suddenly, no power at low RPM

Any ideas what might cause a suddenly non-responsive throttle (and low power) at low RPMs? I was tinkering around with the car this weekend, but nothing with the carbs or ignition. Very strange. Maybe a fouled plug that randomly happened. thanks for any tips. Jeff

Jeff,

If you’ve got Stromberg carbs, could it be an air valve (piston) stuck ‘open’ or not dropping all the way back to the bottom ?

PPN