The throwout bearing in your clutch is the likely culprit here. Your clutch may be shot in addition, but you are probably looking at a costly fix here.
You need to use the clutch and the shifter smoothly together!
The simplest thing to check would be the universal joints on your drive shaft. See if you have any play in any of those universals. The springs in the center of the clutch disk could also be out and cause a clunking. MGB's also have thrust washers in the differential that wear out and cause a clunk in the differential.
You're a clunk-head...
The clunk is probably a universal going bad, and the popping out is probably caused by worn sifter bushings
The universal joint(s) on the driveshaft are bad.
Could be a number of things. I would check the U joins first then the motor mounts. Could also be the clutch plate (might have faulty springs that help to make it engage smoothly and absorb shock from releasing the pedal to quickly). Could be too much slop in the gears. Excessive wear in the gears and universal joints causes them to be loose and can make a clunk when they slap against eachother. Is the lever going into the transmission striking against something in the engine compartment? Maybe something has come loose and is being struck. Don't want to break a critical component. A broken motor mount will let the engine raise up and then slam down as the load on the engine is changed. (I had this happen in a '66 Caprice... or was it my '73 Fury?) All good answers,I'd check front u-joint first..my 2 cents answer all good answers, but before you dive into clutch or gearbox, check for slop on pinion shaft in differential also try letting clutch out slower
Vrrrrrrroommm If the driver puts his foot down. Brrrr-clunk-rrrrr-clunk-rrrrrrrrr With added gear changes.
A centipede with a wooden leg
It shouldn't ...
If the clunk is most noticeable at takeoff or when coming to a stop, the u-joints on the drive shaft probably need to be replaced.
Harley transmissions are known for the loud clunk. Make sure the primary/clutch oil level is OK. Or go ahead and change it out. You will need 24-26oz of sports trans fluid. There is a small pipe plug in the bottom of the primary case, not the one with the hex nut on it. Loosen and drain all the fluid into a container(discard old oil) Clean the magnet on the pipe plug. (there will be metal shavings on the magnet/thats OK) Replace the pipe plug, do not tighten all the way in, the thread is tapered. On the side of the case there is a small round fill plug with two screws holding it in place. (About the size of a silver dollar) Replace 24-26oz of sports trans fluid. That should solve your shift problems. To adjust the clutch cable. To have the clutch release where you feel the most comfortable. There is an adjustment barrel assembly in the cable housing attached to the front of the frame. Roll the rubber boot cover away from the adjuster. There you will find a hex body and locknut. Loosen the locknut,(1/2" & 9/16" wrenches) to have the clutch grab sooner: turn the hex body counter clock a few threads,(this lengthens the cable cover) test setting. To have the clutch engage at a farther out lever position, turn the body clock wise. The Harley-Davidson V-twin is a noisy engine. A whole bunch of nasty noise, like it is going to fly apart. Hope you have many years of good riding...
You may have U-Joint problems