To add to the cost, install an Air Fuel gauge to the dash and O2s in the exhaust, it will cut tuning time in half. You will still need to know what the gauge is telling you and how to correct the problem, but when asking for help you will have numbers instead of ( it feels likes ). Seat of the pants will get you close, A/F gauge will get you on the money. I have a SpeedHut stand-a-lone gauge in my '37, everyday is a different reading due to air pressure and temperature, fuel station choice also changes the reading. Mine averages 14.7 to 15.5 running around town, mid to upper 15's on the highway. I changed metering rod depth on twin W-1 Carters by .025", the ratio went up .5 to .7 percent leaner . I have special fixtures to hold a dial indicator to set rod depth and throttle opens. Floats are set with dial calipers, I have a modified Unisync synchronizer for setting idle speed.
Just to point out how sensitive the air fuel gauge is, I sanded .005" off the metering rods second step to cure a part throttle lean out, the gauge pickup on the small change.
When we say both carbs need to be identical, you better believe it. Smaller carburetors keep the air velocity high, somewhat close in the range the carb was designed for. Add larger carburetors, the signal will be half what it should be.
I tried dual Monojets on a 250. Both carbs came off 250's from 1970, both set up the same. It ran decent, smelled terrible, ran pretty strong at full throttle, and the really neat part was you could actually see the fuel gauge moving! I switch it over to dual W-1's from the 216 engines.
This fall I install a catalytic converter just for the fun of it. The exhaust is as clean smelling as any new truck. Twin Carters from the '40s on a '70s inline six 250, HEI ignition, factory exhaust, gets 21 mpg @ 65mph running A/C at 2400 rpm, it gets better mileage then my '03 Toyota Tacoma.
Last edited by Joe H; 12/19/2024 5:37 PM.
