Q jet primary jetting?

[Lyn Smith]

When you remove the primary metering rods on a Q jet,how many sizes down do you normally go on the jets?

[Dean Oliver]

Lyn,

The math tells you to go between .004 and .005 smaller. I go .004 smaller, so if you were running .072 jets with rods you would run .068 jets without. (That assumes you have .026 tip primary metering rods.)

Dean

[Alan Roehrich]

The question is, SHOULD you remove the metering rods?

[Dean Oliver]

Alan,

There is no performance advantage to removing the rods, unless the power system has not been properly set up for a racing application. Removing the primary rods basically just makes the Q-jet easier for the average tuner to disassemble and, particularly, re-assemble. On my car and many others, we have seen no improvement in ET anywhere down the track when converting to the "no rod" set up in the primary. But ask most racers what they don't like dealing with the most on Q-jets and usually they will tell you the power piston installation. Some racers never change their primary jetting because of it.

Dean

[Mike Pearson]

Dean,

What do you do with the hole where the plunger used to be? Or do you just leave the plunger and remove the rods?

[Dean Oliver]

Mike,

The piston can be left in the carb with the rods removed, but that still leaves you with the potential to tear the top gasket when working on the carb. I would recommend either plugging the piston bore with a "freeze plug" type plug or with a shallow 3/8" setscrew. That way you don't have to worry about damaging the top gasket when you are removing or installing it around the power piston which no longer serves any function with the rods removed.

Dean