Week spark the spark on the plugs is very weak

low compression can be either leaking head gasket-bad head /burnt valves--piston rings --damaged cylinder wall all of these are a tear apart fix a rebuild depending on mileage and condition of engine a replacement engine might be a better financial solution ---as for weak spark coil --wires-spark plug -fouled spark plug --and if same cylinder as damaged one the compression

Most probably u have a spark plug coil gone bad or a spark plug wires.
But if not then then go through the following:-

1. Check fuel filter or clean system
2. Faulty or incorrectly gaped spark plugs
3. Defective spark plug wires .
4. Emissions system components faulty.
5. Low or uneven cylinder compression pressures.
6. Check as described in
7. Weak or faulty ignition coil(s).
8. Weak or faulty ignition system.
9. Vacuum leaks at intake manifold or vacuum hoses .
10. Dirty or clogged fuel injector(s). .
11. Leaky EGR valve.
12. Fuel injection or engine control systems malfunction.

I know it is along list but going through them will make a peace of mind to know which area is week and which is faulty.
Hope this Helps.

Something else wrong with that cylinder. Check compression and swap injectors, etc.

Engine will not run with no spark or a weak spark. Continuity test will only reveal that the winding is not open, not if you are producing a weak spark that will not jump the spark plug gap.

check pulse generator circuit for any opens or shorts..even if you still show a weak purplish/red spark its bad..it must be a big bluish/white spark..check plug #1 for spark and then check #3 foe spark if there both week then its your pulse generators that are bad ..but if one of them has a blushish spark then it that systems coil..eg #1and#4 or the #2and #3 coils..

Change the spark plugs,they are worn out.

it sounds like the engine is cooking up the plug,, if a new plug gets you started again once you have fitted it, its not the bike's spark,,,its the old plug,, its burnt out,i think the carb is running vey week,, and this makes the engine run very hot,,,it could melt a piston crown !!! have you tinkerd with the exhaust pipe in any way? as this will throw the card way out of tune,,,and they sound very noise too, if you try a hotter plug in the bike it should sort out this sparking problem,,,mine eat plugs at a set a week,,,i had the wrong pipes fitted to my bike when i got it,,,

Replace the plug with new, non champion if possible, That is what I would do first.