primary rod height

[FNG]

have been reading this great forum a couple days now and have learned alot.read a thread in the problem solving section where it was suggested that he check the primary rod height in the jet.i did not find exactly where this should be.so as i'm putting mine together and double checking every thing,with the apt seated the .044 portion of the rod is right about the top of the jet hole.this sound right?17080272 carb with all cliffs goodies

[FNG]

i think cliff covered this in another post,its on the power tips up and at the .044 when down.i think i;m good on that,but i did stumble on cliffs ventura on another web site,glad to see hes a pontiac guy,and maybe give me some ignition timimg pointers,etc from his vast experiences,thanks

[von]

I once cut a jet in half to see it in cross-section and placed a primary rod in it to see the relationship at various rod heights. In order to have the rod at the proper positions at high vacuum (idle) and no vacuum (WOT) and using the typical piston movement measuremant, it looked like the best position at no vacuum (piston depressed against the spring) was to have the step from the taper to the main rod diameter right at the top surface of the jet. I put the rods at that position by bending the hanger as required (usually puts them back to about their original shape). To make it easier I mark the edge of that step on the rod with a Sharpie and use a tiny flashlight and magnifying glass to view the mark's relationship with the jet with the piston depressed. I've done several Q jets like that with good success.

[Cliff Ruggles]

The 17080272 carburetor uses APT, so you have full control of the tapered portion of the metering rods in the jets.  Most of those came with "K" metering rods, which only have a .005" tapered upper section, and are stepped.

If you switch to full tapered rods, there will be more control with the APT system.

Metering rod to jet height relationship is critical, but not really that "fussy".  The later carbs using the APT system provide the tuner will fun control of the part throttle A/F using the right parts.

The builder/tuner just has to make sure that the rods are fully up on the tips in the lower lower portion of the jets when the PP is all the way up.  You have control of their relationship when the PP is down via the APT system.....Cliff

[von]

I should've added that it was for non APT carbs. On those, as Cliff says in the book, many hangers end up bent from improper prying technique during removal. Some of those bent ones put the rods too far up in the jets at high vacuum position.