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-   -   Advice tuning holley 600 vs idle circuit (http://www.hotrodders.com/forum/advice-tuning-holley-600-vs-idle-circuit-232158.html)

eric32 04-23-2013 07:07 PM

Advice tuning holley 600 vs idle circuit
 
Hello guys me again:) I need some basic advice here on tuning my holley 80457 600 vacuum secondary carb idle circuit. I know about basic carb tuning quite well but am by no means an expert like some of you guys on here when it comes to fine tuning a carb. first here is my setup

350 sbc
dart shp 180cc aluminum heads 72cc chamber
lunati voodoo hydraulic roller 270/276 219/227 @ 50 515-530 lift. 112 lsa
holley 600 vacuum secondary
weiand high rise dual plane
9 to 1 compression.
Turbo 350 2200 rpm stall 3.42 rear gears.

Ok here is my dilemma. I got the timing all set and with vacuum advance hooked up I have around 30 to 32 at idle and around 18 degrees initial timing and all in by 3000 rpm.

Motor runs excellent from 2000 rpm and up but in order to have proper transfer slot position on the primary's at .020 I try to crack open the secondary's about 3/4 to 1 turn past contact on the secondary speed screw but it will cause my idle to be to high and the primary idle won't go down enough but on the flip side of things if I leave the secondary's open too much like that its causing a lean condition and surging at low speed under 1800 rpm from the transition cirtuit and too high an idle and an off idle stumble and the pump shot has all been checked for proper clearance and gets a good shot of gas.

And if I set it back at half a turn then I can get idle to be good and takes off without the bad stumble and backfire from lean tip in and goes just fine but then I have the problem of the transfer slot being slightly more then .020 and say maybe around twice that amount but I still have good tuning of the idle mixture screws and they sit around 3/4 of a turn out.

I know the jetting is not bad as plugs are good and tan and no surging going down highway at 55 mph at 2600 rpm. So I am getting the feeling here but I could be wrong that the holley 600 is a little to lean on the idle circuit for this cam but I want to get this carb to work as getting something else is out of the question and I know a 750 is more power etc but this is something I want to drive and get decent fuel manners with better throttle response.

I do have a set of quick fuel billet aluminum metering blocks both primary and secondary and they have a feature of being able to change the idle feed restrictions from .028 ( which is stock size on current holley blocks) to .031 and would this help me with better idle tuning and needing less transfer slot if I swapped out the holley blocks for the quick fuel blocks which have more fine tuning features and are for this and the 3310 carb as replacement blocks with a more performance type fuel curve which I feel this carb can use. Any opinions? Thanks guys appreciate your help.
Eric

F-BIRD'88 04-23-2013 11:09 PM

Use ported vacuum and re set the carb for correct pri and sec T slot exposure at idle.
If that ends up being more than .020" so be it.

eric32 04-24-2013 09:14 AM

Hello Fbird I have tried that before and the engine does not like ported vacuum too well even with the previous smaller cam. From what I have read on the whole ported vs full manifold debate is bigger cams like full manifold for extra timing and a better idle and my engine runs better with full manifold then ported. When using ported I end up with the primary's open way too much and the secondary transfer slot is up higher then the front and making them equal ends up allowing too much air and I can't get the idle down to 900 rpm as the secondaries are open too much and by the time you get them right to work well they are not equal. I will try and see how it goes.

33Willys77 04-24-2013 11:11 AM

I am thinking you are opening the secondaries too far. Close them off and set the t-slot on the primaries to .020. I am not a big guru with Holley carbs, but doesnt this carb have 2 idle adjustment screws instead of the 4 corner? If so, then the seconardaries would be closed. F-Bird will set this straight since he is on here already. Others may also charm in, but this is what I am taking out of your post.

F-BIRD'88 04-24-2013 11:37 AM

The 2 corner idle carbs also idle on the secondaries. its just not user adjustable.
Adjust the secondary opening as required from the baseline setting.
You do not want them completely closed. If the motor wants more base initial timing at idle give it what it wants.
try 24deg at idle.

If you want to play with the idle circuit get a AFR meter/gauge.

eric32 04-24-2013 11:49 AM

Yeah this carb is only a 2 corner idle adjustment. Seems the carb is not too compatible with bigger cams then rv sizes. Can't afford a new carb right now and want to do what I have to do to make this one work and I just need to get it fine tuned to do so.

Problem is if I open the secondary's to be equal with the primary's it ends up with too much of a high idle and causes off idle slow speed surging issues but fine once rpm is picked up. Using ported vacuum does make my engine run with a little less throttle response on low speed and also makes it run a little hotter through town in stop and go situations.

But the primary's I can never get to be .020 or close to it without having to open the primary's open more in order for it to idle good and not stall when put into gear but defeats the purpose of getting it to be square and not end up with the idle pulling too much from the transfer slot and making a too rich of an idle.

This carb has a very lean idle circuit and that's why I asked if I use the billet quick fuel metering blocks it has replaceable idle feed restrictions and will allow me to change the idle fuel curve and might allow me to get better adjustability as this cam want's a richer fuel curve in order to idle well.

From what I read the holley 1850/80457 600 vacuum secondary carbs and there street avenger lines are set up with a very lean idle circuit and many people have had problems with these carbs being way lean out of box on anything other then a stock size or rv cam engine.

Even if I give it more timing initial and hooking the vacuum advance up to ported source it does not make any difference and I end up with the primaries open too much but the idle mixture screws still adjust but end up with run on after you shut the engine off.


I have not checked how much vacuum I have but should be around 16 inches so that is not a problem there as far as vacuum signal goes.

F-BIRD'88 04-24-2013 12:27 PM

If you are convinced the idle circuit is too lean then hone the IFR holes a .001" bigger.
Don;t get all carried away.

Give it more idle timing , first. If it runs on use a idle stop solenoid to allow the throttle to close when off.
Heavy dependancy on manifold vacuum at idle for idle advance will result in a bog when you rug it
as the idle timing disappears.
The .020" T slot pre-setting is not carved in stone. Give it what it wants. Adjust as required.

eric32 04-24-2013 12:49 PM

Thanks fbird I will try your suggestions. I know this sounds like a stupid question but where can I get drill bits that size to drill bigger in my original metering blocks? And is this done by hand or a hand drill? I have heard about doing that but have not seen it done. I am famaliar with what holes are what on the metering block. Thanks guys you all rock:)

F-BIRD'88 04-24-2013 01:44 PM

small pin drill bits sets can be found in many industrial tool supply stores.
harbour freight
princess auto etc.
I do it by hand. Very small changes make a big difference +/-.001 .002" hone the hole by hand.
very easy to get carried away.
What happens if you just simply reduce-restrict the PCV valve air flow? this should richen the whole idle circuit by default. If it helps just get a different PCV valve that flows less at idle. (smaller internal orrifice)
A lot easier to "trim" the idle circuit by manipulating the PCV valve air flow at idle.
There is a possibilty your PCV is out of spec. Non OEM part. Something simple to look at , first.

Get a AFR gauge to see if it is in fact lean. @ offidle transition. I do all my tuning with a simple low cost 3wire Heated narrow band type.

if when the idle mix is set at idle , the idle mix screws are less than 2 turns out, I doubt the idle circuit IFR is too small.
It is very very rare that you need to start drilling this and that, especially when other things can be manipulated, like the PCV valve idle flow spec.

eric32 04-24-2013 03:11 PM

I don't have the option yet for using a wide band 02 censor as I have to find someone who can install one for me and I live in a small town and not many around here can do exhaust work etc. As far as the pcv valve goes its a oem replacement type one so I have no idea what it goes too as the parts counter guy asked me what it was for I said a 350 small block chevy and he gives me one and said it covers most gm vehicles so don't know how to get a different one there and thanks for the tips on the pin vice drill bit set I will have to get one. I will try some other things before I go drilling out holes cause I know it cant be changed once done.

F-BIRD'88 04-24-2013 08:46 PM

You can weld in the O2 bung on the exhaust pipe using any mig welder or little 75amp 110v stick welder
YOURSELF. You can even read the (heated) NB O2 sensor using a DVOM.

You can test/restrict the PCV valve air flow YOURSELF. pinch the hose.
If the resulting change helps, just find a PCV valve with less flow at idle.

Hold the engine rpm at the rpm point above idle that you want to investigate.

say 1500-2000-2500 rpm Now pinch-restrict the PCV hose with pliers while watching the Voltmeter/AFR gauge
output
for the crossover voltage point .450MV rich/lean +/- crossover point.
This will show you how close you are to 14.7:1 AFR.

http://forums.pelicanparts.com/uploa...1079573429.jpg

A NB is very accurate at showing the 14.7:1 cross point. And manipulating the PCV air flow by hand while watching the gauge will show you where you are at.at various above idle rpm/throttle points.. Thats what you need to know.
is it richer than or leaner than//.Stoichiometric....?

You do not need to know the exact AFR. Off idle transition AFR leaner than say 15.5 is too lean (drivability)
richer than 12.8:1 is too rich.
Just get it close to 14.7:1. There is no ideal ratio. close to 14.7:1 is good enough thru the idle transition.
But first set the curb idle for best idle using a vacuum gauge and get the throttles position correct.
The AFR gauge will be richer than 14.7:1 at idle, when the idle is set correctly.
Play with the pri and sec throttles idle position and idle base timing .

You don't need a wide band for any of this tuning.

Same with WOT power main jet tuning. You don;t need to know the exact AFR.
You just need to know if the jet change you just made up or down in jet size made you go faster or slower.
and wether your jet changes are getting you way too lean @ WOT.
Less than .800MV @ WOT on the NB voltage. It works as a (you are way too friggin lean) warning device very well Once you learn how to use it..

F-BIRD'88 04-24-2013 09:19 PM

A NB is very accurate at showing the 14.7:1 cross point. And manipulating the PCV air flow by hand while watching the gauge will show you where you are at.at various above idle rpm/throttle points.. Thats what you need to know.
is it richer than or leaner than//.Stoichiometric....?

You do not need to know the exact AFR. Off idle transition AFR leaner than say 15.5 is too lean (drivability)
richer than 12.8:1 is too rich.
Just get it close to 14.7:1. There is no ideal ratio. close to 14.7:1 is good enough thru the idle transition.
But first set the curb idle for best idle using a vacuum gauge and get the throttles position correct.
The AFR gauge will be richer than 14.7:1 at idle, when the idle is set correctly. usually 12.5 to 13.8:1 ratio @ idle.
Idle quality and manifold vaccuum is the priority , not curb idle AFR.
Play with the pri and sec throttles idle position and idle base timing .

You don't need a wide band for any of this tuning.

Same with WOT power main jet tuning. You don;t need to know the exact AFR.
You just need to know if the jet change you just made up or down in jet size made you go faster or slower.
and wether your jet changes are getting you way too lean @ WOT.

It is a lot friggin easier to just find a different PCV valve air flow rate to correct a simple slight off idle/transiton lean spot
than to start drilling blind. You very rarely ever need to drill a carb. EVER.

Do ALL this FIRST.... You can tune the whole carb 99% using a low cost NB and a tach and a vacuum gauge
and some drive testing. You can build you own portable 12volt powered NB heated AFR gauge tool for under $100.
I did, you can too. 3 wire 4 wire NB replacement O2 sensor EG NTK 21006, summit/auto meter NB afr gauge, (or a DVOM) 4 wire trailer brake light extension wire harness with flat plug. 12v car cig lighter plug.

eric32 04-25-2013 08:17 AM

I don't own a welder and don't know how to do that but not that I can't learn. Funds to buy one is out of the option's for now. I will try some of the suggestions you posted to start off with before doing anything else such as drilling wise etc.

I am going to start off with re doing my secondary opening a little less and then re set my primary and then check the pcv valve with trial and error and then go from there. I guess I will have to start saving for a welder so I can get a 02 sensor fitting put into my exhaust.

I have seen some decent priced afr gauges at the auto part store so when funds permit I will look into buying one. I should not have to spend a ton on a welder as I have been looking at some for around 150 to 200 bucks and for something like this they would work fine. Thanks for the tips.

F-BIRD'88 04-25-2013 05:16 PM

Surely someone there has a welder. Bodyshop etc.
There are non weld band clamp style O2 bungs that only require drilling the hole in the pipe.
But the band clamp gasket included has to seal. No exhaust leaks or the AFR will be false.

eric32 04-26-2013 08:56 AM

Hello fbird I did not know that existed so thanks for the heads up and I looked on summitracing and found what I need to get for clamp wise. This will help me get in the right direction. Thanks again sir:)


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