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Discussion Starter #1
Ok, by now everyone must be tired of my 390 tuning questions but here is another...

It is only pulling about 14 psi of vacuum on the manifold port. It's pulling about 13.5 psi at the base of the carb. It's pulling about 13 psi at the power brake booster.

According to the shop manual, it should be pulling 17 psi.

Would a vacuum leak anywhere in the system cause the engine to pull less vacuum? I don't think so, but what do I know! Would dumping my 750 cfm Speed Demon and replacing it with a 600 or 650 cfm increase vacuum?

In order to pull that much vacuum, I had to set the timing to about 28 degrees btc. I re-sprung the mechanical distributor to advance a total of 20 degrees more. It starts advancing at about 800 rpm and stops at 4500 rpm.

Oh yeah...it leaks oil AND transmission fluid too...:)

Ken
 

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The ideal vaccuum is 15-20hg if your in that ball park, I wouldnt worry about it. If you adjust your air/fuel mixture on your carb to get the most A/F mixture, either by more vaccuum or rpm, and then re-adjust your idle, you should be fine.

If you have a vaccuum leak, and hook up a gauge, the needle will bounce, if it stays put, there is no leak. And if you have a leak, you will draw less vaccuum cuz its not all going into the motor, its leaking out. The trick is finding it, intake gasket, carb gasket, the pipe plugs, brake booster, etc.
Oil and tranny fluid wont have an effect of causing a vaccuum leak, unless its an intake gasket.

Rick
 

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Finding a vaccuum leak in a Cougar is real hard, it could be an endless hunt. headlight switch, booster, hoses, headlight pump, intake gasket, the can under the fender,etc. Hook a gauge to all sources and check for bouncing needle. Have fun.

Rick
 

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with some tuning, i can get my car to pull about 22 inches of Vacuum. currently its around 20 though. it seems to ping a bit when i advance the timing far enough to get the magic 22
 

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Discussion Starter #5
That's what's really odd about this...to get that much vacuum I had to advance the timing to about 28 degrees. Add in the 20 more from the distributor and believe it or not, no pinging!!!

I'm wondering if they speed shop screwed up the cam install or if it's an aftermarked harmonic balancer and it slipped...
 

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You might not be able to get more vacuum. It will depend on what camshaft you have in there! I can't remember what you're running in there, but if the cam has a lot of overlap, you'll get the lumpy idle and lower manifold vacuum.
 

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Discussion Starter #7
Cougrrcj...

I have no idea what cam is in it!!! The PO can't remember and neither can the speed shop that did the work...:(
 
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