carb problem?

[runawy9]

850 mighty demon carb with annular boosters.
Chevy 365 c.i.
Dart 230 platinum heads
10.7 to 1 compression
.585, .600 lift 243, 249 @ .050 solid roller
Victor Jr. intake
MSD ignition set at 18 initial with 38 total
The problem we are having is at idle it will smoke you out of the garage and make your eyes burn.
It will idle fine and has great throttle response.
I know that Demon carbs are problematic at idle and I know the heads are waaay too big also.
But it should be able to idle without gagging innocent bystanders.
Any help or guidance would be appreciated.
I'll try to answer any questions you may have.

[Schurkey]

Eye-burning, hard-to-breathe fumes from the tailpipe are high HC emissions, often the sign of misfire. If you have an exhaust gas analyzer, you might find high O2 readings also, which would confirm the misfire.

A cylinder-balance test might locate a dead cylinder at idle, but the misfire could be random.

[pamotorman]

try leaning down the IFR with a piece of .015 diameter wire and see what happens

[jmarkaudio]

With a cam that large you need more initial timing, as long as converter stall is above 4500 I would lock the timing to full advance. With a large cam idle vacuum is low, so throttle blade can be over exposed as well. After you work on the timing make sure you have no more than little squares showing of your t-slots if you pull the carb and turn it over. If it does you will need some idle bypass air, again this must be done after timing is maximized. If you have insufficient converter stall, too low numerical gear ratio rear, or a stick with a low number rear gear you may need a vacuum advance to get the idle timing up but pull it out under a load.

[kirkwoodken]

With a cam that large you need more initial timing, as long as converter stall is above 4500 I would lock the timing to full advance. With a large cam idle vacuum is low, so throttle blade can be over exposed as well. After you work on the timing make sure you have no more than little squares showing of your t-slots if you pull the carb and turn it over. If it does you will need some idle bypass air, again this must be done after timing is maximized. If you have insufficient converter stall, too low numerical gear ratio rear, or a stick with a low number rear gear you may need a vacuum advance to get the idle timing up but pull it out under a load.

This should be a sticky!!!!! Fix timing first. Square transfer slots. Admit idle air by adjusting secondaries slightly open or by progressively drilling larger holes in throttle plates until idle speed is correct. These simple procedures can make huge difference in driveability.

[F-BIRD'88]

auto trans: Lock out diz mech adv curve. Reset pri and sec throttle T slot exposure.

reset idle mix screws. enjoy.

[runawy9]

Car is 4 speed manual with 4:11 gears.
Transfer slots on primary and secondary are approximately .040-.050 exposed.
Idle is right at 1100 rpm.
Have already tried adjusting ifr, fuel pressure, float levels and idle screw and power valve.
I don't think the car will start if I give it any more initial timing.
The owner is on vacation till the end of this week. When he returns I will try more timing.

[F-BIRD'88]

4speed 26 initial 10 deg curve 36 total.. 10 - 12 deg of vac adv. ported vac.

hot start cured with simple ignition power interupt switch.

be sure gm starter motor brace is on it.

too much t slot exposure.
at idle. fix that. pri and sec
will idle at 800 rpm when all done.
much cleaner idle. better driving.

limit mech adv to 10 deg.

[F-BIRD'88]

Using the wrong pcv valve (generic for stock motor with stock cam can be a critical issue..
getting the pcv valve right matters..
They are not all the same.

A Heated intake manifold plenum helps too. improved fuel vapourization better a/f mix.

[levisnteeshirt]

try a lower power valve ,, like a 6.5 ,, and see if the current one is busted , or stuck open

[cgarb]

powervalve would be my first check.

[EVL253]

open pv at idle wont change anything. blown pv will.
do all as said above then try smaller idle feed restrictors

[BigBlocksOnTop2]

I'm was working on a 750 BG Mighty with annular discharge this morning. A/F cruising is 12.7-13.1. The IFR are in the bottom and was .040. I have changed that to .031.The low speed bleeds is .077''.This was done on the primary side (I'm still tuning). Now the A/F cruising is 14.3-14.7. VooDoo solid mech. with 249 @ .050 intake. Timing at idle 28° with 9° mech adv. SBF 395 cu. in. I have a surge in it and it surged even at 12.7-13.1 A/F. I suspect the mech. adv. springs are causing this. Got 75 and 82 main jets and that is pig rich at 11.1 A/F (quick glance) at the top of second gear.E- Bleeds are .026, blank, .026, blank, blank. With the change to IFR and low speed bleeds the idle is nice and it wont run you out of the garage.Get the timing up higher too as outlined. Hope some of this info helps.

[runawy9]

Advanced the timing to no avail.
Still eye burning smoke in the garage.
I did find out the gas is from last year and the plugs are ngk -8 which I think are a little cold for this combo.
Anyone have suggestions from here?

[jmarkaudio]

8's are way cold, try FR5's. And still give it timing as muchh as the fuel will tolerate. And fresh fuel.