PK backfire

[vespistazd]

Hello...i was wondering if someone can give me some advice...my PK is equipped with 133DR,Keihin PE24 (main jet 95, idle 48), original PK 12V ignition and flywheel, giannelli right hand exhaust and casings are just ported to match the cylinder and intake manifold(nothing too much)...i noticed in last few weeks that my PK backfires in low rpm(when i add a little bit of gas just so it revs up a bit for few times it backfiers strongly) i changed the other ignition also original from PK, bought new spark plug and it backfires again🙄🙄...at high revs it runs ok but sometimes at this low rpms it backfires and when i check the spark plug it is completly black...so i tried with idle jet 45 and did a little ride around town it still backfired but now the spark was a bit on the lighter side(leaner mixture)...now i ordered a brand new BGM pro CDI unit and will see how it runs with new CDI unit...but i just cant figure out what is going on???

[jbcollier]

Sheared flywheel woodruff key? What is the timing at.

[vespistazd]

Timing is on the original mark of PK50 and was running great for last 5000km...woodruff key and crankshaft are both new and working fine.

[vespistazd]

It fires when i release the throttle...bang and lot of smoke...

[jbcollier]

The factory marks are not precise enough for tuned engines. You need to use a piston stop, degree wheel and a strobe light to set the timing properly.

Have you double checked the flywheel hasn't slipped? Sure sounds like it.