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Discussion Starter #1
What does it mean when you get max vacuum at the point of the idle mixture screws set at 1/8 turn out from all in (closed)?
(All four corners)

What does that tell you?
 

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That the idle feed restriction is too large in the metering block. I feel it's best if they are out 1-1/4 to 1-1/2 turns.
 

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Discussion Starter #3
What does that mean? How do you get a smaller idle feed restriction?



I set my idle mixture screws 1-1/2 turns out. Then started adjusting all 4 until I had the most vacuum. It turned out that they where onlY 1/8 turn out from being closed. I made some passes and the truck acted-up. So I turned all 4 mixture screws 1/2 turn out. Much better but pig rich at idle. 60ft, et and mph picked back up to it's norm.

I was just wondering the cause and effect. (I'm going to change the setup next week to what the Quickfuel rep suggested and see how that works.)


Thanks
 

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It's easy to experiment with the idle feed restriction on the Holley style carburetor. What I recommend doing is getting a piece of stranded copper wire, stripping the end, cutting it off and using one of the strands to hook through the existing idle feed restrictor. Most of the time they will be about .013 diameter, just use about a 1/2 inch long piece that you can place in there and bend over so it can't come out unless you remove the metering block.

Try it, start at 1 1/2 turns on the screw and see how it responds, you can do it in the back and in the front. If it's better then you know that you need to go to a smaller idle feed and by about how much less area. A couple of thousanths can be a big change and make a real difference in the part throttle driveability.
 

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Sorry for stepping on the thread but what is the best way to set 4 corner idle setup? Have a quickfuel/proform set at 1/2 turn out on each corner and rear butterflies closed which idles at 850 - 900 rpms with a slight surge idling in gear.If I set rear butterflies like the fronts I get an instent ( quick) bog even though rear pump shot is adjusted right. For the most part I know my way around holleys but even though it runs great and fastest with this tune it doesn't seem correct.
 

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Discussion Starter #6
I adjusted all four at the same time. Adjusting each one 1/8 of a turn.

One of the problems I was having with the idle mixture screws set at highest vacuum, was that I had a slight studder / bog off the line. Went back and turned the screws 1/4 turn out and studder / bog went away and et/mph came back.
 

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Exactly what I get with the secondary buttetflies cracked even with the pump shot adjusted correctly. Seems everyone thinkls the p/s should be set exactly the same but for whatever reason I can not get it set correctly that way.
 

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I think that as a rule of thumb, at idle the transfer slot should look "square" more or less. Meaning that it's about as tall as it is wide under the throttle blade. If it's open more than that it can make the idle mixture rich and tough to control with the screws. Also, it can cause a lean spot when transisioning from closed or part throttle to open enough for the main to start flowing.
 

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I was going on the rule of thumb, just seems if I go anymore than just contact the butterfly shaft it will cause a quick off idle dead spot. I may try messing with it again.
 

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i have used staples as a restrictor as dave was talking about if you bend one end straight they work perfect if they need smaller in diameter then you can file staple
 

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Discussion Starter #12
I went down too 74 jets and the idle mixture screws liked to be out 1-1/4 turn out.

Now I have 72 jets and they seem to want to come further out. Haven't made it to the track yet with the 72's.
 

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Great post here, and thanks for the links as always Danny. I'm going to try this on my Holley 850 DP. I set mine for the highest vacuum just like Josh, and mine are almost all the way in too. Anything more than that, it idles very rich and the engine shakes quite abit. :shock: I'm going to step up to a Quick Fuel 950 soon anyway, but my brother is getting the 850 for his "472" 47 Ford Truck. Thanks alot for the information Dave. 8)
 

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Discussion Starter #14
One thing I noticed is that, setting the Idle mixture screws to max vacuum makes the engine very responsive for street driving. Yet I lose power on the drag strip. I end-up having them turn back out until it's black puffs coming out of the exhaust.

Plugs are starting to finally look right. I'm still going to try it with out the power valves as soon as I get some 82-86 jets.
 

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Cool thread. I have been fighting demons in my 770 truck Avenger at idle and transition phase as well. I finally ditched the Avenger metering block to loose the checks in the main circuit of the primaries.

I used a regular 4150 block and it was still rich at idle so I experimented with the idle feed restriction wire. Lowered the primary jets and it made a WORLD of difference! No hesitation and I like the way the annular boosters respond!

Kinda started a quest now to see if I could squeeze everybit of economy I can. Got my vacuum gage and 02 sensor in the cab. I really want a proform or quickfuel so I can tailor the Air bleeds as well.
If I can make it to 8 MPG I will be tickled. Getting 7 now. Was REAL rich at idle and cruise. Going down in jet size helped and I think I can go down one more step. Just have to wait till they get here. I picked up 1 mpg over 2 full tanks whith the jet change.

That may not sound like a lot, but it gets me from home, to my camping spot and back on a full tank. 10 miles less and I have to stop a crappy gas station instead of my normal one...


Jones, You race a super cab truck correct? Does it have the 2 piece drive shaft with the center carrier bearing?
 

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Discussion Starter #16
Broncman said:
Jones, You race a super cab truck correct? Does it have the 2 piece drive shaft with the center carrier bearing?
Yes, I drag race and still running a 2 piece drive shaft. It is too long for a one piece. I had everything replaced and rebalanced.

1.86 60ft with 3:50 gear, 28 spline mini spool, 29x9 Drag radial and stock leaf springs.

I just check it every so often for grease and slack.
 
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