I was going to send these questions directly to Lars, but I wanted everyone to (possibly) benefit from the answer -- the guy's a GREAT help!!!

Here goes:

(1) How does the nylon collar/retainer on the power piston relate to the vacuum action on the piston? I ask this because two of the three pistons I have don't "lock in"...the nylon collar doesn't retain them against the pressure of the spring. Does this condition result in poor vacuum action on the piston?? Can the collar be replaced? I haven't tried to pull the piston apart (e.g., pull the hanger out of the piston) since I don't know if this will damage it or not.

(2) I have three pistons, as I said, from one "good" carb and two "organ donors" One piston has a "full-length" pin coming out the bottom, one has had the pin clipped at about 1/8" past the bottom, and one has no pin whatsoever. After reading everything I could find from Lars on the subject, I know his advice is to use the one with the full pin. My question is, are there different pin-lengths for different carbs? How can I tell if the pin on this power piston is the correct length for my 7042202 carb or not? Can one find/buy pistons easily? (I haven't found any offered anywhere yet).

The info Lars has published on this topic has been invaluable! THANKS!!

Carb parts
http://www.carbs.net/

Carb info links http://www.buickpartsdirectory.com/carbs.htm

I am no expert but I've spent a great deal of time reading and playing with my Qjet just as you have. It is like black magic and that is why I am finding it so fascinating. Qjets are known for being difficult to tune. That is why a lot of people toss them in favor of a simpler (lesser) carb.

It seems to me that you absolutley must have that nylon collar hold the piston securely in place. If the nylon collar doesn't hold the power piston in place then the primary rods could come all the way out of the jets. They could get stuck out resulting in a super rich mixture.

If you pull apart one of your donor pistons I would be interested to know just how 'serviceable' it is.

This pin you are talking about does it stick out of the side of the piston? If so you are talking about the pin that limits the travel of the piston downwards.