lean condition
Thread Starter
Racer
Joined: Dec 2004
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From: crystal lake Il.
lean condition
I just got back from a dyno run. Not bad 275 horse and 310 tq. The problem is I have a severe lean condition from icle to 3100 rpm then it gets right where its supposed to. I have a holley 670 street avenger. how do you richen up the lower end?
Le Mans Master
Joined: Jun 2008
Posts: 5,284
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From: Rockledge FL
i am not an expert on holleys but chances are your primaries are a little small and then when the secondaries kick in the extra fuel from the back jets fatten it up a little.
id go up a size or two on the front
id go up a size or two on the front
Pro
Joined: Jun 2004
Posts: 700
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From: Lantana TX
I dont want to cost you more money, but you may want to look at an LM1 AFR unit. I have one and do a tremendous amout of tuning without being on the dyno every other week.
food for thought..
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Your dyno run started at idle ?
From my experience they will start the run at 2300-2500RPM at which point many motors will go lean momentarily then pull down to where they should be, are you sure this is not what is happening ? Do you have a printout of the dyno run ?
From my experience they will start the run at 2300-2500RPM at which point many motors will go lean momentarily then pull down to where they should be, are you sure this is not what is happening ? Do you have a printout of the dyno run ?
Race Director
Joined: Oct 2000
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From: central FL, near the beach.
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Thread Starter
Racer
Joined: Dec 2004
Posts: 336
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From: crystal lake Il.
The dyno run started at 2300, the af was at 17.3, went down to 16.8 then went up past 18 until 3100 then came down to 12.4. At idle the af ratio was reading 18. The idle screws seem to be adjusted right. I had a vacuum gauge on it. I got 13 hg of vacuum, Is that low? I`ve got a lunati 103 cam, 227/233 @50 110 lsa. Would a bad power valve cause this?
Race Director
Joined: Oct 2000
Posts: 14,955
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From: central FL, near the beach.
670 street avenger? is that a vacuum secondary carb? maybe the spring is too light and it opens before the fuel will flow. that is way more likely than a froze up PV.
Just give it 1/2 throttle until 3100, then floor it. That's what old guys did before LM-1's and big tuning budgets.
Just give it 1/2 throttle until 3100, then floor it. That's what old guys did before LM-1's and big tuning budgets.
Last edited by Matt Gruber; Aug 23, 2009 at 08:49 AM.
Thread Starter
Racer
Joined: Dec 2004
Posts: 336
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From: crystal lake Il.
It is a vacuum secondary and I do have a very light spring. The power valve moves back and forth so it seems to be good. It just isn`t gettihg enough fuel until just over 3000 rpm. You can really feel it, like a turbo kicks in at 31-3200 rpm. Is it normal to be that lean at idle?
Race Director
Joined: Oct 2000
Posts: 14,955
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From: central FL, near the beach.
if u drive it like i said, it will out-accelerate a stock heavy spring.
18:1 idle? usually it would stall too easy, but if it runs fine, it would use less gas idling in traffic. Good!
But, if it is so lean that it overheats; then u have to richen it or boil over
18:1 idle? usually it would stall too easy, but if it runs fine, it would use less gas idling in traffic. Good!
But, if it is so lean that it overheats; then u have to richen it or boil over
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
First you need to tune it at idle with the idle mixture screws to get 14:1 or thereabouts ( my 427 small block likes 13.5:1 ). That is the reason you are seeing such high readings at ~2000RPM it is still running on mostly on idle and transfer circuits.
Then when you punch the gas your power valve opens and now you are running on main circuit, the power valve circuit and the accelerator pump circuit. It is common for a slight lean condition as these circuits kick in but this is not your problem.
Your problem is you are way to lean at idle
Then when you punch the gas your power valve opens and now you are running on main circuit, the power valve circuit and the accelerator pump circuit. It is common for a slight lean condition as these circuits kick in but this is not your problem.
Your problem is you are way to lean at idle
Race Director
Joined: Oct 2000
Posts: 14,955
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From: central FL, near the beach.
when u floor it any carb will flow thru the main jets, and as vacuum approaches zero, the idle circuit will flow ZERO. NADA. NOTHING. Without the pump shot taking up the slack it will stall/backfire.
If u r gently accelerating, maintaining good vacuum, idle will flow, and if the car goes to 18:1 and stumbles, idle is too lean.
O2 sensors sometimes get confused at idle with a high overlap cam like you have, so any weird reading needs to be backed up with symptoms
If u r gently accelerating, maintaining good vacuum, idle will flow, and if the car goes to 18:1 and stumbles, idle is too lean.
O2 sensors sometimes get confused at idle with a high overlap cam like you have, so any weird reading needs to be backed up with symptoms
Last edited by Matt Gruber; Aug 23, 2009 at 01:00 PM.
Race Director
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Knew someone was going argue. Are you saying the power valve circuit is not being used ? Take a look at the diagram below, if it is wrong let me know. I have spent allot of time trying to get this right with the help of the LM-1 wideband and Innovate forum.
Last edited by MotorHead; Aug 23, 2009 at 01:02 PM.
Race Director
Joined: Oct 2000
Posts: 14,955
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From: central FL, near the beach.
DO NOT START(engine off is zero vacuum)
open throttle if it pleases you
look down into intake manifold
is fuel flowing(other than pump shot)? Is there fuel in bowl? Why isn't it flowing?
Yes, chart is wrong.
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
You still haven't mentioned the power valve circuit, I find that interesting that your carbs don't need that circuit.
I happen to disagree somewhat with your assessment of how a carb works so let's leave it at
I happen to disagree somewhat with your assessment of how a carb works so let's leave it at
Race Director
Joined: Oct 2000
Posts: 14,955
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From: central FL, near the beach.
this is not an argument 
carbs are complex; i enjoy solving a puzzle; i'm wrong sometimes, thats why i do the tests.
I'm perplexed that u think the PV has anything to do with a normal 500-900 rpm idle in neutral.
The TEST is to put a temporary PV plug in your carb and see if it changes the idle. Or u could tie the pv open. It won't do anything either way, but u may have to do the test to believe it
And since i don't know anything about your set-up, i could be wrong. 
Then i can learn something new.
carbs are complex; i enjoy solving a puzzle; i'm wrong sometimes, thats why i do the tests.
I'm perplexed that u think the PV has anything to do with a normal 500-900 rpm idle in neutral.
The TEST is to put a temporary PV plug in your carb and see if it changes the idle. Or u could tie the pv open. It won't do anything either way, but u may have to do the test to believe it
And since i don't know anything about your set-up, i could be wrong. Then i can learn something new.
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I don't see where I said the PV is doing anything until the vacuum goes below where it is rated. 
Anyway, I am not here to win arguments. I am here to try and help fellow forum members fix their problems and also get my own problems fixed. Been doing this for almost 10 years now, winning arguments is for kids.
If I disagree with someone, this is not a hostile situation, merely two different ideas on how something works. This is also how one learns things.
Anyway, I am not here to win arguments. I am here to try and help fellow forum members fix their problems and also get my own problems fixed. Been doing this for almost 10 years now, winning arguments is for kids.
If I disagree with someone, this is not a hostile situation, merely two different ideas on how something works. This is also how one learns things.
Race Director
Joined: Oct 2000
Posts: 14,955
Likes: 79
From: central FL, near the beach.
well
at idle if u lower the idle speed until vacuum is below the PV rating, the PV will open, but no extra fuel flows; not in my holley 4165 by actual test.
Only a guy with the "idle" so high that the main booster is flowing will get more fuel. That's not idle in my book.
Anyway,
painter52 should buy the specific carb book for his carb and study it. there are different features/functions
at idle if u lower the idle speed until vacuum is below the PV rating, the PV will open, but no extra fuel flows; not in my holley 4165 by actual test.
Only a guy with the "idle" so high that the main booster is flowing will get more fuel. That's not idle in my book.
Anyway,
painter52 should buy the specific carb book for his carb and study it. there are different features/functions