<VV> 140 carb jet sizes

NicolCS at aol.com NicolCS at aol.com
Sat Oct 15 16:49:43 EDT 2005

Jim asked:
Hi All,   I have a 1966 140 4-speed convert, no smog heads, no A/C. My info  
suggests main jet size is 0.050 and secondary carb jet size is 0.046. I am 
completely satisfied with the performance (not smooth at acceleration  2000 
RPM to  3000 RPM and  some hesitation/lurching as secondaries kick in.  I want 
to know if anyone else is using jet sizes different from factory  recommended 
sizes to get smooth acceleration and secondary transition.

Craig Responds:
Before I changed jets, I'd look at the timing of the secondaries and I'd look 
at the ignition system.  Yes, it sounds like lean misfire but dumping the 
secondaries in too soon and ignition breakdown will create those reactions too.  

If the secondaries dump too soon, there isn't enough airflow throught them to 
pull in an adequate amout of fuel leading to coughing and lean misfire.  If 
your plugs or wires breakdown (electrically) at higher pressures, you can get 
misfire that way as well. Are you running a conventional plug (larger spark 
kernel than platinums and more tolerant of lean mixtures)?  Gotta good coil 
output?  Good silicone wires?  My 140/4 is running the same 50/46 combo and runs 
extremely well, but we don't "get" to have oxygenated fuels here.  You might 
need to bump the jets slightly if that's what you have in your area.  I run a 
pertronix, MSD-5, silicone wires, and Bosch 7502 "supers" (a conventional plug)

Oh, one other thing, the 50/46 combo works best with powervalve carbs.
Craig Nicol
1 Carbureted 140
2 EFI 140s

More information about the VirtualVairs mailing list