tuning with afr
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tuning with afr
So my idle is at 13.7 which isn't too terribly rich.( 20 on vacuum)
My cruise is 17.8. (6 on vacuum)
but wot is 14.8 (0 on vacuum
I have a built motor. 10:1 cr
headers Holley 600( quickfuel but whatever) dp intake and a zf5 with 36" tires and 3.55 gears.
My cruise is 17.8. (6 on vacuum)
but wot is 14.8 (0 on vacuum
I have a built motor. 10:1 cr
headers Holley 600( quickfuel but whatever) dp intake and a zf5 with 36" tires and 3.55 gears.
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From: Boise, Idaho
So...., sounds like you got your issues with the QF taken care of?? What was wrong?
13.7 isn't bad for idle. That doesn't matter so much as long as that's peak vacuum. Mine seems to like it more around 12.0:1.
Cruise: What speed is that at? Either way, 17.8 is really, really lean. 17 is probably the max I'd go. 16 is decent. 15 is getting close t running at stoich (14.7) for the best emissions. I'd look at richening up your cruise, as that is getting close to where it can cause issues/maybe damage. This can be richened up by either smaller air bleeds or a larger idle fuel restriction, or both.
WOT should be closer to 12.5 to 13. This can be richened up by bigger secondary jets, and/or larger power valve restrictions.
Glad to hear it's not dumping rich like it was before!
13.7 isn't bad for idle. That doesn't matter so much as long as that's peak vacuum. Mine seems to like it more around 12.0:1.
Cruise: What speed is that at? Either way, 17.8 is really, really lean. 17 is probably the max I'd go. 16 is decent. 15 is getting close t running at stoich (14.7) for the best emissions. I'd look at richening up your cruise, as that is getting close to where it can cause issues/maybe damage. This can be richened up by either smaller air bleeds or a larger idle fuel restriction, or both.
WOT should be closer to 12.5 to 13. This can be richened up by bigger secondary jets, and/or larger power valve restrictions.
Glad to hear it's not dumping rich like it was before!
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I took my 70 and 73 idle air bleeds and put in 76 lol. as per quick fuel.
It does backfire now. Like at a blip of the throttle it'll backfire. I stopped that real quick.
I was worried about the cruise from the get go, my old plugs, had showed signs of a lot of build up(idleing and the terribly rich idle it had) but they also had some pretty lean burn to them which had me curious about the cruise.
I just wish I'd put the wideband in a few miles ago instead of now, I wouldn't have driven it at all.
It does backfire now. Like at a blip of the throttle it'll backfire. I stopped that real quick.
I was worried about the cruise from the get go, my old plugs, had showed signs of a lot of build up(idleing and the terribly rich idle it had) but they also had some pretty lean burn to them which had me curious about the cruise.
I just wish I'd put the wideband in a few miles ago instead of now, I wouldn't have driven it at all.
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Cruise is whatever gear I happen to be in and I'm around 1000-1600 Roma. Like I said it drops my vacuum to about 5-7 partial throttle.
Idle I'm still between 18-20 which I've had the whole time and hasn't changed with my afr.
Idle I'm still between 18-20 which I've had the whole time and hasn't changed with my afr.
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From: Boise, Idaho
You may have simply gone a bit too lean on the air bleeds and need to find a happy medium. 
Or richen up the other circuits to compensate. When you start playing with the air bleeds, it all becomes a delicate balancing act.
Or richen up the other circuits to compensate. When you start playing with the air bleeds, it all becomes a delicate balancing act.
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I think I need to drop my high speed Air bleeds honestly. Because I don't remember ever seeing the 18 on cruise. I remember like 16. But I only drove a mile or two to see if maybe I could clear up 9.5 ratio. I also don't like how I have my idle adjust screws at a half turn from closed all the way around. And still am not rich enough at idle.
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From: Charlotte
Have you tried larger jets? Its my understanding that If you can screw your mixtures screws the whole way without stalling the engine then your jets may be too small. Introduce more fuel into the system then tune it down to where it needs to be.
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From: Waterloo, Iowa
I've read a quick test is that the engine should stall as idle mixture screws are turned all the way in. If it doesn't, the power valve is blown. Holley has had anti-backfire protection for quite a while now though.
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From: Spokane, WA
"...then your jets may be too small."
The main jets have nothing to do with the idle circuit. A discussion on the Speed Talk Forum several years ago brought this up and the consensus is that a carb idles perfectly well without main jets in it at all. Fuel bowl float adjustment can impact the idle though.
The main jets have nothing to do with the idle circuit. A discussion on the Speed Talk Forum several years ago brought this up and the consensus is that a carb idles perfectly well without main jets in it at all. Fuel bowl float adjustment can impact the idle though.
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From: Boise, Idaho
Agreed. Main jets also rarely have anything to do with your cruising AFR either. In lots of carbs I've worked on, my cruising AFR all way way up to 65 - 70mph was only altered by the idle fuel restriction, not the main jets, which is why I think it's just daft that they're not adjustable on most Holleys. A+ for QuickFuel on that one.
The main jets have a lot more to do with acceleration, and cruising at high RPMs.
The main jets have a lot more to do with acceleration, and cruising at high RPMs.
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I do feel like I need more fuel, however I think it's the high speed air bleeds. I don't know much about tuning fancy carbs so I can't tell you what a change in one number on the high speed will do vs a change in the idle air bleed but I'm leaning towards that.
Also I'm waiting on qft to reply to my latest email GREAT customer service.
Also I'm waiting on qft to reply to my latest email
GREAT customer service.
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From: Boise, Idaho
Carb tuning's something that you simply learn by reading, asking questions, and experimenting. You'll pick it up a little at a time.
Who knows though, may just take a couple little tweaks and it'll be just how you want it and you'll never have to touch it again.
You'll pick it up a little at a time. Who knows though, may just take a couple little tweaks and it'll be just how you want it and you'll never have to touch it again.
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told to mess with the idle screws, and not worry about the idle afr as much.
I've gotten it down to driveable, and in specs(ish) but my afr is back to 10...
Maybe I should crank it with them removed?
I've gotten it down to driveable, and in specs(ish) but my afr is back to 10...
Maybe I should crank it with them removed?
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From: Boise, Idaho
I'm not sure what you mean. What do you mean by crank it? And with what removed?
For your idle mixture screws, set the 4 idle screws to achieve the highest vacuum at idle. Don't worry too much about what the AFR is at idle. Your biggest concerns are your cruising AFR and how rich or lean your AFR goes while you're accelerating and driving.
Some days, my carb will idle at 10.5, some days at 12, some at 11. Sometimes it changes throughout the same day. Or from stop light to stop light. I've never found the idle AFR to be a very stable thing.
For your idle mixture screws, set the 4 idle screws to achieve the highest vacuum at idle. Don't worry too much about what the AFR is at idle. Your biggest concerns are your cruising AFR and how rich or lean your AFR goes while you're accelerating and driving.
Some days, my carb will idle at 10.5, some days at 12, some at 11. Sometimes it changes throughout the same day. Or from stop light to stop light. I've never found the idle AFR to be a very stable thing.
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I mean take them out and see what it goes to.
That makes me feel better about the ratio. I still want it higher. It was around 11 til I blipped the throttle then went to around 10.
Idk I think I am over thinking it. I'm going to have to tune for the vacuum. It was around 20 but now today I couldn't get it over 15..maybe it's just the weather?
That makes me feel better about the ratio. I still want it higher. It was around 11 til I blipped the throttle then went to around 10.
Idk I think I am over thinking it. I'm going to have to tune for the vacuum. It was around 20 but now today I couldn't get it over 15..maybe it's just the weather?