Vacuum timing? - Team Camaro Tech
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post #1 of 3 (permalink) Old May 28th, 01, 08:41 PM Thread Starter
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Join Date: May 2001
Location: Lapeer, Michigan
Posts: 77

I recently upgraded my HEI on my 350 motor to a Proform HEI tune up kit from Jegs.
I have a holley 650 vac sec and edelbrock performer intake w/ sportsman II heads and flat top pistons. T350 trans w/B&M kit
My mech adv is 20 initial and 36 total.
with the vac plugged in it is 20 inital (no change) and 60 total.
it behaves fairly well. Somtimes it might feel like it skipps a clyinder or two every few seconds at light thorottle acceleration untill all the timing is in but i think that it my just be the carb(i dont know much about holleys cept to set idle). I will be in 3rd and mash the pedal at around 55 or so and it will sound fine and pull good for a few seconds then i feel a surge were it will pull even harder.
I have the vacuum plugged to the port that is highlighted on the carbs instal instructions (lowest port on the pass/front side of carb).
Finaly to my question: does all this timing seem right. It seems like the 60 total on the vac is a bit much. I tried to adjust the cannister to no avail. currently it is in the far CW position. I know that 36 total mec is where i want to be but the 20 inital is kinda fishy but it starts every time. so far i havent heard any pinging but i want the timing to be where it should be.
i find a lot of info on mechanical timing but never what vacuum should be. any suggestions would be much appriciated.
if i missed any details you need let me know

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post #2 of 3 (permalink) Old May 30th, 01, 08:17 AM
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Join Date: Aug 2000
Location: seattle, wa
Posts: 172

I would back off the timming a tiny bit. Remember to plug the vacume before adjusting.
Reset the mixture too.

Stock 67 327 RS
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post #3 of 3 (permalink) Old May 30th, 01, 02:35 PM
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Join Date: Sep 2000
Location: Washington, Michigan USA
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You don't have 60 total - the vacuum advance doesn't operate at high load/low vacuum conditions, so you don't count it. "Total" is base timing (set with vacuum advance disconnected) plus whatever centrifugal is added by the distributor. 20 initial sounds pretty stout, and you say you're not getting any vacuum advance at idle with the distributor connected to the front port on the Holley? Is it the front port on the carb base, or the port near the top of the front metering block on the pass. side? The latter is "ported" vacuum, which provides no vacuum at all at idle, and the front port on the carb base should be full manifold vacuum at idle. I think you'll prefer manifold vacuum to the distributor for improved throttle response and smoother idle.

Your total advance at 34 degrees is right on the money, but with 20 degrees at idle, it sounds like your centrifugal is already starting to come in (too early). 12-14 degrees is more common.

'69 Z28 Fathom Green
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