Hey Hans, you stole MY Haynes.
Larry
-----Original Message-----
From: Hans Huber <hans@desmodromic.com>
To: spridgets@Autox.Team.Net <spridgets@Autox.Team.Net>
Date: 29 July, 1998 10:46 AM
Subject: Re: Timing the '72
>
>Chuck,
>
>Advancing past a certain point won't actually do any good.
>That point is called MBT (Mean Best Torque (unless my
>notoriously porous brain dropped something)), and anything
>beyond that will just increase your problems (as Jeff Z said)..
>
>Having said that, the '72 is a hard puppy to get to ping,
>since they lowered the compression to 8.0:0 (for the US)
>for emissions-related reasons (meaning I really don't know).
>My guess is that they wanted to increase the advance for
>more complete combustion..
>
>My technique is to leave the vacuum advance connected,
>and advance the timing until it sounds like too much (starts
>to stumble a little), the back it off a bit past the
>ideal (fastest smooth idle) point, then a touch more for
>safety. and listen carefully for knocking. This is a crude
>and indefensible method of setting the timing, but it's
>always worked for me (with apologies to H.S. Thompson, and
>real mechanics, and my mother (sorry, mom)).
>
>Looking at my trusty (and usually trustworthy) Haynes manual,
>I see that they indeed made the advance curve steeper for
>the emission control models (although I think there's a
>misprint here, as 2 advance levels (19 and 23 degrees) are
>labeled "2,300 to 2,500 rpm".
>
>In any case, it's difficult to figure out what they're saying
>here, but it looks to me like it wants more than 10 degrees
>at idle. Big news, that. Looks to me like it might want
>as much as 26 degrees at idle, depending on what the hell
>that "19' at 2,300 to 2,500" line is supposed to be. You
>might try timing it statically, and see how much (centrifugal)
>advance you're actually getting at idle. The centrifugal
>advance comes in at 500 RPM on emissions distributors.
>
>I'd never heard of a timing light with an advance dial, as
>Jeff Z. just described. Woo hoo! Gotta get me one of those!
>
>As Jeff said, the best way to set the timing (from a
>performance standpoint) is to set the correct total (full
>advance) timing, and Jeff's light sounds like the easiest way
>to do that (you can also guess and/or mark off the total advance
>on the timing cover, but that's a crude hack (cough)).
>However you do it, you should rev up the engine after
>setting the timing, and see that the timing mark moves to
>somewhere in the vicinity ofthe total advance figure
>
>It looks to me like your engine ('72 emissions) wants
>37 degrees total advance (7' static + 30' advance at ?? RPM)
>
>Enough nattering on. Good luck with it.
>
>-Hans "advanced *way* beyond MBT" Huber
>
>P.S. Does anybody have a newer revision of the Haynes
>manual that has the correct info on centrifugal advance
>for emissions dizzys? My Haynes is old enough to be missing
>the title page (and at least pages 111-116), and is nicely
>rebound with black duct tape, so I don't even know when it
>was printed.
>
>On Wed, 29 Jul 1998 08:24:19 EDT Chuck Ciaffone wrote:
>> It happens every time I tune my '72. I set the timing,
>> using a timing lite, to about 10 degrees advance with
>> the vacuum advance disconnected and plugged. It runs OK.
>> Then I start turning the dizzy for more advance, and it
>> runs better. SoI would guess that I probably run normally
>> with about 15 or so degrees of advance, AND it still
>> never seems to ping. Can/should I just keep advancing
>> the timing till it pings? What's probably going
>> on here?
>>
>> chuck
>> --
>> =====================================================
>>
>> chuck ciaffone chuckc@ibm.net
>
>
>
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