Is this the long little slot in the housing that the butterfly covers? If so what do you use to measure it ? could someone please explane this to me everything i read talks about it, but no pictures.

 

if you got the carb off the motor(or take it off) turnyour idle adjust screw until the slot makes a perfect little sqaure..put back on motor and you might then have to adjust mixture screws..if you have mech secondarys,you have set both slots the same

 

IT is the slot in the base of the carb, if its a holley than it should be around .025 wide and around .200 long on average. I use a set of feeler gauges and a slide caliper to measure the transition slot. I'll try and find a pic for you.

Neal

 

The terminology I heard esplained to me some years ago was Off Idle Transferr Circuit....what happens is the idle is set correctly, but when the throttle is opened, there is an immediate need for more gas than available throug the primary jets, because the throttle is opened so little, .....the engine leans out and stumbles, maybe dies....later Qjet engine had EGR, putting some inert exhaust gasses into the induction, thereby lessing the need for fuel....to go with the fresh air....it seemed to be a 4 cyl engine....the reason a '70's car seemed so anemic untill satisfactorily desmogged.....

which involved....richening up the off idel transferr circuit....

and in a Qjet, there are two capillary tubes (out of 4) pressed in the top plate....the smaller two, need drilled to pass more gass outta the bowls up and over top and into the off idle slots....vacuum operated like everything else in a carb.....

that is roughly the way it was esplained to me some years ago..and it makes total sense.....

no amount of normal rebuilding can make the carb right, it has to be modded....

assuming it's right, and was a stock carb at one point in it's life....

 

I read about the square but didn"t understand. That"s the best explanation i"v read in 2 days and i read a bunch!

 

I still dont understand this part, unless your useing some type wire feeler guage. No reg feeler guage is going to go in a slot that small. maby there just holding a feeler guage up to the hole till it"s completly covered, doesent seem like a accurate reading cerently not accurate enough to check the feeler guage with a slide calaper.
It"s a holley 750 mech secondarys and like a idot first thing i did was idle it up with the curb screw!!! I had 5 hg so i changed out to a 2.5 power valve. ok now i can adjust the idle screws max vac and rpm is at 3/4 turns (on all 4 screws) car feels week came out to 1 turn still week at 1 1/4 it starts to feel better, it feels best at 1 1/2 turns but i been around top fuel cars that didnt burn my eyes this bad! Could the idle transitation slot or (off idle transfer circuit) be causeing this?

 

No. It's the idle mixture of air and fuel having more fuel in it than it's supposed to. You need to lean out the idle mixture by decreasing the size of the idle feed restriction in the metering block(s).

Brett

 

ok , I admit it worked a lot better than it sounded, i set it to .020 with a reg feeler guage and it looked square. Put it on no differance, except it wouldn't idle. (oh by the way this 750 doesen"t have a transtition slot that even reaches the butterfly on the secondarys!) Well took it off, held it up to the light, set the rear so it had same size crack as the front. Now i have 4 idle adjustment screws that work!!!!! and it idles at 800 rpm. holley tec said return to the most vacume setting on idle mixture screws and start going up with the front jet sizes the power should come back watch the plugs.

 

My Holley and BG setup papers cover this process in detail. E-mail me if you want copies:
V8FastCars@msn.com
Lars

 

Thanks for the offer Lars i found your info here http://www.lbfun.com/Corvette/Tech/vettetech.html

I try to read and learn as much as possable on my own, but sometimes this stuff doesent make sence to me. For example: I"m rich on idle, bad fumes, so holley says go larger on the primary jets?

 

Even though you have a Holley, be sure to read my BG setup paper as well - it has a lot of good info for Holley setup.

If you have primary and secondary throttles cracked open equal amounts at idle, the idle mixture screws should be effective at all 4 corners. If the screws respond, there should be no limitation to being able to lean the idle out.

 

I would like to hear a little more about this idle feed restriction. The holley book is not a lot of help with this (no picture) it does speak of useing a .010-.015 piece of wire to lean the mixture or replace with a smaller drilled size. I"m not to fond of useing the wire trick but i would like to try replaceing with a smaller size, if i can figure out exactly what your talking about.

 

ok, i found a pic i see exactly where they are.

 

Just so you know, a regular office staple out of a stapler is .015 to .016" diameter. Since they're pre-bent, they make perfect IFR restrictors...

 

Well i got tired of pulling hot plugs on the side of the road with one black glove pretty quick. Started to feel like oj. Off to the dyno i went, now my jets are right. Ended up with larger jets in the front and smaller ones in the rear. Guy said don"t see that very often but he has seen it before. He also said whats going on is what you call a lean missfire condition. i pulled the plugs they look fine , let it idle for about 10 mins and looked again still look fine maby a little darker than the highway run but not bad. i installed a new set of plugs, i"ll keep a eye on them for a few days before i try the staple trick. The idle mixture screws are still at 1 1/2 turns, they were going to adjust them, soon as they closed them a little it wouldnt even take off in 1st gear on the dyno, you should have seen the look on there face"s right about then I know new plugs dont change color as quick as old plugs, but if they stay tan at idle in a couple of days driving am i ok at 1 1/2 turns or do i still have a problem?