I've just done them on my 300. It involved getting the line on the powervalve pulley to point at the little dot punched into the side of the barrel when the valves are in the high position by twiddling the adjuster nuts. Then you've gotta plug the TPS in so the valves go to the low position and then unplug it again to make sure that when the valves go back to high, the line is still pointing at the dot! All the while listen out for the sound of the servo motor straining and immediately kill the ignition if it does! You must slacken the tension on the lower cylinders cables if it does strain. There's a long black adjuster nut that does this job.

I don't know if this is the same as the 250 method but i hope it helps all the same.
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