so i tore my barry grant carb apart...
 

in the hopes of changing the base plate for something that had provisions for a pcv or vacuum advance.

i have a smallish holley vacuum sec that works well but wanting something larger i could hook up a pcv to and vacuum advance. i knew bg had in the later years changed to a system where the idle could be adjusted with a screw in the middle of the carb allowing more air into the mixture so the butterflies could remain in a more desirable position. and this is what i found.....

the base plate has the provisions, but the main body does not:LOL:. you can see from the pic the base has a brass fitting that would fit into the center, this fitting goes in from the top, and then the best i can figure is there is a screw that runs through the body and either seats on the brass fitting or allows air into the stream, via the small slits you can see just below the gasket in the pic. so this carb didn't have the screw so was allowing air into the intake without any fuel, the orifice is probably 3/16" diameter in the brass piece, maybe 1/4".

i guess i got the changeover parts or clearing house deal. i have heard bg is trying to make a comeback, maybe i will address this with him then.:3DSMILE:. i still like the quality of the carb pieces, just there qc somewhere went to sheit imo.

i tried to make it adjustable, so i drilled so carefully centered and straight with the drill press and it was still off centered at the brass seat by half of the 1/4" threaded rod, so i plugged her. the brass seat was metric btw%/, but i fixed that.:3DSMILE:

I wrestled with my BG's for years and never could get them zero'd in. I finally took my car to Barry R in Detroit last December and he put a couple Quik Fuels on top of my engine. The BG's are on a shelf somewhere, and I have never looked back. :) Good luck with yours, I hope everything works out.
steve

So you had a manifold vacuum leak with an I/D of 1/4 inch?

Would have been a pain to get a respectable idle.

You can convert your current base plate by adding the "idle-eze" adjustment screw, and drilling through the base of the aircleaner stud hole to make it all work.

do you have a pic of the setup or a link? i drilled through the body but am unfamiliar with how the adjustment screw setup looks.

Here's a link:

Recent News from Barry Grant

thanks for the link. i see now how they do it, using the spring to keep the screw from moving, how does the screw look though, i wonder if it has a notch up the side to vary the air flow.

on second thought, i bet it is the spring that regulates the air flow. compressed no air flow, expanded flows more air.

No, the four milled slots in the top of your throttle body feed filtered air to the central bore below the aircleaner stud.

The "valve" has four holes on it's perimeter, which allows the air to enter the centre which has a blunt tapered screw residing near it's seat.
It's a simply an adjustable bypass to allow idle speed adjustment without touching the base idle setting of the throttle butterflies.

Best idea for 4 barrel carbs yet.

Pity QFT doesn't offer it.

Weber has used this on several of their carbs, most notably the 40 IDA-3 (3 BBL) used on the 6 cyl 911 Porsche. With all things being equal, it allows a variable air bleed to be opened to even out the amount of air being draw in into each cylinder. I wish the 2bbl 48 IDA had this feature.

i see. i was thinking something like a screw used for the squirters on the carb, and the brass fitting looks very similar to a fuel jet. since bg is tits up i might have to try and rig something up, plugged right now.

You just need to cut a relief in the top of the baseplate so some air can get from the throttle bore to the center hole--then use a holley alcohol jet( or drill the one you have until you get the idle speed you want) I find that most times it takes around a .105-.110 hole to idle at 850

So he already has the milled slots above the plates, reducing his centre bleed from 3/16 or so down to .105 should fix this.

I've modified/blueprinted hundreds of holley type carbs for some big cam engines and generally around .105- .110 will get the idle to around 850 with the butterflies adjusted to where the transfer slots are the little perfect squars---Sometimes I take a .025 drill and reverse broack a little exact hole there with the plates just lightly snugged closed---will need about 1 1/4 turns on idle air screws

thanks for the info, i was thinking it would be easy to do to some other carbs as you described.

""Sometimes I take a .025 drill and reverse broack a little exact hole there with the plates just lightly snugged closed""

Jerry, could you describe this, i don't follow.

with the throttle plates completely closed, I take a .025 drill bit in a pin vise(a hand held tool for twisting a very small drill)thread it into the slot, hold the t plate against it and then pull the drill bit straight out of the slot, which will reverse broach the hole to a perfect .025.(I don't twist the drill as that will sometimes break the bit) When done, I have 4 perfect .025 openings at the t plate/transfer slot---this will then be round holes insted of the squares of the t slot/t plate----then the idle speed is set by the .10x hole in the center hole between all 4 t plates-------

Jerry, that sounds intriguing, would you have any pictures of that mod? I’m having a hard time wrapping my little brain around it.

I don't think I have any pics of it on my present computer, I do think that I posted some 2 or 3 years ago on here on somebodies thread sorta like this one but don't remember who's or when or subject title---

I'm getting ready to go to Colorade for a buddies 50 anniversity and we're going up Pike's Peak on Sunday so I will take some pics and post it here next week

Basicly, It creates a path for air that has been thru the filter a way into the manifold, and the center of the base plate puts it into the best place--If you look at the base plate in the pic in this thread, it has a gasket on it blocking the view of the slots(an X that is milled connecting the four throttle blade bores) but you can just make out the end of the slot in the bore facing the camera. That jet that is there then restricts/regulates the amount of air that can pass into the manifold without going thru the throlle blade bores.This method of regulating the idle air flow there then lets the idle circuits and transfer slots to work to perfection---(remember the older holley big engine carbs had holes in the throttle blades?) well, they were too big and let too much air thru for the carb to idle, so then you had to open the blades for idle so it idled at high rpm, which then advanced the timing which then dieseled when you tryed to shut it down????????????????

This system will allow the engine to idle at 850 or so and below the rpm where the ignition advances and the proper function of the transfer circuit will let it REV off idle like the modern FI cars