Engine starts but One cylinder is not firing and what should I do to fix this problem?

SOURCE: engine wont fire up

Do you have fresh gas in the bike? Try changing the plugs with new ones and check for spark. You can do this by putting the new plugs on the plug wire and grounding it to the head on the engine crank the motor over you should see a bright blue spark. Check one plug at a time. No spark check the ignition wires and coils. As for the oily plugs it could be they are just fouled caused by either flooding the motor while trying to start, bad plugs, week coils, bad gas, poorly adjusted carb's. I would start with the plugs and work my way back to the carbs. Still fouling the plugs after all that start checking the engine, ie compression check ect.

SOURCE: my '86 suzuki savage won't rev up it just back fires

When I had my savage it backfired all the time. They are known for this. Make sure you fuel is not to lean. Just adjust the fuel. You should adjust that and put some sea foam in it or ethenol treatment since most of the gas is terrible these days. Running 91 octane will help. Also you will want to replace the muffler gasket too.
When you replace that it will smoke which is normal.
I sold mine but I know the bike pretty well from tearing it apart due to trying to fix it from not running properly. Let me know if you have any more issues.

SOURCE: SPARK PLUG GAP FOR A 3cyl.suzuki,660cc,12valve engine

From a factory service manual >

Could you take a moment and rate my answer? Thanks!

SOURCE: suzuki gn125 wont start. checked carb, cdi, coil.

Check the valve adjustment. If a valve is standing open just a little, the compression will be too low to start the engine. Check fuel delivery by dribbling a little gasoline into the carb and try starting the bike. If it starts and runs for a second or two, you're not getting fuel into the cylinders. Check you carb again.

SOURCE: suzuki m50 shift gears.

You may not have a problem at all!
There is a sensor on your kickstand! You can start the bike while its in neutral and have the kickstand down, but if its in a gear with the kickstand down, the bike will automatically turn off. Also, if the bike is in gear with the kickstand down, you will not be able to start it. This is a safety precaution.