Date:         Wed, 26 Jun 96 18:46:00 DST
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Easton Trevor <TEASTON@dqc2.dofasco.ca>
Subject:      RE: 73 bus / timing question...The good old days


Back in the good old days, (so I've read) before timing lights, scopes and 
electronic gizmos, the method used to set timing was to test run over a 
section of road with a couple of handy marks about 1/4 mile apart. Approach 
first mark at 30 mph in top gear, floor it, measure time to next mark. 
Advance timing a little,  repeat test, advance again and repeat until time 
decreases. Go back to last setting.

If your sure that its not knocking even when you floor it at low revs and 
the temperature is normal then there should be no problem with advanced 
ignition timing.

The object of advance as the revs increase is to enable the flame front of 
the exploding mixture to meet the piston as it passes top dead centre. As 
the conditions within the cylinder change (Throttle opening, effective 
charge volume, mixture etc) so the amount of advance required varies and the 
distributor centrifugal and vacuum advance mechanisms attempt to provide the 
optimum condition. This of course varies for every motor and so the factory 
setting is at best a good compromise.

Knocking occurs when the compression provided by the piston and the 
compression due to the expanding flame front raise the pressure and 
temperature of the unburned mixture to the point of spontaneous explosion. 
This  can be aggravated by glowing spots of carbon in the combustion 
chamber. The octane rating of the fuel, valve clearances , valve timing and 
exhaust system backpressures also affects the point at which the temperature 
and pressure cause it to ignite and hence the permissable advance.

|From: Gregor Durstewitz

|  While adjusting the timing the other day I made a discovery I want to 
toss
|out to y'all: It's an 1800cc\twin carbs engine, stock everything. Timing
|according to manual is 10 deg. ATDC. That's the way I had it set until now.
|I noticed though that it idles faster if I advance the timing a bit. So 
just
|for the fun of it, I set the timing to 0 deg., and took it for a testdrive.
|WHAT I NOTICED WAS THAT IT HAD A LOT MORE POWER THAT WAY. And I didn't
|notice any knocking or overheating (I do have an oil temp gauge). To make a
|short story long: I got scared I might screw up something anyways, and set
|the timing back to factory specs at 10 deg. ATDC. So my question to the
|list: