my carb is a stock 4 barrel quad on a oem 350 intake plugs continue to foul out,intake was modifide so bolts can go down center timing set by ear,now the motor shakes real real bad and wont idle at all and new plugs new wires,same thing. could my intake be the culprit or carb? or should i set my timing professionally thanks in advance for any help with the 350

 

I'd guess your timing.

 

It could also be a vaccum leak.

 

A vacuum leak, though engine timing plays a massive role.. i would get a timing light and adjust the fuel mixture....

 

check your 02 sensor as well