What causes an engine to 'buck' at low speeds?

[RICK LAKE]

Flygirl Natalie It's not a single thing. Starting with tune up, Fouled plugs could cause this at idle with a carb running rich or lean.
Weight of flywheel Depending on size of motor(cubes) and camshaft with LSA number this could all cause lugging of the drive train, or hickps. A larger flywheel stores more energy that a lite one. this helps stop the pulsation of each cylinder being fired at low rpms.
Gearing in the trans and rearend also can cause lugging of the car. The lower the rearend gear the wider the trans gears need to be to not have the motor running at 600 rpms. Unless you have a large camshaft with 110 LSA and choppy idle the lugging should be minimal. I have a 482 with 22 pound flywheel and FI system. Both trannies have a 3.00 or higher first gear. With a 3.31 rearend I can idle drive the car without the lugging like a parade speed. If you step on the throttle it will delay for a second because of the fuel dump and air change into the motor. The best thing to do is not let the car drive at idle speed, 1000 rpms with large camshaft and 800 rpms with a small street camshaft. If you can't run in these rpms, change the rearend ratio or trans mission first gear ratio. I can say the any gear higher than a 3.00 in a cobra is a waste of time unless you are running a gearing under 3.00 in the rearend. Lugging a car can also due damage to bearings on the crank and rods by pounding them, low oil pressure to the upper end of the motor, damage to the drivetrain on the rearend backlash of gears, same for inside a trans, a solid hub clutch has no springs to absorb the pulses from the motor at idle speed. As said it's a combo of things. Rick L. Ps missed the call.