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Join Date: Jul 2006
Location: Charlotte, NC
Posts: 1,964
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Carb accelorator pump question
I've been having some issues with cold starts. Been doing 3 or 4 "full" pumps, crack the throttle a bit, attempt to start. Takes 3 or 4 attempts if the car has sat for a few days.
Today I thought, turn the key on to start the pump, and 3 full pumps BACK AT THE CARBS. Car started right up this time. I had someone sit it the car and fully press the gas peddle and I'm short of WOT. Accel pump is just kicking in essentially. I would imagine this would effect cold start?? Not getting a full shot of gas? I also have an issue where stepping on it @ 3k rpm gives some hesitation. I imagine this could also be related to partial accel pump? At any rate, I need to adjust my linkage. Not an easy task solo :-(. Todd
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'81 SC |
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06-05-2014, 11:25 AM
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Join Date: Jan 2006
Location: Santa Barbara, CA
Posts: 2,307
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Assume you are talking about Webers?
Not getting WOT is a problem. Not sure why it has anything to do with any of your other problems. If accelerator pump isn't delivering enough gas, you don't need to adjust it, just give pedal a couple more pumps. You'll have more gas. 3k hesitation may be directly affected by the accelerator pump volume. Turn the adjustment nuts in or out 10 turns or so on both sides and see what happens. If hesitation is worse, go back to where you were and past it a few turns in the other direction. If better, turn a few more turns in the same direction. It's always useful to run the fuel pump for a few seconds before you try to start a carb'd car.
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jhtaylor santa barbara 74 911 coupe. 2.7 motor by Schneider Auto Santa Barbara. Case blueprinted, shuffle-pinned, boat-tailed by Competition Engineering. Elgin mod-S cams. J&E 9.5's. PMO's. 73 Targa (gone but not forgotten) |
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06-05-2014, 02:01 PM
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Join Date: Feb 2008
Posts: 1,438
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Have a read of this link to help understand accelerator pump operation and details of adjustment: Weber accelerator pump linkage help please
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Paul Abbott Weber service specialist www.PerformanceOriented.com |
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06-05-2014, 03:00 PM
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Under the radar
Join Date: May 2007
Location: Fortuna, CA. On the Lost Coast near the Emerald Triangle
Posts: 7,129
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There is a procedure for measuring the accelerator pump discharge in each port. You might want to start there. Should be something like .7mm per squirt.
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Gordon ___________________________________ '71 911 Coupe 3,0L outlawed #56 PCA Redwood Region, GGR, NASA, Speed SF Trackrash's Garage :: My Garage |
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06-05-2014, 06:49 PM
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Recently I went through a similar issue after my car sat idle for awhile, somehow I had got some crud in the jets and acceleration jets, easy to clean out, now all is good.
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78’ SC 911 Targa - 3.2SS, PMO 46, M&K 2/2 1 5/8” HEADERS, 123 DIST, PORTERFIELD R4-S PADS, KR75 CAMS, REBEL RACING BUSHINGS, KONI CLASSICS |
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06-05-2014, 07:23 PM
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Join Date: Jul 2006
Location: Charlotte, NC
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Yes, I still need to get/set the volume (maybe it will be spot on). I guess my point was if I'm not going full WOT, then I'm not getting a full shot from the pump I'm sure, so regardless of the setting I'm going to be low.
I adjust my pedal linkage a bit and drove the car tonight. Still not sure if I'm WOT (lost my helper), but there is a half second pause (think Paul discusses this in his link above), and then it snaps your head back. Think I'm close :-) Todd
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'81 SC |
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06-05-2014, 07:30 PM
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My Garage
1971 Porsche 911
Baja Bug
Stella
