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:
|