Vacuuum is 15 at idle

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hotrod swinger

hotrod swinger

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Just checking to see if this is a good reading. Needle is steady.

170 fresh stock rebuild
Two barrel carb
2.5 exhaust

Thanks!

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How many miles on it? Might be a tick low. Where do you have the initial timing set?
 
hotrod swinger said:
Probably no more than 1000 miles. Initial timing is 12.
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Is the engine stone stock? The original 170 in Vixen liked 15. Does it run good where it is? If so, leave it there until it's first oil change and recheck it. Once the rings seat in good, that vacuum measurement might climb some.
 
The engine is stock. It runs good. There might be room for improvement. Now that you mention timing I haven’t spent any time fine tuning it after breaking it in. I’m going to bump the timing up a bit and make some adjustments.
 
As high and steady as you can get it, with optimum timing and smoothest idle. Is that a stock cam in there? If so I'd say that reading is a bit low. What is idle rpm?
 
hotrod swinger said:
What is the range for best idle vacuum?
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I would not be surprised to see an engine in good and BROKEN IN hit 20 or more. The broken in part is important. I'm not sure I'd mess with it just yet. Give it some more time and see what happens. Mine liked 15 initial......but not 16. Anything above 15 and it produced a rough idle. As long as it runs well, I'd let it break in good and then try to put the super tune on it.
 
I think it’s running good but I don’t have an odometer and I haven’t gone on any long trips so there may even be less than 500 miles right now.
 
I'd expect you to be able to see 18-20 in the vacuum gauge.
 
Turned out to be a vacuum leak. Carb gasket. Engine backfired when I first lit it up. Distributor was out.
 
valve lash will change your vacuum as well, just so you know.
I never pay much attention to idle-vacuum number measured at the carb-base, because there are just too many variables that mess with it, and IMO, it matters not much, cuz vacuum can change in a heartbeat with any change in rpm.
Cam timing changes it.
Ring-seal changes it
valve lash changes it
Ignition Timing changes it
Rpm changes it
A faulty PCV can change it
Even the exhaust system can change it.
And on a slanty, several other things can change it, and
As you have discovered, leaky gaskets can change it.
Happy HotRodding
 
But you still want it to be the highest and steadiest it can be on"your" engine. Whatever that is. Mine runs almost 20and rock steady when all is right
 
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