861 Ford pops back through carb beginning at about 1000rpm through 2300rpm. Have done complete tuneup(cap,rotor,wires,points,condenser,plugs), carb rebuild, compression 140psi, valve job(new valves,springs,guides,surface). Pull #1 plug wire pop stops and resumes when put back in place and does not pop on 2,3 or 4. Distributor cam lobes are not worn, new distributor bushing. Adjusted valves loose and tight, set hot @.015. Timing-4 degrees @ 450rpm, 26 degrees advance @ 2000rpm. Cam gear and crank gear timing marks correct. Camshaft lobes measure the same(mesuring from retainer to top of head) as cylinders 2,3 and 4. Intake has no leaks or cracks and surface is flat(tried copper silicone to seal). Has Zenith carb tag 13875A. Air cleaner has been cleaned. Have tried with and without the fuel tank. Engine runs no different than when started. Idles great and runs good up 1000rpm and then starts to pop. Any ideas?? A friend bought the thing running like this so do not about how it ran before. Thanks for any help.