David,
Thanks for checking.
So I guess I want to keep the hole as close to the top (90 degrees from the
throttle shaft) as possible. Drilling this hole is making kind of nervous,
since
you have to drill from the outside blind, and you never know where you'll 'poke
through' until it's done. I guess I have to do some very careful measuring and
double check it before I drill.
BTW - how large should the hole be??
Thanks again, this has been a tremendous help.
- Bryan
>X-Unix-From: davidr@sunset.net Tue Aug 3 22:02:31 1999
>To: "Bryan Vandiver" <Bryan.Vandiver@eng.sun.com>
>Cc: "Spridget Mail List" <spridgets@autox.team.net>
>Subject: Re: Timing the 1275 ? (vac. advance with a sidedraft)
>X-Priority: 3
>X-MSMail-Priority: Normal
>X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2314.1300
>
>Bryan:
>
>Just went out and took a good look at exactly where I drilled the hole. It
>took me two tries to get it right. The spot is at 11:00 on the front
>throat, and goes through the bore only a few thousanths in front of the
>butterfly. Too far away from the butterfly and there won't be enough vacuum
>to opperate the advance. The choke (enrichment hole) is a few thousanths
>after the butterfly and would be subject to vacuum at all times. If I
>understand vacuum advance correctly, it's purpose is to improve fuel economy
>under light load only, like at highway cruising speeds. At Idle, an engine
>has to have minimal advance to prevent backfiring and hard starting.
>Centrifugal advance corrects the timing necessary as engine RPM increases,
>and Vacuum advance allows the timing to advance or retard based on engine
>load (how am I doing so far?) On a race engine, you would be under load
>most of the time, so vacuum advance wouldn't be necessary (hence Cooper
>Distributors with no vacuum advance provision). Manifold vacuum will not
>work correctly because manifold vacuum is too high at idle and under
>acelleration, resulting in timing that would be too far advanced in both
>those situations.
>
>That is how I understand it, anyway. My fuel economy improved about 4 mpg
>highway when I hooked up the vacuum advance.
>
>David Riker
>74 Midget
>63 Falcon
>
>----- Original Message -----
>From: Bryan Vandiver <Bryan.Vandiver@eng.sun.com>
>To: <Bryan.Vandiver@eng.sun.com>; <dwramsey@worldnet.att.net>;
><davidr@sunset.net>
>Cc: <spridgets@autox.team.net>
>Sent: Tuesday, August 03, 1999 3:00 PM
>Subject: Re: Timing the 1275 ? (vac. advance with a sidedraft)
>
>
>> David,
>>
>> Thanks! This is specifically the information I was looking for.
>Unfortunately
>> your picture didn't come out (I'm on a Sun workstation), but I have a
>pretty
>> good idea of where I should tap a vacuum hole. Since the dellorto, and
>weber
>> DCOE are virtually identical, your instructions should apply to my setup.
>I just
>> want to make sure that I know exactly where the hole should be placed...
>> With the plate fully closed, should it be right up against the plate (on
>the
>> filter side), or out from it a few millimeters, or is it that critical??
>For
>> this to work properly, I am under the impression that you want to have
>'minimum
>> 'vacuum when the throttle plate is fully closed, and have the vacuum
>increase
>> the moment the throttle starts to open. There is a hole where the 'choke'
>lets
>> in fuel, and I'm wondering if I can tap into that( since the choke never
>gets
>> used anyway),but I need to double check to see if that is in front or
>behind the
>> throttle plate. Does that sound like a possibility??, or do you think I'm
>better
>> off just drilling a new hole in the side of the throttle body?
>>
>> Regards,
>> Bryan
>> >
>
>
>
|