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calling all holley carb gurus

Finally splashed the boat this year. however due to budget constraints, I used the 715CFM Holley vac-secondary carb I had. Motor is a 468 BBC with Merlin heads, RPM air-gap intake, Stainless Exhaust with custom pipes

idles great, however needs more on the upper end, and being a single squirter, the hole shot would bog a bit when the secondaries opened if i mashed the throttle

so....fast forward after 30 hours and a few dozen splashes or so on the motor.....time to upgrade the carb.

ebay special, early gen 1 950 HP (date code 3186 - meaning November 13th, 1996) this is just before they went with changeable air bleeds

picked the carb up, discovered the secondary metering block was incorrect for a 4-corner idle carb and the throttle shafts and blades were butchered. mis-matched squirters and an odd staggering of main jets...... i called the guy up to get a refund or make it right. so after getting partial refund

2 new pro-comp billet metering blocks, a Holley /Quick fuel throttle shaft kit and new blades and I have the carb cleaned, painted, and back together
6.5 power valves, #80 jets on all 5 corners, stock emulsion jets in the pro-comp block

now, here is the issue

i can not get the carb to idle.
secondary air transfer slot is showing about .020", primary about .030
idle screws starting at 1 full turn out on all 4 corners
adjusting the 4 screws did nothing
motor will run 2000 rpm or higher, however will not run on the idle circuit

if I sit there with my finger on the accelerator pump and tweek the pump just a bit, i can get it to idle. that tells me its not pulling fuel from the idle circuits

if I put my fingers just above the air bleeds on the throttle horn, I can get the motor to idle.

that tells me that either the pro-comp metering blocks have an issue, maybe with the IFR jets, or there is something else wrong.

the outer 4 air bleeds measure stock at 0.070"

any suggestions?

for the record, not my first holley, however the first one that has me stumped

Just a first impression- - - -the bleed holes in the throttle plates look WAAAYYY too small for an engine that big, causing the idle speed screws to have to be turned in enough to interrupt the vacuum on the idle ports. On round track race engines with radical cams, it was not unusual for us to have to open up the bleeder holes in the throttle plates to let the blades close far enough to make the idle circuit work.
Jerry

Jerry, the original blades on the motor had holes that were .100, I drilled out the new blades .094 and then chamfered them I can open them up a bit.

any thought to maybe needing to change the LSAB's to something just a touch smaller?

Air bleeds operate in inverse proportions to jets- - - - -smaller is "richer". Dad used to adjust main jet mixture on his alcohol/peroxide fueled round track car by changing main jet air bleeds, since the jets had been drilled out so far they tried to break off when they were tightened firmly. He was using a big 2-barrel Zenith carb for a Mack truck on a 300+ cubic inch flathead V8, and flowing more air than his competitors with 3 Stromberg 97's.

I have a sneaky suspicion you're over-carbureted. Have you considered using a Quadrajet for a 500 cubic inch Cadillac engine? It flows over 800 CFM, and the secondary air valve prevents bogging when the throttle plates are dumped wide open. I got 714 HP at 6500 RPM from a 460 cubic inch MOPAR 440 truck pull engine, running one of those carb- - - - - - real dyno numbers, not pipe dreams conjured up while bench racing!
Jerry

boat motors tend to be over-carbed, primarily for the holeshot, and the upper end

the beauty of the 950HP is it only flows about 850-870 CFM. it the base plate from the 850 and higher with the 1.75" throttle blades and the upper venturies of a 750 with the 1.375 venturi bores


the motor will use every bit of the carb

the old 715 CFM was what came stock on the 350 small block, other than re-jetting, changing the squirter and vac spring, while it ran on the 468, it was a bit small.

what is confusing me is I can get it to idle grea by partially blocking the LSAB's or fully blocking the HSAB's I believe the billet metering block needs tuning with the IFR jets and I may need to adjust the LSABs

Good luck- - - - -a Q-Jet just bolts on and works- - - -Holleys are "almost right- - - -some of the time".
Jerry

Talked to holley's tech line for a while. the guy said start by restricting the LSAB's since my carb is an early HP, that means epoxying the holes shut and re-drilling (or drill and tap for changeable jets). he suggested going down from the .072 that are supposed to be in there to closer to .040 or .050.

then open the throttle plate bypass just a bit.


A Q-jet needs a calibration kit of rods and bits.....

So talking to a few of my gearhead friend, they suggested looking at the IFR's. they speculated the IFR on the speedmaster block was way way too small. this is something where very minute changes effect the idle AFR in a serious swing. the Speedmaster/PCE metering block has only .0225" orifices on the emulsion tubes and the IFR. at a minimum the IFR needs to be at least .031 per the Holley and Demon documentation I have, preferably closer to .035" at .0225, that is only .0004 square inches vs .0010 square inches. that means they are only 40% of the size they need to be. no way the stock Speedmaster metering blocks will support more than a V6 at idle with stock IFR jetting they have in the blocks. Talked to the folks at Speedmaster in Cali twice, may as well call my local politician. the block itself may be usable, however the block assembly is a joke and there is no support from Speedmaster/PCE. they simply know nothing, and will not return calls

Drilled out the main body LSAB's and HSAB's and threaded for #10-32 standard air bleed jets. however local speed shop did not have any stock on the emulsion jets or air bleeds, so off to the hardware store in the AM to buy some screws to modify. will most likely get brass set screws and drill with the pin-vise in the AM

will attempt to drill out the Speedmaster jets and see where that goes, Will also pick up a few #6-32 screws. going to mimic the Race Demon setup for an 850 on the IFR and emulsion tube jets. however if that doesnt work, I already found a replacement stock 950HP rear metering block

Will report back when I get the carb back together. the new main body gaskets finally showed up.

closing the loop on this

order from Summit finally showed up on Friday. removed all the speedmaster/PCE jets

starting with the IFR, changing from the .0225" to .033"
changed the VPCR's from the .0225 to .059
changed the e-jets from all .0225" to
E1 - .035
E2 - blocked
E3 - .033"
E4 - blocked
Ef - .031"

HSAB's at .032
LSAB's at .059

bolted the carb on, and after priming the fuel system, turned the key and it was idling at 800 RPM

adjusted the 4 corners, and it will idle down to about 700. ended up going to .061" on the LSAB's just to lean out a bit more

now, to drop it in the water to load it