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Old 07-18-2008, 03:16 PM
oldbogie oldbogie is offline
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Quote:
Originally Posted by dh79
When I say cruise I mean 3000 rpm on the freeway (100 km/hr). At that point I'm pretty sure I'm on the primary main jets.

I'm using this wideband as another tuning tool in the toolbox. I'll be taking it to the track soon, but I'd like to get my wot down to 12.5-13 first, and experiment from there.

I've been using the wideband and vacuum gauge to set the idle mixture. I think it's nailed down pretty well now. I'm amazed how such a small change in the mixture screws affects the afr.

When are the extended secondary jets recommended? Last time at the track it ran 12.6, but I think low 12's are realistic. It 60' 1.74 last time. Any idea what the air/fuel datalog will look like when the secondary jets go dry? I guess it would lean out for a while, then come back?

thanks for the help,
dh
You used a term that got my attention which is "secondary jets go dry"! If the jets were to go dry you'd have a serious leaning of the mixture, either a top end back fire and or detonation would be the first indicators, roasted pistons would be next. The Holley (actually any carb in drag racing) does have a situation from vehicle dynamics where the fuel rushes toward the primary jets and away from the secondary jets. The secondary jets typically being larger will show a greater amount of leaning than the smaller primaries will show richening. This is where jet extensions can be of help, especially on the secondaries because the fuel rushing away from the jets can cause a severe lean drop in the mixture. With jet extensions it keeps the jet connected with the pool of fuel now at the rear of the float bowl. On the primary side I like a bit shorter jet extension to average out the depth of fuel that is now a puddle against the metering block, although, I'm a lot less concerned about the primary side as possible engine destruction isn't an issue here, this is just a tuning issue to keep the mixture in a tight range around what works best for the engine.

Bogie
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