I would like to be able to access my power piston and adjust it easily. Once I push this plug back into place, it's not coming out again without taking off the top of the carb. So what other idears you all tried that will allow me to plug and unplug this hole, yet will allow me to mount my air cleaner to the carb properly?

Thanks

 

This is a q-jet, right?

I've seen outfits that drill a hole in the airhorn and put a Holley-type bowl sight plug in it.

 

yeah, sorry. Q-jet.

I don't see how this holley sight plug is possible. First I see no use in visualy looking at the power piston. Second the sight plug will interfere with the air breather seating properly against the carb. If I'm missing something, please elaborate.

Either way, thanks for the idear though.

 

It's been a long time. I forget how they did it - filed it down across the air cleaner gasket or something.

Maybe someone with a better memory can chime in.

 

drill a hole in the plug, but do not go all the way through it, then thread the hole. when you need or want to pull the plug, get a screw that fits the threads you put in the plug & lift it out.

 

First off, only SOME QJets even have the APT (Adjustable Part Throttle) adjustment you need to even do this. It's sits in a little well just in front of the power piston itself and has a slotted head that can be turned (with the right tool) to limit the downward movement of the primary rods in their jets. i.e. it can allow slight adjustements to the cruise/part throttle A/F ratio. Does nothing at idle or WOT.

The power piston itself has a little metal dowel that sticks over through a slot into this adjustment well. The dowel comes to rest on a flat "shelf" built into the head of the APT screw. Moveing the adjustment screw moves the "shelf" up or down and therefore adjusts the height of the power piston and therefore the height of the rods in their jets. Since the primary metering rods are tapered allowing them to go further down leans the mixture, raising them richens the mixture.

I drill the casting out above this adjustement well from the INSIDE of the airhorn casting (to make sure it's properly centered over the well- there is a matching "silo" on the inside of the airhorn casting abore the airhorn casting) and then tap the opening with threads to take a small pipe plug with an allen wrench fitting on top. That way I can just unscrew the pipe plug to access the adjustement screw inside the carb. I usually end up grinding the plug flat on top to match the height of the top of the carb around it.

I don't recall the plug impinging on the air filter gasket area very much but it's been a while since I did one of these mods.

FYI- the adjustment screw has about 4 turns of "adjustment range" in it. The first 1/2-3/4 of a turn up (CCW) from fully seated is basically "slop" and doesn't raise the power piston at all. Then you get about 4 turns of adjustment range above that, then you're basically on the power tip of the rods, if the adjustment screw doesn't just unscrew from it's threads and fall out completely.

 

If you notice my picture above, the silverish circle is the plug in question. Follow the lines of the air breather and you see that it goes right over this area.

Beneath this plug is an adjustment screw that you specify. While rebuilding the quadra-jet I took my dremmil tool and cut a slash in the top if the screw so as to be able to use a screw driver to adjust it.

See my webpage below for a link to my quadramods.

http://www.angelfire.com/clone2/tony/MyZ.html

 

I was under the impression that you set this to have your primary rods in the "right" spot, such that when the power piston spring raises your rods, they go to the power tip, and under vacuum, they're at the fatter spot (the width that the rod is spec'ed at, like .043").

I thought you set this 'right', not really as an adjustable part. Is the idea then to have your power piston pull up sooner? like using a stronger power piston spring?

 

Would you quite being so observant. When I rebuilt this carb, I didin't take note of how many turns in/out the screw was. And I can't get a definate answer as to where "right" is. Some say 2&1/2 others 3 and others 3&1/2 turns out.

When I install the carb I don't wanna have to remove the top of the carb to adjust this screw to find the "right" spot.

 

ooohhhh... why didn't you just say so?

right click, save as.
https://webdisk.ucalgary.ca/~jmknopp...owerPiston.doc

use a calipers depth gauge (or your little rebuild kit measuring 'L').

 

Actually, adusting that is often used to tune out the off-idle flat spot you get when using an open element filter rather than a thermovac-equiped snorkel air cleaner.

 

I think I figured it out, Hows this...

Scroll down and read under screw mods. Collection of Quadra Mods

 

these 2 pictures didn't work for me...?
http://www.angelfire.com/clone2/tony...istonPlug2.JPG
http://www.angelfire.com/clone2/tony...istonPlug1.JPG

 

The adjustment is just that- an adjustment. On a stock engine with the correct carb maybe you can adjust it to a certain number of turns and be reasonably close. On a modified motor with a mish-mash of parts on it...... who knows.

Try it and see. But I'll tell you this..... most stock/emissions QJets want to be a fair bit richer than stock when put on a performance engine. 2 jet sizes bigger than stock with the same rods is a safe bet on most street performance applications. For instance, I often run a #76 primary jet and #74K primary rods (APT screwed all the way down, essentially disabling it) as a starting point for most Qjets of that vintage intended for a performance application. I bet you currently have something like #72 primary jets and #44K primary rods and the APT screwed out about 3 turns. In all cases my combo will be slightly richer than stock.

A "K" style primary rods only has about .004" difference in it's taper until you drop off the ledge and go onto the power tip. For instance, a #44K primary rod starts out at .044" at it fattest part, and skinnies down to .040" along the taper and then it drops quickly off a step onto the "power tip" which is .026." The tapered part is the part along which you are adjusting when using the APT screw. As you can see, it's not like it's got a huge adjustment range.

 

There, I modified the webpage. Pics work now.

 

damon, you meant 74 jet, and 44k rod right?
when you set the APT all the way clockwise, wouldn't it be full lean, and NOT as rich as 3 turns out??
what am I missing here?