QUOTE(forrestkhaag @ Oct 10 2017, 11:04 PM) 
Idle jets (60) made a big diff as well as timing advance.
It has been said that many carburetor issues were ignition related.
Full Version: 10 MPG!
Idle jets (60) made a big diff as well as timing advance.
It has been said that many carburetor issues were ignition related.
QUOTE(billium01 @ Oct 8 2017, 02:29 PM)
Aviation engines that are air cooled run rich to help keep them cool. Is that something they do with air cooled Porsche engines?
Does running rich actually help keep aviation engines cool, or is it more to resist detonation when the engine is running hot?
Yep Billy that mpg seems about right, you might be able to lean out the cruise afr some, dial in max timing advance and get it a little better.
With my webber 40's and my 3.0 I could get 23 mpg of straight freeway driving at ~75-80. I never measured track, but I imagine it would be in the 8-10 range. My typical cruising around the city flogging it here and there mpg I believe was around 12-15. With my now 3.2 and pmo 46's I average around ~10mpg all the time but its all around town spirited driving.
The main fault of the carbs is at cruising speed ~3k rpms they run rich ~12:1 afr, there is no way around it. Most fuel injected cars are near 14.7:1, that's a 20% increase. But with the throttle down they are all ~12 afr for max power and the more power you make the more fuel you consume...
Also it doesn't apply to Webber or PMO carbs, but vacuum advance on timing does make a big difference for part throttle. You can do this on Webber or PMO's, but you need to tap each intake with a vacuum port and make a common vacuum manifold, so that its consistently pulling vacuum to the distributor. I've never seen anyone do this, but it can be done.
With my webber 40's and my 3.0 I could get 23 mpg of straight freeway driving at ~75-80. I never measured track, but I imagine it would be in the 8-10 range. My typical cruising around the city flogging it here and there mpg I believe was around 12-15. With my now 3.2 and pmo 46's I average around ~10mpg all the time but its all around town spirited driving.
The main fault of the carbs is at cruising speed ~3k rpms they run rich ~12:1 afr, there is no way around it. Most fuel injected cars are near 14.7:1, that's a 20% increase. But with the throttle down they are all ~12 afr for max power and the more power you make the more fuel you consume...
Also it doesn't apply to Webber or PMO carbs, but vacuum advance on timing does make a big difference for part throttle. You can do this on Webber or PMO's, but you need to tap each intake with a vacuum port and make a common vacuum manifold, so that its consistently pulling vacuum to the distributor. I've never seen anyone do this, but it can be done.
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