Six Pack: Why do they have secondary idle mixture adj?

Posted By: ragtop

Six Pack: Why do they have secondary idle mixture adj? - 09/02/13 10:45 PM

Why do Six Packs have idle mixture screws on the outboard carbs? Are they necessary? Theoretcally, what would happen if you turned all of the outboard carb screws, in all the way? Thanks.

Posted By: ScottSmith_Harms

Re: Six Pack: Why do they have secondary idle mixture adj? - 09/02/13 10:55 PM

Quote:

Theoretcally, what would happen if you turned all of the outboard carb screws, in all the way? Thanks.

They supply fuel to the forward and rear cylinders while at idle. If you shut them off a dangerous lean condition will likely occur, this can cause burned pistons, etc. That's why the factory adjusted them and staked them, to help keep owners from burning up their engines practicing their tuning skills.

Posted By: macmic87

Re: Six Pack: Why do they have secondary idle mixture adj? - 09/02/13 11:10 PM

the way I heard it is so the fuel is being used that is in the float bowls so at least there is fresh fuel coming in. not that there would be a problem with just jamming your foot down to use the outboards.

also helps with the lean mixture that will happen when the outboards open because they don't have a pump shot.

Posted By: lewtot184

Re: Six Pack: Why do they have secondary idle mixture adj? - 09/03/13 02:30 AM

the chrysler carbs had them for emission concerns. chrysler built their emissions into the carbs and ignition. the corvette holley tri-power doesn't have them; they used an air pump for emissions..

Posted By: 383man

Re: Six Pack: Why do they have secondary idle mixture adj? - 09/03/13 02:59 AM

Most 4 brll carbs and other extra carbs like 6pk's have idle circuits in the non primary brll's. Many 4 brll's have non adjustable idle circuits in the secondary's. Ron

Posted By: jbc426

Re: Six Pack: Why do they have secondary idle mixture adj? - 09/08/13 05:13 AM

I'm running the old Direct Connection mechanical secondary, side hung float bowl carbs. The outboards on this set-up have no fuel/air circuits. It idles of the center carb only.

The factory outboards have fuel/air idle circuits on the end carbs to keep the fuel from stagnating if they are not opened for extended periods.

Due to the weight of my right foot, I don't seem to have that problem.