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Holley SA 670 tweaking. Need advice.
#11
(07-13-2019, 12:17 PM)Stanglover Wrote: So today, Saturday, I took the car to the RM coffee and cars, when I got home I tackled the idle mixture one more time on a nice hot motor.
What I found was to achieve a ratio of 13.5 - 14 at idle, I needed to turn the idle mixture screws out from just seated to just 1 turn out. The more accurate vacuum gauge I bought was at 17.5"Hg. I found that turning the screws out less than 1/8th turn more, made a huge difference. The AFR would drop from around 13.5 to 12. Hard to believe how sensitive it is. After taking the car out for a blast, I noticed the idle numbers changed to around 12.5. After it cools down, I'll restart it and see if it goes back to the 13.5 area. I have decided to leave the rest of it where it is for now. With the current humidity levels, it's not "coughing" like it did, so in reality I don't think I have as serious an issue that I thought I had. The car pulls strong and fuel mileage is pretty good, so unless the problem reoccurs, it is what it is.
Besides, I need a new exhaust system before another carb anyways.
I'll go over all the advice given for reference later.
Thanks to all for your help,
Geoff.

Update; after the engine cooled down, on restart, the AFR reading was 14.2 ish. That suggest engine and carb temp play  roll in the air fuel ratio. Interesting!

Don't get caught up in chasing a number. The A/F gauge is a great tool but it is not the end all be all. Getting the car to run as well as it can within safe parameters is the goal. Seat of the pants (and/or the time slip) and how the plugs look have the final say.

73 conv. 460, D0VE large valve heads, Performer RPM manifold, Voodoo 227/233 cam, Holley 950 HP carb, C6 trans, 3.25 trak-loc.
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#12
(07-13-2019, 05:27 PM)TommyK Wrote:
(07-13-2019, 12:17 PM)Stanglover Wrote: So today, Saturday, I took the car to the RM coffee and cars, when I got home I tackled the idle mixture one more time on a nice hot motor.
What I found was to achieve a ratio of 13.5 - 14 at idle, I needed to turn the idle mixture screws out from just seated to just 1 turn out. The more accurate vacuum gauge I bought was at 17.5"Hg. I found that turning the screws out less than 1/8th turn more, made a huge difference. The AFR would drop from around 13.5 to 12. Hard to believe how sensitive it is. After taking the car out for a blast, I noticed the idle numbers changed to around 12.5. After it cools down, I'll restart it and see if it goes back to the 13.5 area. I have decided to leave the rest of it where it is for now. With the current humidity levels, it's not "coughing" like it did, so in reality I don't think I have as serious an issue that I thought I had. The car pulls strong and fuel mileage is pretty good, so unless the problem reoccurs, it is what it is.
Besides, I need a new exhaust system before another carb anyways.
I'll go over all the advice given for reference later.
Thanks to all for your help,
Geoff.

Update; after the engine cooled down, on restart, the AFR reading was 14.2 ish. That suggest engine and carb temp play  roll in the air fuel ratio. Interesting!

Don't get caught up in chasing a number. The A/F gauge is a great tool but it is not the end all be all. Getting the car to run as well as it can within safe parameters is the goal. Seat of the pants (and/or the time slip) and how the plugs look have the final say.
Tommy, yes agreed. It's more that I like playing with a new toy and to get it as good as I can. The idle mixture is of course, just that, has no effect on the overall running under power. Playing with the idle mixture is about reducing the rich idle and loosing some of the gas smell in the garage... to keep the wifey happy!
Apart from the occasional "cough" when I tramp on the gas pedal and that definitely seems to be atmospheric related as well as mechanical, I'm getting a good plug read, light brown, so I'm not worried too much about the overall performance, but more about getting a small bug out of it, i.e. the "cough".
Carbs are not my area of any sort of knowledge, but I learn something new every day..... or try to.
Thanks for the input,
Geoff.

I learn something new every day!
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