[gtofreek]

I have built over 100 Q-jets over the years, but all mainly just stock rebuilds. Never tried modifying anything. So I know how they work for the most part and all but my questions are:

1. What is the big, round plastic cup that sits in the front corner of the float bowl on later carbs? Carb in question is a # 17058204. I see no purpose for it and it seems to me if I remove it, I will have a little more fuel in the bowl, and no side effects. Is this correct in thinking? Why is it there anyway besides to block off the hole that I have seen an electronic gadget sitting in in later years?

2. On the adjustable piece that threads in to control how far the main metering rods sit in the jets, is there a best adjustment for it? I always have just put it back where it was and have had no problems with it, but just wondering. Or do you make the final adjustment on the car with it running? This one was 6 3/4 turns up from bottom or 2 turns down from top.

Thanks!

[67cruiser]

I always used 4 turns fron the botton for starters. you must use that round plastic cup, its like a filler cup to simplify it a bit. Yes you can make additional adj. after car is running.but that has always been a good starting point for me.

[gtofreek]

What do you mean by a filler cup? What happens without it? Just trying to understand it's purpose.

[Kenth]

The plastic cup was used to prevent fuel slosh at inspired driving, it was not used in many later applications and can be left out with no ill effects.

I have seen the APT adjustment screw sit from 2.25 to 3.75 turns up from seated in different applications.
As 67cruiser says, 4 turns up is a good starting point.

Leave the aluminium plug out and adjust the APT if needed.
Set fast idle cam at 2200 rpm, warm engine, close chokeblade slowly or with the palm of your hand and notice the first change in rpm.
If rpm´s decrease the mixture is too rich and the APT screw needs to be lowered some, if the rpm´s increase more than 150 rpm´s the mixture is too lean and the APT screw needs to risen, what you´d like to see is a rpm increase of 25-50 rpm´s indicating a slightly lean condition wich is prefered and near optimum.
Jetting may have to be altered to achieve desired result.

Hope this helps some....

[gtofreek]

Thanks guys, I thought 6 3/4 turns up seemed a little high.

[Jeff Walker]

One note on the APT adjustment method Kenth recommended. This method cannot be used on carbs that have Primary Pullover Enrichment. These carbs are identified by the two extra tubes in the air horn. When you start closing the choke on that style of carb you will activate that circuit, throwing off the the RPM change in relation to your APT adjustment. HTH

["QUICK-SILVER"]

Originally Posted by gtofreek

Thanks guys, I thought 6 3/4 turns up seemed a little high.

FWIW Last one I pulled apart for a stock rebuild and found the APT set that high, figured it had to be for a reason. Upon further inspection, found a tip on a down tube folded flat.

[Kenth]

Hi Jeff, i have yet seen a "M" Q-jet with POE?

[Jeff Walker]

Originally Posted by Kenth

Hi Jeff, i have yet seen a "M" Q-jet with POE?

While most of them aren't there are a few that are. I just did one a bit ago that had it. it was originally from a 76 Caddy..

[Kenth]

Ok, thanks, learn something every day!
Ain´t to many of those Caddy´s over here....