I’ve got an HP4 on PX200, there are two woodruff key channels. Is one intended for the old PK timing ?

Is the flywheel compatable for both large and smallframe engines as I’ve noticed two different versions for sale ???

So if I fit pkxl crank and stator to s/f casings will I need a separafe HP4 ?

The HP4 flywheel is originally from a s/f. If you change to pkxl crank and stator the flywheel fits straight on, But depending on the state of tune that your s/f is you can cheaply convert to the hp4 by drilling out the rivets on the original flywheel boss and using countersunk 6mm allen screws ( tensile 10.9 or 12.9) replace the boss on the HP4. This works well with a full-on Malossi 135 reed motor. You can use also by taking an Early T5 centre boss out and fitting to an HP4 or working the other way take a non xl type electronic smallframe flywheel and fit a px or t5 boss to it. I have found the best to use is a pk100 electric start type flywheel and remove the starter ring, presto lightened s/f flywheel on px malossi. Do it careful and no failiures since 1985 and thousands of miles.