Got a quick query. How much effect does timing have on oxygen content?
>I'm trying to dial in an engine and am using an O2 sensor. It's a small
>block Chevy V8 and the sensor reads rich, which is very much what I'd
>expected re: rich smell, fouled plugs, atrocious mileage. The engine's new
>and the carb's used but in excellent (visual) condition.
> The carb's a 650cfm double pump Holley that's in very new condition (used
>but still in original box) but got it from my machinist who drag races. The
>jets indicate stock but who knows if somebody drilled them. The
>distributor's a Mallory Comp 9000 and at this point who knows what the spark
>curve's set to.
> So, as I try to dial in the spark curve and fuel, I'm wondering, "Can the
>timing curve significantly change O2? Am I trying to dial in the wrong >system first?"
> Best Regards,
> Drink
>
Timing should have little effect on oxygen content. The oxygen content is determined by the fuel - air ratio going into the cylinders and that is controlled by the carb. Maybe re-jet it to be sure you have stock jets, then start adjusting the mixture screws.
If the carb was used on any sort of a "drag" motor... then it probably has the wrong power valve in it (or the power valve is damaged); and the power valve is opening during part throttle cruise. There's a description of how the power valve works here:
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"See if this description sounds familiar: Your Holley-carbureted street car idles terribly, has taken to fouling spark plugs every week or so, the gas mileage absolutely sucks, and there's an ominous black cloud swirling from your exhaust."
I think you're supposed to select a power valve that's rated about 2" HG lower than whatever your part throttle cruising vacuum reading is:
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"Tom S" wrote in message news: snipped-for-privacy@4ax.com...> On Sat, 27 Jan 2007 18:57:02 -0600, "James Drinkwater"> wrote:
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