What jet size to start with on a 212cc on alky?
- Thread starter W Lindsey
- Start date
Rippin&Tearing Racing
Member
I startrd at .032 on the low side
and .055 on the main and adjusted from there on a stock carb. But I also reamed the bore out to .645 diameter. You can go bigger but you'll end up cutting into the low side passage if not careful.
Last edited:
alvin l nunley
Site Supporter
Alcohol burns best with an air to fuel mixture ratio of about 6.5 to 1. Gasoline burns best at about 14 to 1. So you need about 2.15 times more alky than gas. Depending on the jets you have now, you need to replace them with jets that are 2.15 times bigger, in area, not diameter.
For instance; if you are now running a .039” jet, with gas, you will need a .057” – .058” jet, (113% more area with the .057”) if you switch to alky. Same thing with the low-speed except different size Jets. If your low-speed jet is .018”, replace it with a .026” jet. (109% more area) Calculate the area of the jet with the formula Pi x radius squared.
This will get you very close, but go slow. Better too rich than too lean to start.
If you drill the jets, be careful, there’s no telling exactly how much a drilled jet will flow. If it was me, I would flow test the jets just to make sure.
I know I know, nobody else goes to this much trouble, but it’s worth it.
comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.
For instance; if you are now running a .039” jet, with gas, you will need a .057” – .058” jet, (113% more area with the .057”) if you switch to alky. Same thing with the low-speed except different size Jets. If your low-speed jet is .018”, replace it with a .026” jet. (109% more area) Calculate the area of the jet with the formula Pi x radius squared.
This will get you very close, but go slow. Better too rich than too lean to start.
If you drill the jets, be careful, there’s no telling exactly how much a drilled jet will flow. If it was me, I would flow test the jets just to make sure.
I know I know, nobody else goes to this much trouble, but it’s worth it.
comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.