet the ethanol gas gummed up your carb. Ethanol gas.... What are our politicians thinking????

Backfire indicates a timing issue. The timing chain keeps the valves closed when ignition fires. When the chain gets loose, it can jump one or more teeth on the sprocket and cause this problem.

firing order 153624 make sure valves on no1 cylinder are closed with cams pointing upwards then the rotor arm points to this plug lead and away you go ,This cylinder is no1 and then swop the others to follow the firing order ,once running either check with a timing light or swing distributor till engine runs faster then back it up a bit till it just starts to slow and should be right if it pinks the back it back a bit more till it stops pinking

ok, turning over and cranking are the same thing, what your saying is it won't fire, so , 2 things make a motor fire, electric and fuel, so starting with the easiest remedy , remove the distributor cap, and inspect the rotor and connection points that are inside the cap, check for any debris built up , sometimes you can clean them good enough to get the car to fire up, if it does , normally you would replace them , ( not that expensive) remove the number one cylinder spark plug, and once out put the spark plug wire back on it, ( your going to need help with this step) with insulated pliers , hold the plug and place the bottom of the plug against a grounding point (any bolt on the motor will do,, but try and keep it away from the carb as its Hopefully going to spark) have someone try and turn the car over as if to start it, look for spark at the end of the plug, if you have spark,, replace the plug and try and start the car , if it won't,, move onto the fuel problem, you need to make sure that the car is getting fuel, remove the fuel line to the carb turn the key for a second, you should see fuel splashing out, if yes ,, you should be able to start the car , if no,, check the fuel filter first , then the fuel pump,

fuel filter is going- will be ok at idle-when you tested it- but fails under load

check timming check for spark at distr if all esle check dist cap then

usually timing just loosen your distributer ,the thing wth all your spark plug wires going to it and turn slightly and keep testing your truck until you get it where you want it. after each slight move of half inch or so tighten it back up and fire the truck up to see if it dies.the distributer has a shaft on it and you will see like a half inch bolt to loosen on the intake manifold so yo can turn it

The ignition module inside the distributor may be the problem. Get a new one and try it out. The modules from GM are more dependable than aftermarket ones. If that is not the problem, it's nice to have a spare module in case of an emergency failure.
Squido