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73 Sporto 911T-V RoW
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Idle jet sizing
Hi,
I've read a few threads on modification that were done to the carbs and was wondering if someone can help. On the Zenith 40 tin carbs I took the advice to remove the enrichment circuit therefore everything is plugged with no leaks but this naturally causes a lean mixture throughout the whole throttle range. The Idle jets are 47.5 and have no choice to increase the size because of the missing fuel that came from the enrichment circuit. The enrichment jet are 50 therefore calculating the surface area of both idle and enrichment jet I get a value "A". Example: Idle jet 47.5 = 0.7085 mm sq Enrich jet 50 = 0.7850 mm sq Total = 1.4935 mm sq Could I assume that I can calculate the surface area of the new idle jet to equal that "A" value? 60 = 1.1304 mm sq 65 = 1.3260 mm sq 70 = 1.5386 mm sq At 50$ a set of 6 I would like to avoid spending too much for trying out which one works. ![]()
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Daniel ![]() |
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Registered
Join Date: Mar 2001
Location: Marysville Wa.
Posts: 22,442
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take a 0.55 jet drill to the 47.5 idle jets. good starting point.
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https://www.instagram.com/johnwalker8704 8009 103rd pl ne Marysville Wa 98270 206 637 4071 |
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73 Sporto 911T-V RoW
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Thanks John,
I remember a while back I used "Butterfield" bits that were of good quality. Would you have any recommendations?
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Daniel ![]() |
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Join Date: Feb 2008
Posts: 1,438
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The enrichment circuit is off during acceleration and constant throttle applications so there is no contribution to fuel mixture when working.
52 to 55 idle jets are good to go with per John Walker's recommendations.
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Paul Abbott Weber service specialist www.PerformanceOriented.com |
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73 Sporto 911T-V RoW
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Quote:
Thanks
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Daniel ![]() |
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