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Registered User
Join Date: Sep 2012
Posts: 5
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71 911T Hesitation between 4000-5000rpm
At about 3000 rpm starts to stutter up to 4000. Has Weber carbs and MSD Ignition. Was wondering if it could be Accelerator pumps on carbs? any ideas? Much Appreciated
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07-11-2015, 07:03 PM
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Registered User
Join Date: Jul 2015
Posts: 4
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Double-check that the distributor isn't 180 degrees from where it should be.
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07-12-2015, 07:45 AM
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Join Date: Feb 2008
Posts: 1,438
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Stock 2.2T? Do you know what the venturis size is & jetting as installed? Did this just start occurring or is this a new installation of Webers? Did you rebuild them? Have the float levels been set using the vial and allowed to settle while the engine is running? Were the air flows balanced both cylinder to cylinder at idle AND side-to-side @ 3000RPM? Distributor timing checked @ 6000RPM and advance operating smoothly?
The 4000 to 5000 region is mostly main circuit contribution, a little idle/progression fuel circuit is still active at 4000 but not much. Stutter indicates lean mixture. Could be a side-to-side air flow imbalance, this would have one side advanced over the other. Larger throttle openings would minimize the flow imbalance. Best guess without further info to consider.
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Paul Abbott Weber service specialist www.PerformanceOriented.com |
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07-12-2015, 07:59 AM
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Registered
Join Date: Jan 2006
Location: Clayton NC
Posts: 1,674
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clinejens, you are new to this forum. Mr. Abbott is the guru where weber's are concerned. Answer his questions then implement his answers and all will be well in your weber world.
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gary 70T coupe forever almost done 88 Carrera Targa diamond blue |
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07-12-2015, 08:31 AM
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Join Date: Sep 2012
Posts: 5
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Paul,
Its a 2.2 with a big bore kit making it a 2.5 with 2.7 crank and S cams. I don't know the ventures size or jet size, but I can tell you that tuning the carbs has become unmanageable. Over the years the car does not get driven that much maybe 4-5 times a year, I am at altitude but nothing has changed over the 10+ yrs in ventures or jetting. I am thinking that maybe the carbs need a good overhaul. What are your thoughts? Thanks, Jens |
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07-12-2015, 09:50 AM
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Join Date: Feb 2008
Posts: 1,438
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Well, a good cleaning & tuning would help narrow the number of possibilities for troubles. The stumble is in an odd portion of the fuel delivery circuit to become lean (assumption that it is lean based upon the stuttering). Possibly some garbage has entered the system and a good cleaning would sort the issue.
Can you clarify "unmanageable"?
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Paul Abbott Weber service specialist www.PerformanceOriented.com |
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07-12-2015, 11:27 AM
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