pull the petcock out of the tank and clean the filter off.
Then order the tool from treats to pull the Bosch flywheel off also get a new set of Bosch points and a condenser you will probably end up discovering that you have rust Pits on the cam lobe of the flywheel this will wear down the cam follower on the points there for the points will close up retarding the timing which works good for high RPM combine that with a weak condenser heating up and failing and you get your problem fuck the grammar you're just getting this information in one long sentence
Get some white grease for brakes lithium grease is what it is make sure you put a little fat on the cam lobe that makes the points open and make sure that if you have rust pitting and it's on part of the cam lobe that happens while the points are opening your flywheel is a paperweight and you will need a new one set the points at 16th AO and time it at about 18 degrees and you will be fine fuck you can 18 degrees is fine he's running a stock carb don't listen to Ken he's full of shit so you want your points to open 1.4 mm that's how far the pistol be from Top Dead Center you can just stick a piece of cigarette paper between the points and when you get to that point they should just slide out that'll put you read about 18 degrees you should also post a picture of this bike that you got somebody on here probably knows the history of it or what problems that had that the previous owner dumped it on you for chances are it's going to need crank seals and another thing that'll make the bike hard to run and start is too large of a spark plug gap you want to get that puppy down below 0.020" but not smaller than 0.019"
And when you pull the petcock out of the fuel tank the little plastic screen will unscrew or pull off when you have that removed you'll see a little tube sticking up in there that's for the reserved portion of the fuel tank I suggest cutting it in half and add a 30 degree angle the newer gas with alcohol in it has a different tension in the liquid and it creates a resistance to flow that is greater so make sure that your fuel line hasn't shrunk because if you do run out of fuel you'll find that you may have to actually blow into the gas tank to get the flow started once you have a connection of fuel with no air bubbles the fuel will flow find another thing that happens quite often is the fuel cap gets rest that tends to block the fuel cap the bike will run fine when you first take off but the outside of the tank cools off and creates a light vacuum within the tank then the fuel stops flowing in the bike quits running so you want to make sure that the fuel cap is vanting many folks will take and drill a small 16th hole through the side of the cap to the underside not to the top to be sure that it is venting properly I also suggest you get an air filter of some sort can will jump in here and tell you to get the blah blah blah metal screen filter yeah that's okay it works but anything on there that will stop the rocks and sand and bullshit that the chain and rear tire is going to be throwing into the carburetor because if that happens you're going to end up with score lines in your cylinder and low compression anyway be sure you post some pictures of the bullshit and I would also take a small stick and put a little rag on it with a zip tie over the end and rub it around the bottom of your tank and see how much rest and shit there actually is you may find that you're going to need to clean your fuel tank if you don't the rest will break loose and you will be doing the rinse and repeat bulshit of everything and replacing your fuel filter repeatedly that is if you actually have a fuel filter in line to the carburetor and a big indication that you have rust in the fuel system is the fact that the porcelain on your spark plug was Rusty that's not a good sign the other thing that could be causing this is water got into the engine because the dipshit had it out in the rain last so if you end up pulling your cylinder off and you notice that there is rust on the crankshaft itself then your bearings are pretty much fucked so you might as well just order a new crankshaft from treats get the stiffy whatever crank new bearings new seals and be sure to get a INA rod bearing for it because the one that comes with that crankshaft ain't the best.
And when you put the cylinder back on make sure that you slowly tighten the bolts in a Criss-Cross X fashion bring it up one pound at a time and stopping at 7 foot pounds if you go past that and stretch the studs well will just call you a dumbass so be prepared to get flamed here and there but I think I gave you enough information that you can do this without having to repeatedly wipe your ass so good luck get the shit you need get the thing running and maybe you'll have something Dependable to ride maybe you'll just be one of those poor SOB's they can't get the fucking cap back on the toothpaste tube I don't know what your skill-set is but good luck have fun