adjustable secondary air bleed?

[novadude]

My 17085213 carb has a staked-in plug in the rear where the hot idle compensator would be on an older carb.  From looking at the passages to-and-from this area, it looks like it might be some kind of adjustable secondary air bleed screw that picks up air from the rear of the air-horn and connects it to the secondary wells. What's the deal?  I've never seen this on any other Q-jet? 

[omaha]

Things that make you go "what the heck".  Got a picture? If it goes to the secondary wells, I do not under stand that. Maybe some type of vapor bleed or marine application. I noticed the original application is for chevy truck with 305 or 350 so maybe a bleed might be possible as chevy was trying hard to clean up their emmisions during the later years of the qjets production. I find it hard to believe that an adjustable air bleed would do anything on the secondary side. maybe the bleed worked in conjunction with the compensator.  I don't know I've not seen anything like that yet.

[novadude]

I blatantly stole this picture from somewhere else, as it is too cold to photograph mine in the garage! 

Check out the weirdness between the secondary throttle bores in the main body.  The hole at the rear extends up a small vent tower in the air-horn, and a staked-in plug comes in from the rear and seals off what seems like it could be and adjustment screw (I've not tried pulling the plug).  Looks like this passage goes straight the main wells. 

I'd imagine you could block it off and have the secondaries function like a normal q-jet.  I've just never seen this before and was wondering when, and why it was used.

[omaha]

Wow that is the weirdest Qjet I have ever seen. I guess that 85-86 was the last year for the Qjet. Obviously the discharge tubes coming from the back side of the carb are exactly that.  but does it have the other discharge tubes in the top casting. wonder if you could even get a gasket kit for it.

[Cliff Ruggles]

Those carbs were used on Motor Home applications.  Not a very good system from the testing I've done with them.  I block them off here, and tune them as any other q-jet.  There is some cfm lost due to the design, so for high performance use I typically avoid those castings.....Cliff

[novadude]

Thanks, Cliff.  I actually grabbed this one from a boneyard for parts from a '85 Step Van (think commercial bakery truck), so it's probably the same chassis as a motorhome.  I never saw anything like this before, but it does look like it would be easy to block off this air passage.  I do see what you mean about the casting protrusions in the secondary bores in main body.

Guess I'll keep this one for parts (the original plan).  I needed a base plate to replace a cracked one on an otherwise nice Edelbrock 1903.  Baseplate is the same casting number, and appears to have all the right vacuum passages that I would need.  Idle transfer slots are a bit longer than others I've seen but that's probably not a big deal (per you answer to my earlier question).

[Cliff Ruggles]

I typically avoid the motor home units for any sort of high performance use, at least until I use up everything else around here.....Cliff