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Old 05-26-2011, 11:28 PM
70temp455 70temp455 is offline
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Default How much Manifold vacuum at idle

What amount of intake manifold vacuum is normal ?
I hooked up my Mity Vac to my intake to use as a vacuum gage and it showed 19 lbs of vacuum. Is this right and normal.
Thinki back I vaugley remember setting Idle mixture to best vacuum so I did taht and it was way rich so I cut the mixture screws back to where each just made about 1/2 lb drop on vacuum.
I keep saying my 72 350 is worn out but I just got my gauges hooked up and I have avg. 35 lbs oil pressure while driving and haven't seen less than 25 lbs at idle when up to temp. So it may not be as worn out as I originaly though.
Although I may have a head/valve issue. Itryed the dollar bill test at the tail pipes and it did suck the bill to the pipe occasionaly.
Thanks,
Andy

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Old 05-27-2011, 09:06 PM
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GStage1 GStage1 is offline
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17-19 is typical of max vacuum draw...you can use your mixture screws to set max vac and then use the vac gage to set max vac for timing.

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Old 05-28-2011, 06:30 PM
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PunchT37 PunchT37 is offline
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19 is about what a stock engine would pull. Run a compression test and a leak down test to verify the condition of the engine.

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Old 05-28-2011, 06:32 PM
pont3 pont3 is offline
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Quote:
Originally Posted by GStage1 View Post
17-19 is typical of max vacuum draw...you can use your mixture screws to set max vac and then use the vac gage to set max vac for timing.
Can you expand on the "THEN use the vac gage to set max vac for timing". I've never heard this before. Thanks, and, I appreciate the excellent advice you've been providing here.

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