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Registered
Join Date: Nov 2008
Posts: 2
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Newb posting about fuel pressure level for webbers...
hi everyone...first post here about my new (old) 1980 SC with webber carbs. one of the many problems that im facing currently is that i get HORRIBLE gas mileage...like 11 or 12 mpg tops. Ive done multiple tests and it always gets about that. I see that at idle, the pressure gauge reads about 8...and im pretty sure thats a little high for webers. It looks as if though there is some gas spraying out of the carbs too, but i cant tell for sure.
I notice that the car backfires some too. The Porsche shop i go to (powertech) had them set up and tuned for me, and thats what they set them at. Should i lower the pressure on them? if so, to what? Last edited by backroomstudios; 11-06-2008 at 09:57 PM.. |
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11-06-2008, 04:52 PM
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Registered
Join Date: Sep 2008
Location: Rio Rancho, New Mexico
Posts: 200
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Weber fuel pressure is 3.5 psi.
There is likely other issues for your lower than normal mileage. Are the carbs 40's or 46's? I would expect 46's to lower your mileage. Venturi size will greatly affect mileage and performance. 34mm with 40's should return decent mileage. 32mm will return better mileage at the expense of the top end performance. Basically if the car is set up for performance, the mileage can suffer. The transaxle axle ratio, specifically running a 7:31 ring and pinion vs the stock 8:32 will improve low end performance while using more fuel. Performance cams generally reduce mileage as well. The carbs will not match the mileage of the fuel injection with out reducing performance. Typically adding carbs is accompanied with hotter cams, higher compression pistons and free flowing exhaust. All of these mods get more air/fuel into the engine adding to the fuel used. I'd check back with Powertech, they will have some answers for you.
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Doug Was 2.7racer. '76, 2.7 w/Webers, JE pistons, Solex cams. Elephant bushings front & rear, 23mm & 28mm torsion bars, big brakes front & rear, Pertronix. Track car. '85 3.2 stock, Orient red, comfy street car. |
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11-06-2008, 07:34 PM
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Registered
Join Date: Nov 2008
Posts: 2
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thanks so much. I love to annoy the guys over at powertech, so i will bug them about this. Is it hard to reduce fuel pressure, or just a quick adjustment?
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11-06-2008, 09:58 PM
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AutoBahned
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if you keep the CIS pump -- and you should -- you buy a PMO recirc. valve unit - it has a gauge on top - $45
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11-07-2008, 10:41 AM
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