[formulabird428]

A few question about the holley carb:

Hypothetically...If I were to adjust the throttle blades / idle screw so that 0% of the transfer slot was exposed (i.e...how the secondaries are setup)...what would deliver fuel to the engine?

If I restricted whatever supplied fuel for the closed T-slot condition, would this restriction affect cruise...or only the the non-exposed T slot?

Do the main jets affect idle at all?

[Tom Vaught]

Originally Posted by formulabird428

A few question about the holley carb:

Hypothetically...If I were to adjust the throttle blades / idle screw so that 0% of the transfer slot was exposed (i.e...how the secondaries are setup)...what would deliver fuel to the engine?"

The idle mixture channels. The idle mixture channel is a parallel circuit off the "transfer slot /idle port feed passage"

By closing all of the transfer slot you would get a off idle hesitation from lack of fuel in that part of the throttle blade movement.

Originally Posted by formulabird428

"If I restricted whatever supplied fuel for the closed T-slot condition, would this restriction affect cruise...or only the the non-exposed T slot?

The idle circuit & the transfer circuit are both fed by the idle feed restriction. Changing the idle feed restriction will affect cruise jetting to some extent as the idle circuit & the transfer circuit are never totally turned off unless you plug them.

Originally Posted by formulabird428

"Do the main jets affect idle at all?

Main Jetting is typically much larger than idle feed restrictions therefore the main jet has very minimal effect with a very small carb (cfm) seeing more effect due to smaller jetting vs IFR size vs a large cfm carb with the same basic IFR. Normal engines consume from 15-21 cfm at idle and the IFRs range from .028 to .038" in size. Very small changes in the blade position and IFRs can have a big effect where as main jetting can typically be with-in 2 jet sizes and run just fine.

Tom Vaught

[formulabird428]

great answers. right now I have the throttle blades set at about .030 exposed T-slot. the backs are just showing the T-slot (1/2 turn from seated as recommended).

i'm still slightly lean at cruise. and i wanted to make sure that the main jets (78/86 but going to 82/86) would not affect the idle mixture...because I'm already a tiny bit rich there. idle mix screws are 1-1/2 out. carb is 4150.

["QUICK-SILVER"]

What size/which 4150 are you running? And have you got power valve/valves matched to engine vacuum? Dual stage power valves can help a lot sometimes when you're having difficult or unusual tuning problems.

[stickboy]

I have a BG Race Demon. It was setup with a short slot, It would barely stand to blip the throttle, and would fall out if I tried to load it at all off idle. Couldn't figure it out....was ready to start cussing BG.

Disassembled and compared slots to a holley 850 baseplate....it was significantly shorter and NONE was exposed at my throttle plate idle setting. Must have been setup by BG for a race car where they expected a larger throttle opening to keep the car idling.

Careful work with a hacksaw blade and it is now good.

[Tom Vaught]

Good Job, Stickboy. Make a carb man out of you yet!

Tom Vaught

[stickboy]

Tom, I am certainly trying my best....formula428...you have to define "cruise" to know what circuit to try and enrichen. If you are 2200 and up, then yes you are probably on the main circuit. If you are talking super light throttle, then it is probably in the TSlot/IFR circuit.

Low rpm loads w/ OD trans are more tricky to get all tuned in. It is feeding off the TS down there. Sometimes I drive around 16-1800 just barely touching the throttle, but definitely loading the engine.

Are you using AF meter of some sort?

[formulabird428]

I'm going to buy one.

It's pretty light throttle, about 2000. Literally, the engine is smooth as glass from idle to 1900. Once you hit about 2000, it's "misfiring" and the temp will start to climb.

It seems that any RPM between 2000 and ~2800 has a misfire under light accel and in most cases, will start to heat up the engine. If I mash the throttle, it's fine. Any RPM below is fine. The interesting part is...idle (driveway idle...1100rpms) is so rich, the temp will jump down to 160 and even 155 (closing the T-stat) if I leave the fans on for long enough.

[Tom Vaught]

If you can get a couple of pieces of "Tag Wire" (about .017" in thickness) or strip a couple of inches of wire insulation off an old lamp cord, you can make some wires to stick into the idle feed restrictions.

You never did answer what holley you had (the list number) and previous mods by someone, the jetting, the idle mixture settings, the power valves, etc. Hard to help you without better info.

Tom Vaught

[formulabird428]

carb:
* Primary T-slot .030-.040"
* Secondary blades 1/2 turn from seated (about .010" T-slot open)
* 830 HP main body w/downleg boosters, IAB reduced from .073" to .067"
* 830HP metering blocks (IFR reduced from .040" to .036"). I also do have a set of stock 4781-3 blocks that I play around with...seems to help a little, but not much.
* Quickfuel 1-3/4 blade 850cfm base plate (recently bought, neither a help or a hurt). I have drilled the bypass holes in blades to 0.172" to keep car idling and maintain T-slot position. The stock Holley base plate holes were .150".
* 82 / 86 main jets
* 2.5" PV front, rear blocked...vacuum at idle is around 6-7" in neutral, 5" in gear.
* Mixture screws have been all over, car seems to like them between 1-1/4 and 1-1/2 turns. Given the situation, I run them at 1-1/2.

combo:
* 428 + .060 Pontiac (4.181 bore x 4 stroke)
* 325cfm (200cc) @ .700" aluminum heads
* 11.25 to 1 CR
* 264/268 @ .050", 296/300 @ adv, 108 separation, installed at 104, .620/.629" gross lift, flat tappet
* victor intake, stock
* 3600rpm stall
* T350, 12-bolt w/3.90 gears, 28" tire.

The problem is that when I approach 2000rpm & cruise @ 40-45mph, the engine will (at least i think) go lean and start to misfire. typically, it will also start to raise the water temp. it idles perfect. WOT seems to be good too. I've tried adjusting the idle mix screw from 1 turn all the way to 2 turns. no effect at all and the car won't stay idling.

i recently checked the float levels, and they are right at the bottom of the sight plug. it seems the general feeling is that the booster isn't pulling enough fuel during the 2000-3000rpm range. maybe it's the victor? i'm going to run the float a touch higher, maybe that will help.

[stickboy]

I'd try jetting the front up, sounds like you just go lean as the main circuit comes in.

Or....Too much timing at cruise? Vacc advance or no?

Spacer? Might affect it?

Just throwing out stuff.

I also squared up the idle circuits front to back, seemed to help dial it in. IFR's and IAB's. The sec side had smaller IAB's, don't know what you have - you said the fronts were 67.

[formulabird428]

no spacer. considering a 4-hole one. mech advance. timing 16 initial, 30 total @ about 3000rpms.

i can't believe i'd need more than 82 on the fronts, but i could jet it up.

[Tom Vaught]

I think the T-Slot restriction size is way too small for the size of the camshaft. .060-.080 is typical.

I see you also posted on the Innovate Board. The guy you would want to talk to about the air by-pass mods is a guy named Jeff, "shaker455" on this board I believe. He could describe how to do the mod on the Holley. .172" idle by-pass holes are very large for that size camshaft.

Tom Vaught

[hungry69bird]

i was about to post my similiar situation and still might...but

mine is doing almost the same thing only 2000 too 3000-3200 and its at cruise throttle or even a bit of a very light coast throttle. any light throttle and it seems to go away.

but the more i drive it and it gets warmer it seems to pop and miss more frequently along with a bit of a surge feeling as it gets warmer while its popping and missing..the popping and missing is out the exhaust.

i had over revved mine (brain fart on the reverse valve body and hit neutral insead)..was popping very bad...getting worse after that even at idle, popping very loudly so i threw in some autolites and it seemed like it ran great for a day then started popping worse again so i ordered some more ngk's and put them back in...not as bad but still cant get rid of the popping and miss at cruise...

ran 76 jets front for 2 years no issues....jumped to 80's....miss still there...can smell its a tad rich...but top end seemed to pull harder

car pulls 6700 with out hesitation or miss as long as my foots in it

[guccieng]

thanks guys for the t-slot advice! along with the innovate forums, you guys convinced me to try hacking up a 500 dollar carb (hp street 750 dp). didn't take much with a hacksaw blade to bring the slots down to my almost-closed throttle plates. driveability is better, along with opening up the pvcr and jetting the primaries down, lean cruise is right at 15 afr, 12.5 with my foot in it!

[formulabird428]

Originally Posted by hungry69bird

i was about to post my similiar situation and still might...but

mine is doing almost the same thing only 2000 too 3000-3200 and its at cruise throttle or even a bit of a very light coast throttle. any light throttle and it seems to go away.

but the more i drive it and it gets warmer it seems to pop and miss more frequently along with a bit of a surge feeling as it gets warmer while its popping and missing..the popping and missing is out the exhaust.

same thing here. i just noticed the surge tonight.

[formulabird428]

Originally Posted by Tom Vaught

I think the T-Slot restriction size is way too small for the size of the camshaft. .060-.080 is typical.

Tom, what do you mean by this T-slot restriction? IFR?

[formulabird428]

i also have a set of unmodified 4781-3 metering blocks. would these blocks happen to be "superior" to my 80509 (but one of the older version) blocks?

[shaker455]

Zach,
Trailer your car out here for a weekend and I will teach you how to modify, tune & address your cars cooling issues.
Jeff