Wonky Crankset- Help needed!

My single speed chainring/chainset does not go round in a round motion. It has a wobble and also makes a clunk under pressure. When I pedal backwards there is a distinct section of the cog which tightens the chain and resists turning. Any ideas what this could possibly be?

I have taken the chainring of the crankset and checked that it is flat and it would appear so. Maybe very minimally not flat. I have also tried different bottom brackets and the same thing happens...help would be much appreciated and thought the experts on here might know what is happening. I wouldn't mind an excuse to buy a new crankset!

Try any of the following....

Loose crank
Loose chain-ring bolts
Loose bottom bracket

Or have you had a tumble recently? Could also be a misaligned rear wheel or bent chainring

Is it a bio pace chainring? they are not round, but elliptical.

Or chainring is very slightly out. Loosen all chain ring bolts at same time then rotate, work fine now? Then tighten each one progressively whilst turning to ensure its centered, then fully tighten each.

some road chainrings / spiders are not that circular even after using the above centering technique - they don't need to be dead on as hey are used with a chin tensioner (rear mech)

From Sheldon Brown:

Chain Tension

The chain tension on a fixed gear is quite critical, and is regulated by moving the rear axle back and forth in the fork ends. If the chain is too tight, the drive train will bind, perhaps only at one angle of the pedals (chainwheels are not usually perfectly concentric). It should be tight as it can be without binding. If the chain is too loose, it can fall off, which is quite dangerous on a fixed gear.
Set the rear axle so that the chain pulls taut at the tightest part of the cranks' rotation. One at a time, loosen up each of the stack bolts, and tighten it back just finger tight. Spin the crank slowly and watch for the chain to get to its tightest point. Strike the taut chain lightly with a convenient tool to make the chain ring move a bit on its spider. Then rotate the crank some more, finding the new tightest spot, and repeat as necessary.

This takes a little bit of your hands learning how hard to hit the chain, and how loose to set the stack bolts, but it is really quite easy to learn.

Tighten up the stack bolts a bit and re-check. Tighten the stack bolts in a regular pattern, like the lug nuts on a car wheel. My standard pattern is to start by tightening the bolt opposite the crank, then move clockwise 2 bolts (144 degrees), tighten that one, clockwise 2 more, and so on. Never tighten two neighboring bolts in a row. You may prefer to go counterclockwise, but try to get in the habit of always starting at the same place and always going the same way. This reduces the chances of accidentally missing a bolt.

Once you have the chainrings centered and secured, adjust the position of the rear axle to make the chain as nearly tight as possible without binding. Notice how freely the drive train turns when the chain is too loose. That is how freely it should turn when you are done, but with as little chain droop as possible.