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  #1 (permalink)  
Old 11-20-2022, 07:11 AM
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Join Date: Feb 2021
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Cobra Make, Engine: Factory 5 Daytona Coupe, 347 SBF Stroker 48ida Webers
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Default Jetting for 48IDA Moving from Sea Level to Mile High.

Hey all, new to the Forum.

I've just moved my father's FFR Daytona Coupe from Alaska to Denver to get it some track time; it should arrive here by December. It has a Jim Inglese 8 stack 48IDA webers on it's SBF 347 stroker. My dad never got it running quite right at sea level, it had major back firing issues. I suspect because of fuel pressure problems but I need to look more into it.

Anyway, I will obviously have to change jets to accommodate the altitude. Anybody have a recommendation on where to get a jet kit, or do I just have to buy them individually? Anybody have experience of jet changes from sea level to high altitude?

Any help is appreciated.

Cheers.
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Old 11-20-2022, 08:10 AM
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Generally speaking, you need to go down about 2 jet sizes. That varies by engine build, though.

Sometimes, backfiring is caused by a lean mixture. So you might need to go down 1 or 0 jet sizes.

Check all the other issues that can cause a back fire first. Once those are fixed, then starting adjusting mixture.

Don't guess. Spend the money on a sensor and actually measure mixture before making changes. Otherwise, it's very easy to go from bad to worse.

ITB are extremely sensitive to balance. If the balance is not perfect, no amount of tuning will make it run well. Buy a synchronometer.
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  #3 (permalink)  
Old 11-20-2022, 11:19 AM
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I suspect it is running real lean. Got a synchometer ready. I have been waffling on whether or not to install an AFR Gauge, The way the headers an pipes are set up Ill only be able to read the O2 on one Carb. Might be worth it though since I can just assume the others will be exactly that same. Anybody have a similar setup?
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Old 11-20-2022, 02:01 PM
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Backfiring can be caused by either rich or lean. My experience is rich dominates but it can be either. An O2 sensor reading will tell you which. But lean backfiring is often associated with low fuel pressure so it's a good place to start especially if you suspect that.
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Old 11-20-2022, 02:04 PM
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You can place the sensor up into the tailpipe, and measure one side or both sides at the same time. Not sure about 4, though.
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Old 11-20-2022, 02:49 PM
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I'd get one of the weber suction things and make sure it's balanced before hooking up sensors. Webers is an art and more an issue of patience. Maybe you'll have better lock finding someone in Colorado to tune it up.
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Old 11-24-2022, 07:06 PM
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Tuning without an O2 sensor is almost impossible. Get a welder to weld in an O2 sensor in your collectors so you can go out and drive the car and see where the engine is rich and lean.

https://www.summitracing.com/search?...%20weld%20bung
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