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Discussion Starter #1
I was hoping someone could explain how a Hollley power valve works. My understanding is once the set
vacuum is reached it richens the mixture. How long does in richen the mixture? Does it keep adding fuel
tell the vaccum goes higher then the rating, does it have a set amount of fuel it will discharge per event?


1966 Mustang Coupe, 302 custom roller cam, holley 650dp,http://www.289mustang.com
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That is it basically, vacuum drops valve opens,vacuum rises above rating valve closes.
How much fuel? well there were 3 Types of valve 4 hole 6 hole and slotted(picture window)
The current type is basically of the slotted type, the ones with the hole offered less flow potential.But the Power Valve Channel Restriction is what meters the flow from the valve to the main well It is the size of the PVCR's holes that controls the amount of fuel

Greg B
 

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What are you up to Bill?

Power valve is a minor detail, as long as it's working....

With your cam and compression, I'd say a 45 would be fine....

You might be surprised that pinging is largely independent of the air/fuel ratio as long as it's within the normal range....your plugs are telling you that it is...

It's real simple...the fuel just isn't up to the cylinder pressures being exerted at WOT at low rpms....

You should hear how crappy the race car engine runs on pump gas, even with Super 104 in it....drain the tank, pop in some 112 race gas and it just purrs.

Pat
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Discussion Starter #4
I'm just trying to get a full understanding of all the functions that could be related to my problem. I was thinking about trying a power valve closer to my idle vacuum. My idle vacuum is around 9 my power valve
is a 6 (i think). It was suggested to widen my mechanical advance, I have a 15L and a 10L arm on the advance, can you get a 12L arm? I'm on the 10L now (20 degrees of advance) 30 is to much!

1966 Mustang Coupe, 302 custom roller cam, holley 650dp,http://www.289mustang.com
http://www.289mustang.com/images/vmfcar.jpg
 
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There are two different advance cam assemblies 10L-15L and 13L-18L

Greg B <P ID="edit"><FONT SIZE=-1>Edited by SuperCJ on 03/30/01 06:51 PM (server time).</FONT></P>
 

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Bill,

Try disconnecting the secondaries and see what happens with just the primaries working...

I'm curious as to what happens at "psuedo WOT"...*G*

I just don't want to see you whirling dervishly on this problem....you can chew up a lot of time chasing detonation around...

Pat
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Mac's totally oversimplified theory of the operation of a carburator

A carburator is essentially a static device that switches its mode of operation at very specific notches that correspond with what the motor is doing. The carburator senses this by the level of vacuum or lack of vacuum that it is receiving from the motor. At idle it is operating on the idle circuits. At a certain point it dramatically switches to the primary jets. At another dramatic point it adds in the secondary jets. Thats pretty much it. The accelerator pump or pumps are activated momentarily to cushion the dramatic change in throttle opening. Without them you would get small duration lean outs every time you quickly open the throttles. This is caused by some lag between the time that the throttle is opened and the motor begins to flow at the new throttle position.

At some point back around the dawn of the discovery of vaccum the carb elves decided that your primaries needed something more. If the jets are calibrated for low rpm cruise around you would have to engage the secondaries every time you go up hill or pass another car at light moderate throttle. That would put in way too much throttle and also kill mileage not to mention that it would be downright annoying, LOL.

TAAA DAAA!! Enter, the primary circuit power mode step. In some carbs its a step in a needle that slides up and down inside the actual jet and changes its operating size. In the Motorcrafts(most?) and Holley's its a diaphram switch or vacuum valve. Higher vacuum levels hold it closed which blocks some tiny auxiliary fuel channels. At some lower vacuum level as determined by the valves calibration it is released or opened which enables the small fuel channels to deliver a predetermined amount of extra fuel into the mix. This fattens up the mixture a bit and over comes the moderate throttle lean motor syndrome.

Some carbs also have secondary power valves for even more fuel at wide open. These are usually needed on BIG FLOWING motors where you almost can't get a big enough jet at wide open.

With the typical stock motor making 17-20 or whatever inches vaccum at idle it has been predetermined that a power valve that opens as the vacuum level in the motor decreases to 6 1/2 is sort of generally around the best probably for most situations with most motors in most vehicles most of the time, LOL. Thats what you usually get from the factory.

Since your motor makes only 8-9 inches of vaccum at idle it may need a somewhat lower rated power valve. The general rule of thumb is take your idle vacuum number / 2 and round up or add .5. That hasn't worked so far in my motor so I run a plug.







You can see my 65 fastback at: http://hottarod.stangnet.com/
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Your descriptions of how stuff works is the most elegant, yet simple, texts I've read. It is informative not only to the layperson, but to the expert. You really ought to write a book... or teach somewhere.

http://clubs.hemmings.com/baymustang/platesmall.jpgLet me check your shorts! My multimeter is just a-waiting! Formerly known as Midlife in the old VMF.
King of the Old Farts *struts*
 

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Hey he did....*G*

At least it'll show up in search now....like anyone uses that!

hehehe

Pat
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Discussion Starter #11
Wow, that's good stuff. I'm real good at getting my 2 stroke dirtbikes tuned, I've developed a ear for it.
The car enine is a little more of a problem for me. I'm going to set everything back to where I started and
try disconnecting the secondaries. It is easy to get to many ideas going at once!

1966 Mustang Coupe, 302 custom roller cam, holley 650dp,http://www.289mustang.com
http://www.289mustang.com/images/vmfcar.jpg
 
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