I will say from experience, float level has never affected my cruising and part throttle. Wide open I have had low levels run the fuel bowl empty and cause lean conditions from a poor fuel pump. But also my adjustments were small for float level.

 

im new to this...and still learning so someone slap me back into my place if this is incorrect, but i think you're looking at it wrong. up until yesterday i was looking at it wrong too...or atleast i will be taking this new approach to tuning when my truck is back on the road.

it seems to me that you're thinking of the primary as part throttle and the secondary as wide open throttle. from what i'm gathering, both the primary and secondary mains are for part throttle, and the power valve channel restrictors are there for WOT enrichment....and the power valve is there to determines how soon/late you reach that enrichment rate.

if you're familiar with tuning EFI, just think of the power valve as the enrichment rate and the PVCR as the commanded power enrichment AFR. i come from the EFI world so relating the parts is helping me lol.

from my extreme noob point of view reduce the IFR until your light throttle tip in leans up to your desired ratio. this could also help with your extremely sensitive idle screws.

then attack the mains and i'm still digging into what approach to follow on this part. i see some tuners stay with the factory jet spread, and others go directly to a 10 jet spread. then from there they will play with the PVCR to get WOT performance and the bleeds to make the AFR follow a consistant AFR through the transitions from the idle air bleeds to the mains. do i have this right in my head? lol

 

You may be right as I've not messed with it yet.

But the thing is I'm not missing the powervalve at all. I'm not lean anywhere in the fuel rpm curve. The car runs great and tuning became a breeze when I could see what each fuel circuit does on the wideband rather than be drowned out in a sea of 10/1 pig rich powervalve enrichment.

I'm not saying that everybody can run this way but my little mustang shure hasn't noticed it's gone.

 

if the power valve is opening too soon, you could go bigger with it...

or just leave good enough alone

 

That's the way the QF acted out of the box. Like the PV was opening WAY too soon and often

 

at what RPM was it going rich? maybe you just had a faulty power valve? i dont think it should activate until around +-2,500 rpm.

 

It would shoot to pig rich at any rpm if the vacuum dropped.

But keep in mind that with a 3 speed trans and 3.27 gears on 25" tires I don't spend much time under 2k even driving like grandpaw.

Folks say and literature indicates the PV shouldn't be in play but my wideband and blockoff plug says otherwize. Even if I delay it though my engine just isn't missing the fuel it's throwing, I'm still a little rich in places on the stock jetting and restrictor spread with the powervalve in the glovebox.

 

the power valve operates on vacuum signal. it is completely independent of rpm. if you are doing 1000 rpm in 3rd gear and put the pedal to the floor, the throttle blades open and intake vacuum goes to near zero, the power valve opens and flows fuel.

the power valve stays closed and does not flow any fuel when vacuum is high... specifically above the vacuum rating of the power valve. the intake vacuum pulls the power valve closed. what can happen with a power valve is when they actually go bad they don't seal and always leak or seap fuel under any vacuum condigtion. but what can also happen is you have the wrong size/rated power valve- if your engine produces a weak vacuum signal at low rpm no load then it's not uncommon for a standard size power valve rated around 5 or 6 to be open and flow fuel, you need to use a power valve with a lower number. hope that helps, and you found the buttkick funny

 

I think I'm in the mood for another round of carb tinkering.

I'm a tiny bit rich at low low speed and my idle screws are super sensitive. So I ordered a pair of .030 IFR jets to try in place of the stock .035"


Then my plan is to use the .035 restrictors in the power valve feed in place of the .055 and try to phase back in a 3.5 power valve to see how it behaves


I also think I need to reset my primary throttle opening as I have an ever so slight hesitation at very slight throttle

So look for updates in the near future

 

sweet. your thread is helping me a ton.

 

I pulled the carb off today expecting my new IFR's to come I, but I didn't catch the "on the next business day " on my delivery confirmation.

But since I had the carb off I decided to go ahead and throw my trusty 3.5 power valve in place of the blockoff plug I was running. I rechecked my vacuum readings and hot idle in pull 10" in N and that reading drops to 7 in gear and even less if the engine isn't up to temp fully. So obviously the quick fuel supplied 6.5 was a non starter.

Anyways I put the powervalve in and resquared my transition slots slightly (which made my off idle lean stumble WORSE btw) and took the car for a drive.

Midrange and low end torque especially without downshifting is notably improved however upper end power after the secondaries come on has been harmed a great deal primarily from the pig rich condition that now exists at WOT. Here's roughly how the transition shakes down.

Rolling along in 3 rd no downshift starting at 2500rpm or so

Part throttle low 13'ish that leans out somewhat towards 15 as I apply more and more throttle,

Watching the wideband you can see where the power valve opens and AFR drops back into the low mid 11's and stays there as more and more throttle is applied till the secondaries come on then it's full on pig rich 10's or less all the way out through the rev band.

SO here I sit pondering how I want to correct this.

1. Cut back on the power valve jets significantly

2 cut back on the secondary jets a great deal

3 cut back on both slightly and see if I can lean things up a little before AND after the secondaries open.

3 seems like the logical course but the question is how much change would be a good starting point? Four sizes seems about right for the secondary jets but I have NO CLUE at all how the powervalve restrictors respond to changes.

 

http://forums.holley.com/entry.php?4...r-Valve-Tuning

the way to choose a power valve initially is idle in gear and divide that vacuum reading by 2. 7 / 2 = 3.5.

fyi in case you or anyone doesn't know, the fuel circuits in a carb at least the holley 4150 are supplemental. it starts with the idle circuit, throttle blades are closed so only way fuel gets from the carb into intake manifold is through the idle mixture screws in the metering block. when throttle blades open slightly, it exposes the transition slots in the primary bores, now fuel flows through them plus the idle circuit. as throttle blades open more and airflow gets high enough, the main jets in the primary side of carb come online and flow fuel out the boosters in the primary bore- now fuel is being supplied by the idle circuit, transition circuit, and primary jets.

The power valve supplies fuel only through the main jets and out the primary boosters, therefore if airflow is not high enough then the main jets aren't online and the power valve will have no affect. furthermore the power valve operates on intake manifold vacuum, when vacuum drops below a certain value (meaning high engine load) then power valve opens and flows fuel (i.e. power enrichment).

on your secondary side your carb is operated by vacuum secondaries- this means the secondaries don't open till airflow drawn through the primary side of carb is high enough and the vacuum signal from the carb primary bore (not manifold vacuum) going to the secondary diaphragm housing is enough to overcome the spring in there and open the secondary throttle blades. as airflow then increases through primary carb bore, that vacuum signal gets stronger to secondary diaphram housing further opening secondary throttle blades- cycle repeats and that's how the secondary throttle blades modulate themselves based on airflow the engine is pulling. realize that the secondaries and power valve operate independently- the secondaries on airflow and the vacuum signal created by that high airflow through the carb primary bore versus the power valve which operates on dropping intake manifold vacuum signal. as secondaries open, your primary throttle blades have to be open to allow for that high airflow, intake manifold vacuum further decreases making the power valve more relevant. so now fuel is flowing from the idle transition and primary main jet circuits, plus fuel is starting to flow through the secondary jets out the secondary boosters as those secondary throttle blades open, along with the power valve based on whatever intake manifold vacuum is doing the entire time.

going back to your initial post, you have a Comp 219-233 @109lsa cam on a 5.3L which i believe is a 323 cubic inch. your cam has fairly high overlap correct? that would mean low manifold vacuum at low rpm. you're also running this carb (http://www.holley.com/0-80670.asp) which is rated at 670 cfm ? generally a 450 cfm carb is for a 302/305 cid engine and a 650 cfm is for the 350 cid engine having a stock cam. that being said i would say your carb is slightly large for your engine in terms of cid but the motor is built for power and rpm therefore the 670cfm is the correct choice however you will have to adjust it to get it to work on that engine- don't expect the jet sizes or power valve it came with to work carb makers have no idea what type of engine it's going on they set them up for mild engines with small or stock cams. you will need a jet kit and a secondary diaphragm spring kit for starters.
my recommendation is to first make sure float level is correctly set, then adjust your idle mix screws in gear then don't touch them from here on out. now run easy on flat highway in 2nd, 3rd, and 4th gear between 2000 to 4000 rpm which will be light load- you will have your 3.5 power valve or some very low number one in there (or the plug) so the power enrichment circuit won't be supplying fuel to mess you up- now you're tuning to figure just primary jet sizes based on your wideband. once your happy with A/F ratio under those operating conditions where you no the power valve wasn't supply fuel nor the secondaries were opening, don't touch the primary jet size it is set.

now you have your idle, maybe/hopefully transition circuit, and primary jets done. next i would disable your secondaries by removing the linkage connection to the diaphram, actually i should have said this in the beginning for when you were tuning primary jets. now guess what you're going to figure... power valve. this can be tricky because you don't want to go into too high rpm where the secondaries should be opening. tuning here is where you want high gear high load at low rpms going up hills, where you push gas pedal down easily (not looking to make accelerator pump circuit relevant) and open the primary throttle blades. if your power valve # too low, you'll go lean and have no power. power valve too high and you'll go rich and stumble. for this tuning you'll want to go wide open throttle but keep rpms low enough where you should not need the secondaries, use your wide band to determine power valve #. and using a 2-stage power valve might benefit you i don't know but this is how you would find out.

once power valve set, move on to secondary side getting the secondary jets and the diaphram spring correct. one way to do it is put the heaviest spring in the secondary diaphram housing so the secondaries come in late, which would cause the engine to hit a wall at a certain power (airflow) level- it won't be a lean condition because your primary side and power valve is correct and the secondary throttle blades aren't opening but rather a momentary lack of power and loss of hard acceleration until rpm and airflow really pick up and the secondaries then open significantly. in a car this can be hard to deal with because you need a heavy load on the engine which means high gear and high rpm along with the time and distance to observe the affect.
once secondaries are opening significantly, and generally you can here them, your wideband A/F ratio will give you an indication of how you change those secondary metering jets.... then once you get those 2ndary jets to your liking you then go back and use lighter diaphram spring to help out with any loss in acceleration by making the secondaries come in sooner. the problem with using a light spring to begin with is you don't know when/how the secondaries should open, and when they come in early now it's another tuning variable you have to juggle with and you don't necessarily know which direction to tune. by starting at one extreme end you work your way in one direction knowing that's the correct direction, and you don't want to touch anything on the secondary side because it's supplementing what's happening on the primary side. if your primary side is not correct, then you chase your tail don't understand why now one thing is good but something else is bad and get mad.
after all that's done things should be pretty good, then you start changing one thing at a time such as power valve #, maybe a 2-stage power valve, accelerator pump cams and metering jets to get the most out of the carb for your operating condition.

- you said previously your idle mix screws are super sensitive. that is because your idle feed restrictors (IFR) are too big, if those are changeable you need smaller ones.

- "also think I need to reset my primary throttle opening as I have an ever so slight hesitation at very slight throttle" this goes back to where i said maybe/hopefully transition circuit. this stumble is generally a lean condition until the primary jets start flowing fuel. the way to increase fuel in the transition circuit, since all that stuff in the carb is machined in and not changeable, is to raise the fuel level in the primary bowl and/or richen the idle mix screws. now that will have an affect on the primary metering circuit and don't be surprised if that is now richer and you need to drop a jet size there.
check out: http://www.bob2000.com/carb.htm

 

What jet spread does the carb come with stock?

What is the stock primary jetting, and at what jet did it cruise ok with no power valve?

Secondary jet size?

Without the power valve, is wot afr where you like it?

 

72-82 stock and current jet spread.

Cruise AF is great above 2500 @15ish

Tiny bit rich below that.

No powervalve WOT AF is good hovering in the 13 range.

With powervalve pig rich


I've got some 77 secondary jets on the way to try to bring WOT ratios back into the "power range" with the power valve operational.

 

The overall tune is getting really close. I think if I pull back on the IFR's slightly and bring my WOT a f ratio in check I will pretty much be done

 

I went back into the quick fuel to make a few minor tweaks mostly taking out a little fuel from the IFR, PVCR jets and secondary main jets to bring my A/F ratios into the more optimal range at WOT

I also snapped this pic showing one of the main differences in the quick fuel slayer and the street avenger mentioned before and is in part why this carb despite all it's features over the street avenger is quite a bit cheaper. Instead of a secondary metering block you have a metering plate but unlike holleys so equipped you still have changeable jets as you can see.



It's really wet and cool so a road report may have to wait a couple days

 

That's interesting. Surely a way to cut cost.

 

And on a two corner idle carb I can't really figure out what the downside would be

 

I always preferred a 4 corner dp thinking that my rear 4 cylinders might be getting a different afr. Thinking single plane.

 

Well fellas I'm going to have to regretfully conclude this thread. I appreciate everyone's guidance here but my carbed LS is no more.

I got a trade offer too sweet to pass up for my ugly low budget LS swapped fox in the form of a clean RCSB 2000 gmc Sierra 4.3 auto commuter special.