Great explanation MarkT makes since now 

Blimey, great explanation by Mark, & stories coming through. Enjoy reading them all. Should start a Post--How i blew my motor!!. Mind you sometimes they blow with no cause found. Like the liner broke off below the inlet on my 100 bucket racer & did the piston break first & cause the liner break, or did liner brake first. When examined there wasn't much holding the liner as the inlet was carved out huge. Think i've still got that cylinder--i'll get a pic sometime.

WOW - very interesting Mark, I was not aware of all the reasons and angles, thanks!

Honda made some really cool stuff.  My most "expensive car" back in 1984 was a little honda Civic with CVCC technology designed to run super clean before electronic fuel injection solved many things that manufacturers tried do do the hard way!  This engine had a complicated little 3 barrel carb (which I remember rebuilding curbside in a snow bank) with a tiny barrel that fed a tiny intake valve that was designed to light a very lean main mixture coming in through the "regular" size valves to meet EPA goals.  It was very "analog" with sensors, and hoses and valves and switches and crap all over the place, but this little car had a 5 speed, got 50 MPH and was incredibly fun to drive!

Here's a 20 year old Honda Hybrid Car i'd not seen before. Bit off subject i guess.
www.trademe.co.nz/a/motors/cars/honda/in...t/listing/3400176809

Here's the update on the situation:  yamaha-enduros.com/index.php/forums/gene...8-dt1-runaway-update