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Idle low throttle miss - stock 914-6
I'm trying to tune a 1970 2.0 with webers and have an idle miss that I've not been able to tune out. The car runs strong under acceleration but has a miss at idle and under light throttle (maintaining speed). I've changed points set dwell replace plugs wires cap rotor, sync'd carbs several times. The car was at a well known local shop and they were unable to fix and after 5 months I took the car back. They didn't get much done so I have no idea how much time they put on it. Idle jets are 50s. Carbs are clean fresh rebuild. Any ideas or troubleshooting techniques would be greatly appreciated. Thanks. I can shoot some video tomorrow.
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11-16-2013, 04:27 PM
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Additional info - at idle the car sounds like its missing one or two cylinders. Little hesitation with throttle and then it's like a switch and all 6 cylinders hit and the car accelerates hard right through the rpm range. Running through the gears it sounds great.
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11-16-2013, 04:47 PM
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Join Date: Jul 2001
Location: Portland Oregon
Posts: 7,007
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Make sure your ignition system is in PERFECT condition before touching carbs.
This means checking the resistance of all plug wires & connectors as well as confirming dwell & timing. Cap, rotor, and plugs must be in perfect shape. After that, make sure your valve adjustment is spot on. Check for any vacuum leaks at the throttle shafts, intake manifolds (both top & bottom) before proceeding since any tiny vacuum leak wreaks havoc with trying to set AFR's at idle and light load. Rule of Thumb: never, ever assume anything.
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Steve Weiner Rennsport Systems Portland Oregon (503) 244-0990 porsche@rennsportsystems.com www.rennsportsystems.com |
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11-16-2013, 10:08 PM
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Join Date: Aug 2010
Location: Küsten, Germany
Posts: 175
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What Steve said.
Plus: Synchronisation of the carbs best done by vac. guages you apply BELOW the throttles, which compensates also potential vac. leaks and help best for a proper air adjustment: Scheuerlein Motorentechnik - Boehm Synchrontester mit 6 Uhren - Scheuerlein Motorentechnik |
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11-17-2013, 03:56 AM
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Thanks guys. I did read a post regarding a distributor that was worn and causing a miss on two cylinders. Will double check timing and check the new wire resistance. Dwell is 37 degrees. Have a spare distributor that I can swap if I need to.
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11-17-2013, 05:36 AM
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Join Date: Feb 2008
Location: Phoenix Arizona
Posts: 166
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The leading cause for a low end miss that clears up at higher revs is dirt in the idle circuit. Remove the idle jets at the top of the carbs and blow air thru them...Bear in mine there are a LOT of possibilities---but it has gotten to the point that with any Weber carbed 911 with a miss I clean the idle jets first because it is easy---
aws |
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11-17-2013, 07:11 PM
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Registered User
Join Date: Jan 2011
Location: Oregon
Posts: 6
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Distr.
Hi... I'm sorta going through the same senario with my 914-6.... I was curious what type/# distr is installed on your -6.... mine is a 008
Thx M |
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12-11-2013, 06:51 PM
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Join Date: Mar 1999
Location: Des Plaines, IL USA
Posts: 79
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If the carbs are original, you might consider having them rebuilt as they're all getting very old and starting to have issues with bushings and other parts simply wearing out. Not cheap, but it's been 40 some years ago that they were originally built. Also, I highly agree that you need to clean out the idle jets.
However, before spending that money, I do agree that most carb problems are in the ignition system! |
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12-16-2013, 11:17 AM
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