Just went through this with an 800 eddy. If the car has a bigger cam and poor vac at idle you will get a stumble. First step is a recalibration kit. Get a vac reading at idle. Change the metering rod springs to the color coded set that meets your vac level. If cam is real big and real low vac bump up the initial timing to 18 to 22 degree's and recurve your dist. Mine also ran pretty good with an 850 holley DP. Holley does nopt use vac in the idle circut. Eddy does. Once i cured the stumble i found the eddy was much nicer on a street car then the holley and doesn';t leak fuel every where.;