They were still crap Jim. I'd rather have those 10 Jawas, at least you'd be 1: able to get parts and 2: be confident of finishing a meeting.
The reason they're rare is that most of them ended up as boat anchors or like John Titman used his for, as a door stop. We've got a mate who thought he was going to clean up big time selling his and asked serious money for it in the speedway magazines in the UK. He got no response whatsoever other than blokes calling him a thief for asking so much. Jonesy's got one of the best speedway engine collections in the world and he didn't even bother with our other mates 4v JAP. Having said that, he doesn't have one in the collection and he's hot to trot on a swap when K2000X finds that the parts situation makes the engine financially unviable. I know I'd rather have a Jawa that is not only faster, lighter and way more reliable but you can buy parts in K Mart (well...not really but you know what I mean). JAP dohc4v engines were too little, too late when compared to the Weslake and even the not so good 894 twin cam Jawa.