mann1977, I recently pulled the valve cover off of a friends 250 for the same reason, it ran terribly at all RPM ranges, had lost power and had 0 compression on the #1 cyl. The culpret? Just as as Twisted6 said, the intake rocker on the #1 cyl. had for some reason worked itself loose. We pulled the head, checked the valve, push rod, head gasket, etc but never found what caused the problem. We re-seated the valves and bolted her back up. That was about three months ago, still running like a top. The old advice guy at NAPA said that the rocker arm nuts on 250's were bad for backing off? I don't know if that's true or not, but I still don't know what caused that nut to back off. My buddy swears that it was a new nut when he had the motor rebuilt about 7,000 miles ago.
