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Holley Carb issues

Old 11-15-2020, 06:39 PM
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Default Holley Carb issues

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?
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Old 11-15-2020, 07:01 PM
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for the record, not my first holley, however the first one that has me stumped
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Old 11-15-2020, 10:59 PM
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Probably not the answer youíre looking for...

Can you try using Holley parts versus the Pro Comp stuff? Iíd think the Holley parts would be better. I think thatís where your probably may be.
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mike tkach (11-16-2020)
Old 11-16-2020, 06:38 AM
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have not had problems with PCE in the past.

the issue is tuning and the interaction with the LSAB, IFR and the throttle bypass size in the blades.

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Old 11-16-2020, 07:34 AM
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Just got mine back from Pro Systems in Michigan , Patrick did an Awesome job


https://www.prosystemsracing.com/
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Old 11-16-2020, 09:45 AM
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There is obviously a fuel restriction in the idle circuit. I would pull it apart and throw it a can of carb cleaner and let it soak and then blow everything out backwards. Could be anything, dirt, piece of gasket, machining burr. My buddy has a speed shop and he was running into something similar and ended up finding a piece of cellophane rolled up inside one of the legs of the brand new feed line to the carburetor. Try trouble shooting that one. I have a Pro-Systems carb as well and it took me forever to get it right.
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Old 11-16-2020, 09:58 AM
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Saying this straightforward with no emotion...Yeh, hard to say when you have old junk parts and, other than The new holley parts, new parts from a known Junk parts maker.

Check for flat sealing surfaces, correct gaskets, gaskets that donít close off holes, holes in fight position,!and somehow find out what all passages, restrictions, and etc are supposed to be and check those.

Be interesting, and good info on what ends up fixing it.
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GLENAMY 242SS (11-16-2020)
Old 11-16-2020, 10:25 AM
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Following along on this one. I have a very similar issue going on with a holley carb that I have posted in the DIY section.
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Old 11-16-2020, 10:47 AM
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I'm assuming the engine ran fine before installing this carb? I didn't see in the posts if the engine was checked for a vacuum leak.
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GLENAMY 242SS (11-16-2020)
Old 11-16-2020, 05:16 PM
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engine runs fine with the 715, just has performance issues in a few areas as noted (upper end breathing and load pickup from lack of second squiter)

there is no vacuum leak. checked with a can of WD40 and an un-lit propane torch and the only way there could be a vacuum leak would be the main body to the throttle plate joint which would be impossible.

this is a tuning issue with the 5-jet off-the-shelf metering block that needs to be tuned to the application.

the carb is spotless, after soaking the carb when I got it, each and every passage was chased with fishing line and sprayed out with carb cleaner and then using a flashlight, looking thru the drillings to verify no debris there is no restriction in any of the passages, and yes, I even pulled the metering blocks apart and looked in each passage to see if there were machining burrs in any of the jet holes. being that this is an HP series carb, there are very few drillings in the main body, 4 for the HSAB, 4 for the LSAB, 4 for the idle circuit, 4 for the transfer circuit, 2 for the squirters and 2 for the power valves. the throttle plate has the 4 idle circuit holes going to the transfer slots, the 4 transition holes

could there be a bit of dirt in a single idle circuit, possibly, however all 4, extremely unlikely

the gasket surfaces were all checked with a machinist straight edge and feeler gauges, other than the original staking of the dog legs, flat as can be. actually flatter than the last GM motor deck I worked on. I also checked the throttle plate against a plate of glass.

now, here is what I believe is happening, especially since I can get it to idle by partially blocking the LSAB's which enriches the idle

the PCE 2-circuit block has 5 emulsion tube jets on each side and the aforementioned IFR jet at the top of the . that would make it extremely sensitive to fuel level and tuning. I also drilled the holes in the throttle blades about .007 under (0.094 vs .100)

What I am looking for is confirmation and tuning tips. I believe I need to block off the top 1-2 emulsion tube jets or play with the arrangment, and possibly up-size the throttle blade by-pass hole.

the up-sizing of the bypass hole would allow increased air flow, thus increasing the idle signal across the transfer slots with the blades closed. again, I am looking for confirmation. I dont want to drill too large a hole and need to start over.

the blocking of the emulsion tube is based on some reading relating jet/plug placement and fuel level and its impact on idle quality.

the suggestion was from one of the guys
1 emulsion hole .028
2 emulsion hole plugged
3 emulsion hole .028
4 emulsion hole plugged
5 emulsion hole .028

I am looking for tuning suggestions for the parts I have.

doing some further digging, I may need to open the IFR from what may be 0.028 to about 0.035-0.037. However I should verify that an emulsion bleed and a plug didnt get mixed into the IFR ports

again, I am looking for tuning suggestions and if you have links to useful tech articles, that would be great.
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