<VV> 140 timing (with 280 isky cam) and 4 primary carb tuning advice wanted

[Sethracer at aol.com]

In a message dated 11/25/2009 8:52:36 P.M. Pacific Standard Time,  
62vair at gmail.com writes:

Ray, I  believe that the carbs are set up so the secondaries come in at
around 25%  of the primaries (built into the linkage). I read an article a
week or so  ago that talked about people adding the second set of carbs to a
two carb  engine from back in the 60's, and they used 4 primaries, but the
second set  too was set to phase in at around 25 %, for driveability, it
says. Clarks  has a kit to do just this,and their  material says the same
thing. I  assume the original 140 setup is the same.
Mark  Durham


With some judicious measuring and a bit calculating you can measure the  
opening ratio of the secondary carbs. But the most important thing is to make  
sure that, when the pedal is on the floor, with your hands off of the  
cross-shaft, all four carbs are fully open.  Adjusting the clevis/pin on  the 
shaft up from the trans will allow you to force the primaries open, but you  
will likely have to play with the secondary links to make sure the primaries  
fully open up. It is worth the time and effort. You cannot do this by 
yourself.  The cross-shaft movement when man-handled by the mechanic does a poor 
job of  duplicating what finally dribbles out of the linkage when the driver 
floors it.  Have some lead-foot play corner exit simulations with the pedal 
from the drivers  seat. And if you can cobble up together a full set of 
early-65 linkage, it would  be more "tunable".  
 
For any street setup, stay away from the four carbs open-as-one-linkage. It 
 hurts part throttle opening response. Fine for racing where you rarely 
come off  a closed throttle at less than a couple of thousand RPM. A street car 
will fall  flat as the air flow slows and the fuel drops out of suspension. 
Big accelerator  pumps can mask some of this - you will need all four - by 
gas mileage really  suffers and driveability? Well, there isn't much to 
speak of. The 4-as-1  throttle linkage forces you to drive like a madman. (Hmmm 
- on second  thought. . . . )

 
Seth  Emerson

C's the Day! - Corvair, Camaro,  Corvette