<VV> Fuel Mileage with a Tweaked Carb

Mikeamauro at aol.com Mikeamauro at aol.com
Tue May 27 20:47:58 EDT 2008


 
"...Craig replies:
You da man, Mike! I've wanted to do this for years but  never got around to
it. The stock carbs are jetted rich - I've often wondered  about folks who
put in #53 jets "for more power" since the stock calibration  is already at
the "max-power" AFR.  FWIW, 14-15 AFR isn't "Lean" except  in relation to
stock.  15.5 (or even 16.5) is considered the AFR for  "Max economy" and
beyond that is considered "lean". EGT (and NOx) goes  ballistic somewhwere
above 14:1 so above that point it pays to monitor EGT  with a pyrometer.
1250-deg F. is considered the max for a diesel engine. Does  anyone know what
the limit is for a gas engine?  Are you doing these  adjustments on the
"high-swirl" engine you built a few years ago?  If  so, it should tolerate
15.5 or more AFR. What size jet are you down to,  48?  Are you using a 65-6
power-valve carburetor so max power isn't  compromised?

Great work - you're a pioneer now!
Regards,  Craig..."

 

"..Are you doing these adjustments on the "high-swirl" engine you built a  
few years ago?..." 
Yes, the 110 engine with heads reworked to a .032 quench distance,  
maintaining 9.5:1 stock compression ratio.
 
"...What size jet are you down to, 48?..." No, not yet... gonna' try that  
next. So far I've re-jetted back down to 50s (which are the stock jets). I did  
have 53s installed.
 
"...Are you using a 65-6 power-valve carburetor so max power isn't  
compromised?..." Yes, but I've weighted the power valves, some, by filling  in the 
hollow tops 1/2 way with soft solder. As I reduce jet size further, I may  need to 
revert to stock, non-weighted power valves. 
 
My ultimate goal is to center AF ratio around stoichiometric (14.7) as much  
as is possible with carburetors. If I can get a bit leaner under light 
throttle  conditions, that would be a plus.
 
Thanks for your comments, Craig.
 
Mike Mauro








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