I think that bad rep is all hear say.
No it's not mate, I've got two stuffed F2 heads here, one appears to have dropped a valve and a guide, and the other one's valve guides are so loose in the head you can move them with your hand, I've never seen a K head like that, ever!
It's not just the valve guide material though, it's a combination of that, plus the actual valve angle was steepened in the F2/F3, the exhaust valves were too big and so it doesn't flow as well as a K head.
The cam design was poor which resulted in too much high speed stress on the cam chain, which caused the premature death of the cam chain, cam and rockers, rocker shafts etc, and the hardening on the valves themselves was suspect, causing "mushrooming" of the tops of valve stems.
All in all, a botched design. The best thing that can be done is to replace the head, barrels and pistons with "K" items, and then it's as "bullet proof" as a "K", or an F/F1.
Mosquitoes? The one's here are as big as Emu's!
