Thanx Mark ;
? Did it hole the piston or do the usual fry the edge of the piston crown down into the top ring land ? .
Yes, air cooled engines need higher octane but also they need really sharp timing, few are designed to have more than 29 ~ 30 DBTDC at full advance and as the timer wears it tends to advance a bit more, often too much if you use the base timing mark....
This is why I love and use my 50 year old Craftsman inductive dynamic timing light with the advance dial on the back ~ it allows me to set the ignition timing *exactly* where I want it under actual road RPM .
It also allows easy testing of advance curves and rates of advance and return, it's not uncommon to have slow return of timing advance..
I wish I could go to TEXAS, I love it there .
Looks like I may be driving up to the S.F. Bay area soon for free old Honda Moto parts =8-) .
-Nate
LIVE in the world as it is, WORK to make the world as it should be
MARK wrote:
I'm not really sure why that piston melted. It's the first time I've ever had this happen. I bought this bike (and it's 1970 twin) from the dealer salvage/donation auction some 15-years ago. It was reading 12,000 on the clock. I'm not sure if it was already compromised from before I bought it, or what. It DID occur on an especially hot day here, and after I'd been pushing it pretty hard.
I always run high octane in the the bikes, especially on hot days, even at this altitude (where the thinner atmosphere equates to an effectively lower compression pressure). Below 40 degrees F, 87 octane is OK.
My high school shop teacher preached that all air-cooled vehicles should run premium. In addition to a CB750 (with HondaMatic!), he also had a Corvair.
Mark (currently in Port Aransas, TX, where the cool, wet weather from Beta is welcomed after a hot, dry Mile High summer...!)
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Posted by: Nate <vwnate1@yahoo.com>
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