timing without a light
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Fleet Mechanic
Joined: Sep 2004
Posts: 1,674
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From: Rowland Heights
timing without a light
Wondering if one could adjust/check the timing by just using a vacuum gage. Engine is a 390 that runs good but does pop out of the carb once in a while. Water temp is 200 to 215. Suspect timing but need to get a light. I have a gage and figure I'd try this first.
Cargo Master
Joined: Apr 2004
Posts: 2,574
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From: Golden, CO
https://www.ford-trucks.com/forums/s...d.php?t=296937
Probably more than you wanted. The vacume guage at least quantifies something, but it's no replacement for a timing light.
Probably more than you wanted. The vacume guage at least quantifies something, but it's no replacement for a timing light.
Posting Guru
Joined: Jul 2003
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From: Eureka, Ca.
Originally Posted by edsf100
Wondering if one could adjust/check the timing by just using a vacuum gage. Engine is a 390 that runs good but does pop out of the carb once in a while. Water temp is 200 to 215. Suspect timing but need to get a light. I have a gage and figure I'd try this first.
Fleet Owner
Joined: Jan 2004
Posts: 26,007
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From: Brentwood,CA
kragen has them from 25.00. the vacuum gauge idea works great if you have the time to do it. i set mine to run a perfect vacuum of about 23 then brought it down to 20 to prevent pinging. it runs strong and after hooking up a timing light it showed 13 btdc.
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FTE Leadership Emeritus
Joined: Jul 2002
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From: Long Island USA
Timing with a vacuum gauge was great when you had the idle vacuum spec, but that sort of timing method went out with oil-bath air filters and flatheads 
I remember reading old Chilton/Motor's manuals and they had an idle vacuum spec, but there's really no way to get it right these days without a timing light.
Actually, I think back then it was more important to make sure you had enough vacuum than to get the spark timing perfect.
I remember reading old Chilton/Motor's manuals and they had an idle vacuum spec, but there's really no way to get it right these days without a timing light.
Actually, I think back then it was more important to make sure you had enough vacuum than to get the spark timing perfect.
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Posting Guru
Joined: Jul 2003
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From: Eureka, Ca.
Yes, from the front the port on the right (drivers) side is full vacum. the other is ported (no vacum at idle). Just to be sure pull the hose off while the truck is running if you have vacum at idle you have the right port.
Post Fiend
Joined: Mar 2004
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From: Union, Washington
Originally Posted by Randyb12
Yes, from the front the port on the right (drivers) side is full vacum. the other is ported (no vacum at idle). Just to be sure pull the hose off while the truck is running if you have vacum at idle you have the right port.
Last edited by Bear 45/70; Jul 29, 2005 at 12:33 PM.
Posting Guru
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From: Eureka, Ca.
Originally Posted by Bear 45/70
Running manifold vacuum at idle is not correct. There is no vacuum at idle on the ported vacuum port so you will run initial timing at idle (the correct way). You only want vacuum to the dist. when at higher rpms. The vacuum advance is to help gas mileage, not correct idle problems or incorrect adjustments. If you are after high performance then run no vacuum as all. Real race motors run mechanical advance only or electronic advance if timng is computer controlled
Unless I misread his post. If he was asking for the dist. He wants the ported one on the left.