going lean with slight load
Thread Starter
Instructor
Joined: Feb 2005
Posts: 188
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From: Kearney Nebraska
going lean with slight load
When I set the idle mixtures screws on my holly so that it is idling at 13 to 13.5 and then go for a drive it is going lean (16 to 18) with when giving it a slight load. It I adjust all four mix screws 1/8 of a turn more open it idles at 11.5 to 12 and with a slight load it goes up to 13 to 13.5
I have the idle mixtures screw open around 1 turn. Would it help if I placed slightly larger jets in the primary? Would this allow it to idle at 13 to 13.5 without going too lean with a slight load?
I have the idle mixtures screw open around 1 turn. Would it help if I placed slightly larger jets in the primary? Would this allow it to idle at 13 to 13.5 without going too lean with a slight load?
Safety Car
Joined: Aug 2000
Posts: 3,711
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From: San Antonio TX
Maybe, but you got something going on with the carb that I don't think is going to be fixed by jets. There's no way that a small adjustment like that on the idle screws is going to give you that big of an A/F ratio swing. Idle and transition circuits contribute to main metering, but not that much.
You may be pulling air into the exhaust if you're getting those big swings. While things like the LM1 are amazing tools, they can be a bit sensitive to things like exhaust systems that aren't tight. I've also found that the tailpipe clamp is about worthless on a dual exhaust.
So, with that in mind, other than the AF meter, what leads you to believe that you're running lean?
You may be pulling air into the exhaust if you're getting those big swings. While things like the LM1 are amazing tools, they can be a bit sensitive to things like exhaust systems that aren't tight. I've also found that the tailpipe clamp is about worthless on a dual exhaust.
So, with that in mind, other than the AF meter, what leads you to believe that you're running lean?
Thread Starter
Instructor
Joined: Feb 2005
Posts: 188
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From: Kearney Nebraska
If I get the rpms up more (2500 and up) it doesn't go lean when I have the idle mixture idling around 13 to 13.5
But if I place a load load on it at 1500 rpm it shoots up lean.
PS.. I think my exhaust did have a slight leak the other day when testing. I've since fixed it but I havn't gone for a ride yet... Just finished the fix 15 minutes ago. It was leaking at the joint to the side pipe.. and the sensor is just after the joint.
But if I place a load load on it at 1500 rpm it shoots up lean.
PS.. I think my exhaust did have a slight leak the other day when testing. I've since fixed it but I havn't gone for a ride yet... Just finished the fix 15 minutes ago. It was leaking at the joint to the side pipe.. and the sensor is just after the joint.
Last edited by big69; Aug 30, 2006 at 06:01 PM.
Thread Starter
Instructor
Joined: Feb 2005
Posts: 188
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From: Kearney Nebraska
Originally Posted by gerry72
I don't care what the meter is showing you. There are very specific traits to an engine running lean. What, besides the meter, is leading you to believe you are running lean?
Thread Starter
Instructor
Joined: Feb 2005
Posts: 188
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From: Kearney Nebraska
At wot from 3000 up the a/f is around 10.5 to 11
427 Four bolt main
Crane hydraulic roller #139731, 226/234@.050, 288/296@adv., .587/.610 lift; 2,500-6,000 RPM
10:1 compression
RPM Air-Gap 2-R Intake, #75621
Holley 850 "HO-Mod" http://www.aedperformance.com/HOM.htm
MSD 6AL ignition
427 Four bolt main
Crane hydraulic roller #139731, 226/234@.050, 288/296@adv., .587/.610 lift; 2,500-6,000 RPM
10:1 compression
RPM Air-Gap 2-R Intake, #75621
Holley 850 "HO-Mod" http://www.aedperformance.com/HOM.htm
MSD 6AL ignition
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Your carb is messed up...maybe It may be the power valve, air bleeds, jets, warpage. Who knows. Even though you paid a princely sum, something is going on with the carb or your installation.
You are way too fat at WOT. And nothing else in your A/F reading or description of the problem points to a specific carb tuning issue. If it is in the carb, then you need to have a talk with the folks you bought it from. You can get better performance than that with an out of the box Holley 3310. That being said, I'd suggest that you go through the ignition before spending any more time trying to diagnose this as a carburetor issue.
You are way too fat at WOT. And nothing else in your A/F reading or description of the problem points to a specific carb tuning issue. If it is in the carb, then you need to have a talk with the folks you bought it from. You can get better performance than that with an out of the box Holley 3310. That being said, I'd suggest that you go through the ignition before spending any more time trying to diagnose this as a carburetor issue.
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
You are going to have to talk to the guys where you bought it and tell them what is going on.
What you need to get from them are all the sizes of the air bleeds, restrictors etc. THese are idle air bleed, hight speed air bleed, idle feed restrictors, power valve channel restrictor etc. etc.
NOw you can go to this site and post your problem and pray a guy named "Tuner" sees it
http://www.innovatemotorsports.com/f...isplay.php?f=7
What you need to get from them are all the sizes of the air bleeds, restrictors etc. THese are idle air bleed, hight speed air bleed, idle feed restrictors, power valve channel restrictor etc. etc.
NOw you can go to this site and post your problem and pray a guy named "Tuner" sees it
http://www.innovatemotorsports.com/f...isplay.php?f=7
Thread Starter
Instructor
Joined: Feb 2005
Posts: 188
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From: Kearney Nebraska
Just returned from a ride.
There is an off idle slump going on.
-Idle is 12.5 a/f
-slight load starting at 1500rpm it shoots to 15-16 stays there 1 second and comes down to 13
-slight load starting at 2500prm it shoots to 14 and comes down to 13
The above is worse before it is warmed up.
-larger load in 4th gear while riding the brake it shoots to 15 comes down very quick 12.5-13 and then goes back up to 15 and stays there. If I do the same without riding the brake it shoots up and then comes back to 13.5 during acceleration.
-wot from 3000 up it is around 12. I was wrong in the above post. I've since changed that jet smaller.
If I adjust the idle mixture screws to get 13.5 at idle it goes lots more lean than this.
I've changed the power valve to 1 or 2 more than the vacuum. The problem was worse before changing it.
Thanks for the help. I'll contact the AED people I bought the carb from and see what they have to say.
There is an off idle slump going on.
-Idle is 12.5 a/f
-slight load starting at 1500rpm it shoots to 15-16 stays there 1 second and comes down to 13
-slight load starting at 2500prm it shoots to 14 and comes down to 13
The above is worse before it is warmed up.
-larger load in 4th gear while riding the brake it shoots to 15 comes down very quick 12.5-13 and then goes back up to 15 and stays there. If I do the same without riding the brake it shoots up and then comes back to 13.5 during acceleration.
-wot from 3000 up it is around 12. I was wrong in the above post. I've since changed that jet smaller.
If I adjust the idle mixture screws to get 13.5 at idle it goes lots more lean than this.
I've changed the power valve to 1 or 2 more than the vacuum. The problem was worse before changing it.
Thanks for the help. I'll contact the AED people I bought the carb from and see what they have to say.
Last edited by big69; Aug 30, 2006 at 08:47 PM.
Drifting
Joined: Sep 2004
Posts: 1,959
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From: North Bend Ohio
The mixture going lean at throttle application is a fault with the accelerator pump. I would advise you to disconnect the secondaries and tune the primaries alone. When you have the primaries sorted out then reconnect the secondaries.
Part throttle cruise is done on the main jets. The power valve should be set 2 inches below cruise vacuum. The power circuit is tuned with the power valve restriction.
BigBlockk
Later.....
Part throttle cruise is done on the main jets. The power valve should be set 2 inches below cruise vacuum. The power circuit is tuned with the power valve restriction.
BigBlockk
Later.....
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
It very well could be a primary pump problem. CHeck to make sure you are getting a pump shot as soon as the throttle position is advanced. YOu can check this a idle, look down at the primary shooter and give it a bit of gas and see if you see a small stream of gas coming out of the shooter nozzles, as soon as you move the throttle you should see the gas coming out. If it is late or not coming out at all or it is clogged then that's your lean spike 