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Old 07-22-2008, 02:50 PM
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adjusting from sea level to 4000ft elevation

I just got my 72 el camino with a 350 in it all set to drive on the street except for tuning the carb and timing. It was running perfect at sea level when I bought it but I had to assemble part of the body and misc engine parts that were removed.
I moved from sea level to 4000ft level and I know I need to go down 2-3 jet sizes. Do I need to retard the timing too? I want to use this as an everyday driver and will b going from 4000ft down to about 1000 ft every day.

The Idle seems perfect and it seems to run real good, but if i get on the throttle quickly( like jump from 600rpm up to like 1000) when it comes down from the rpm it acts like it wants to die, or even some times does die. Is that a specific problem?

I know how to adjust the distributer if I need to only adjust it a few degrees. the jets I know how to change as well but im not good at readjusting the 4 corner idleing screws and so furth.
Any info would be appreciated.

thanx
david

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Old 07-22-2008, 03:23 PM
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Quote:
Originally Posted by daveid
I just got my 72 el camino with a 350 in it all set to drive on the street except for tuning the carb and timing. It was running perfect at sea level when I bought it but I had to assemble part of the body and misc engine parts that were removed.
I moved from sea level to 4000ft level and I know I need to go down 2-3 jet sizes. Do I need to retard the timing too? I want to use this as an everyday driver and will b going from 4000ft down to about 1000 ft every day.

The Idle seems perfect and it seems to run real good, but if i get on the throttle quickly( like jump from 600rpm up to like 1000) when it comes down from the rpm it acts like it wants to die, or even some times does die. Is that a specific problem?

I know how to adjust the distributer if I need to only adjust it a few degrees. the jets I know how to change as well but im not good at readjusting the 4 corner idleing screws and so furth.
Any info would be appreciated.

thanx
david
You add timing with altitude. The reason for this is mixture density (atoms of air per trapped volume) is less. This slows the burn rate, especially toward closed idle throttle settings. The solution is to just kick up the base timing a about 3 to 5 degrees. If you lived higher or weren't seeing these daily altitude changes, you could lean out main metering a little, but I'm not so sure the result is worth the effort in your case.

Bogie
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Old 07-22-2008, 03:44 PM
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so dont even worry about the jetting and just bump the timing 3-5 degrees?
Is the timing the issue of why when I rev it, coming off the rev it dies or tries to die? If im to try and drive it in drive it almost acts like a clutch and keeps dieing unless i get on the brake and rev it up a little and then it will go and not die.

thanx
david
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Old 07-22-2008, 04:13 PM
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Originally Posted by daveid
so dont even worry about the jetting and just bump the timing 3-5 degrees?
Is the timing the issue of why when I rev it, coming off the rev it dies or tries to die? If im to try and drive it in drive it almost acts like a clutch and keeps dieing unless i get on the brake and rev it up a little and then it will go and not die.

thanx
david
You'll find that adding some base timing will speed up the idle. It's try to die because the snapping the throttle closed causes the mixture to fall momentarily rich. It's a combination of inertial in the fuel and low air density. The fuel flow briefly over runs while the air density falls off quickly. enlarging the idle air correction jets could help. But bumping the timing up a bit should also cover this.

I'm not saying that you'll not want to change jetting, just start with the base advance see how it likes it. Then you can refine the jet settings if you want to dial it in tighter. Also, if you're not using an HEI ignition or other type of electronic ignition, you'll find that a hotter spark or in the case of multiple sparks like MSD should also help the idle response.

Bogie
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Old 07-22-2008, 05:06 PM
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You'll definetly have to drop the jets down or it will be so rich it will look like a diesel out the exhaust. If you stay at that altitude mostly, you can tailor it as required, but your initial drop is about right. If you intend to go to lower altitudes, you might want to keep the jets you remove for then. If you will be doing it often or regularly, you mnay want to look into and adjustable jet plate that you can just tweak back and forth.I took a Mach I through Colorado in '78 right after i rebuilt it and hadn't had time to jet the Holley for our area. It was a little rich, but since I was breaking it in, I didn't mind....MAN...when we started getting up there I had to pull over and buy a handful of various size jets and jetted it about every 5 miles until it felt good( gas mileage inproved drasticly also,LOL). I think I went down 4-6 sizes, so your initial estimate should be a good if not great start.
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Old 07-22-2008, 10:00 PM
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ok I brought up the timing 4 degrees to 12. Is this around where the timing should be? I know it would probly be best to go to a tech and just have them do it but I did that with my last car and I really want to learn how to and why. It seems to sound a little better and I had to raise the idle a little. I still havent jetted it down yet. It smells rich but exhuast has no smoke so Ill probly jet it down a few.
I am planning on driving down to around 1000ft altitude everytime I drive it and if I dont then my trips would only be about 5-10 mins long when im only at 4000ft altitude.

Now to and another problem or add another equation to the problem, My fan comes on at 160 degrees. About 10 seconds after it comes on is when the car dies. any suggestions?

Thank you guys for staying with me here.
david
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