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I am having a major "too rich" issue. Holley tech told me to measure the vacuum at idle and divide that # in half to get the power valve size to go in it. So I went and bought a combination vacuum pump/checker and hooked it to the PCV vacuum hose. It only reads about 2.5" of vacuum at idle and the number goes up as i rev the motor up. Then I hooked the vac gauge to the other vacuum line that goes to the tranny. Same thing. Reads about 2.5" and the needle shakes like crazy. Needle goes up as you rev it. Am I checking this right? The motor has a .629/605 lift cam in it and supposedly has about 300 miles on it. The fuel pressure gauge near the carb runs at about 7.5 psi until it warms up - and then it goes to about 3. I really don't know if this is an accurate reading or not - on the other thread a bunch of guys said it was probably the gauge. I drove it about 40 miles last night and It never quit - so it must be ok. The car runs extremely rich - I checked the oil when I got home and it looked like it had gotten some fuel mixed in with it. Puts out a ton of fumes. Smokes when you first start it. It seems to run ok when you stand on the gas, but seems like it is cutting out a little at say 40 mph (2500 rpms) Sorry for the length of this but I need help!
 

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Is this problem based on the "396" in your signature?
I'm not going to suggest anything yet but will ask for some info that might help to narrow down the problems.
1 Do the idle mixture screws have any effect; you should be able to stall the engine if one of them is turned all the way in.
2. What's your initial timing at and rpm.
3. What are the current pv's/pv in the carb.
4. Are you sure all unused vacuum ports are plugged.
 

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shawn63 said:
Is this problem based on the "396" in your signature?
I'm not going to suggest anything yet but will ask for some info that might help to narrow down the problems.
1 Do the idle mixture screws have any effect; you should be able to stall the engine if one of them is turned all the way in.
2. What's your initial timing at and rpm.
3. What are the current pv's/pv in the carb.
4. Are you sure all unused vacuum ports are plugged.
If #4 was a no you would run lean(er), if you unplug a "manifold vacuum port" does it get better or worse? What size jets are you running?
 

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I know you had your cam specs posted before but I forget them....how much duration does your cam have...tons of duration will cause your engine to have low manifold vacuum...thats why some cars with "big" cams cannot run power brakes or have to run a vacuum storage can to make their power brakes work...just a thought...dont want you to be chasing a ghost looking fo a cure to the vacuum issue when the real cause might be the cam itself...:)
 

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Discussion Starter #5
I know you had your cam specs posted before but I forget them....how much duration does your cam have...tons of duration will cause your engine to have low manifold vacuum...thats why some cars with "big" cams cannot run power brakes or have to run a vacuum storage can to make their power brakes work...just a thought...dont want you to be chasing a ghost looking fo a cure to the vacuum issue when the real cause might be the cam itself...
info off the cam card; "valve adjustment" :intake .028 ex .030 - "gross valve lift": in .629 ex .605 "duration at .020 tappet lift": in 295 ex 304 "Valve timing at .020" int open 40 btdc close 76 atdc exh open 80 bbcd close 44 atdc. It then says "these specs are for cam installed at 108 intake center line" Then it says "duration at .050": intake 260 exhaust 266 "lobe lift" in .3700 ex .3560 "lobe separation" 108 Then "recommended cc valve spring"

Quote:
Originally Posted by shawn63
Is this problem based on the "396" in your signature?
I'm not going to suggest anything yet but will ask for some info that might help to narrow down the problems.
1 Do the idle mixture screws have any effect; you should be able to stall the engine if one of them is turned all the way in.
2. What's your initial timing at and rpm.
3. What are the current pv's/pv in the carb.
4. Are you sure all unused vacuum ports are plugged.


If #4 was a no you would run lean(er), if you unplug a "manifold vacuum port" does it get better or worse? What size jets are you running?
Yes it is the 396 in the sig. I haven't messed with any adjustments on the carb yet - I didn't want to mess anything up worse. There is an idle mixture screw on both ends of the carb (primary and secondary) Correct? The small screws on the side of the metering block? Initial timing - don't know. I don't have a timing light yet and don't have any specs on what it should be set to if I did. I also don't know what power valve is in the carb yet. I'm wondering - if I truly have only 2.5" of vacuum at idle, can you get a say 1.5 power valve or should I just get one of those "power valve block off " plugs and not run one? Don't know what size jets. There are only two vacuum ports - one on the intake that goes to the pcv and one on the carb spacer that goes to the tranny. I tried both sources with the gauge. There is also a small vac port on the top side of the carb that is capped. Sorry I sound like an idiot but I hate to go screwing with something I haven't worked with in over 20 years without some guidance. The local speed shop is backed up about a month and I'm having trouble peeling my race engine guru buddy away from his business (250 miles from me...) Any help appreciated. I printed off some info on setting up a Holley from another site - but the "low vacuum" has me stumped. Keep in mind I've never owned a high performance motor like this is looking like.....
 

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duration @ .050": I260/E266 degrees is a pretty big cam...Your likley not going to have a ton of vacuum. Now I think 2.5" of manifild vacuum is pretty low but that still might be right where it should be with that much duration...you could try adjusting the idle mixture screws with the vacuum guage attached until you get the highest vacuum reading you can get...Now you said the cam has about 300miles on it...does the rest of the motor have that few of miles on it too or could it possibly have more? The smoking at startup could very well be worn valve guides that are causing that to happen...and the gas in the oil could be the rings being worn too...just some thoughts...not saying this is what is happening....good luck..:)
 

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2.5" is way way too low...you got somethin else going on, plus you said if you give it gas the gauge goes up...should go from there down to zero
 

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Do you knww if the carb is in "out of the box" condition?
If so it probably has 6.5 pv/pv's; the rear may be blocked.
AS mentioned try adjusting the idle mixture screws; start with the primary side, slowly adjust each one for highest vacuum. You may find you gain vacuum by this. IF the screws have no effect then you have another problem which we can get to later.
You really need to get a timing light; beg borrow whatever. From the sounds of it you don't have vacuum advance on the dist. not that it would be doing anything at this point. Without any vacuum advance you'd probably need around 20* advance at idle as a starting point anyway. Timing can also greatly increase manifold vacuum. IF you increase the initial timing you'll need to confirm total timing so as not to run into detonation problems. You'll probably find that the idle speed increased as you tune and you'll probably need to adjust it accordingly. Each time you adjust the idle speed you should then readjust the idle mixture screws and check the timing.
The small vacuum port you mentioned is for dist. advance and is not manifold vacuum; leave it plugged. IF you ever decide to use vacuum advance use manifold vacuum for a source as that port is more of a emissions oriented thing.
You can buy 1.0 pv's but I'd think you can improve your low vacuum problem by simple tuning.
To get things right though you need to confirm what pv is in the carb and select one as suggeted by the holley tech after you've tuned to achieve peak vacuum.
I don't know much about solid cans but I'd think if the valve lash wasn't set right it could lead to some problems as well
 

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First thing I would do is verify initial and total timing. You said you need a timing light, so go get one. I recommend running vacuum advance and have that connected to a manifold vacuum source. Your motor will more than likely like 36*-38* of total timing (with vacuum advance disconnected and the port capped).

Once you get the timing squared away, remove the carb and verify that the idle transfer slots are only opened .020". The idle transfer slot should appear as a square if they are opened .020". If the idle transfer slots are opened too much, you will have an overly rich idle and the idle mixture screws will have little to no effect on the idle mixture.

Here's a blurb from CarCraft about power valves:
PV Wives Tales

For years, magazines warned the world that running a power valve with an opening point below the idle vacuum would dump all kinds of fuel into the engine at idle, foul plugs, and waste fuel. The whole idea of a power valve is to allow you to run leaner jets in the main circuit and still add fuel when load increases. The truth is that the power-valve circuit is completely separate from the idle circuit, so if your engine idles at 7 inches of manifold vacuum and the power valve opens at 8 inches or lower, the power valve will open at idle, but the engine will not receive any additional fuel until the main metering circuit begins flowing fuel out of the boosters.

However, if your carb is set up this way, with a low idle manifold vacuum and high power-valve opening point, it will run rich at part-throttle since it's likely that the power valve will be open much of the time. So, the smart move is to install a power valve that opens at a lower point, such as 4 or 5 inches of manifold vacuum instead of 8. Your engine will be much happier and run much crisper under light acceleration. There are 11 Holley power valves available with opening points ranging from 1 to 10.5 inches of manifold vacuum.
 

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I agree with everything said but will also add that if the carb has been sitting awhile the metering gaskets can and usually do shrink up and hemorage so the carb goes nuts. Don't over look bad gaskets as a very real possibility of a problem. RM
 

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Also, consider the possibility of a blown power valve. Easy to fix but if you experienced a backfire, this could be the issue.
 
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