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?

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

Probably not the answer you’re looking for...

Can you try using Holley parts versus the Pro Comp stuff? I’d think the Holley parts would be better. I think that’s where your probably may be.

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.

Just got mine back from Pro Systems in Michigan , Patrick did an Awesome job


https://www.prosystemsracing.com/

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.

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 don’t 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.

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.

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.

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.

Racingfuelsystems.com is a great carburetor tuning resource. Whitmer, tuner, yeti and some others very sharp.

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.

Might be a good time to drill and tap the LSAB holes for 6-32 brass set screws that you can drill and change out instead of the pressed-in orifices.

Here's some if the stuff that doesn't sound right...
The throttle plates ought not be exposing the slots at idle.

You have the 4 corner screws only out 1 turn? Go ahead and open them 3.5 turns out and see if that gets you anywhere close to an idle. I wouldn't think you need to be drilling the throttle plates yet..

Here is what I would try before you go nuts on modifying the carb..
If you have a carbureted car (or a buddy's car) with a wideband O2 sensor on it, then bolt this carb on it and start homing in on getting the idle feeds and bleeds sorted out. Once you get a good idle on "motor x" you can go back to
the boat and keep making progress.

The body to baseplate needs the correct gasket and both surfaces need to be lapped flat. Seen plenty of holleys with warped baseplate.

Be sure you aren't leaking vacuum somewhere.

As far as the smaller carb, you should be able to tune out any bog on a holley vac secondary. Pump sizes, pump cams, lever ratios. nozzle sizes, secondary springs/weights. I suppose there may be a combo out there that you can't tune out the bog, but I'd have to see it to believe it.

But really, bolt the carb on a motor with widebands so you can monitor afr and start systematically diagnosing it all.

Remember, for idle you should not have the slots uncovered. Idle screws, feed ports, lsa bleeds, float level, and clear bowl vents all control idle fuel.

Thanks for the feedback.

I went out as far as I could turn the idle mix screws before them falling out. no joy, just simply not responding to the idle mix screws unless I partially blocked the LSAB's.

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.

Big tipoff of the idle feed restrictor suze is when you said turning out more didn't do anything.

BUT its difficult to make the idle feed Smaller, so you really are better off with easily adjustable LSABs so you can creep up on getting a decent idle (with smaller LSAB), and THEN watch the curve as you expose the transition slots right off idle.

An AFR meter is invaluable for bleed and transition diagnosing. Can be very frustrating without one.

the IFR's need to go bigger, so simply drilling them out will work. with the IFR's, slight increase in size increases fuel. opposite of the LSAB, which is decrease in size increases fuel.

Is the base plate set up for 4 corner idle?

yes

I would try it with out holes in the throttle plates. Emulsion is when the boosters are active. That still is a lot of it. Does it also have a kill bleed?

I’m still banking on using actual Holley parts vs known to be problematic pieces from PCE. You have a Holley carb that’s now bastardized.

You have a basic engine combination that should run off a box-stock Holley 800-850. You shouldn’t be diving into all this to get it to run properly.

Pick up a real Holley carb and I’ll bet your issues will go away.

I never had any issue like this with out of the box new carbs (950hp blower motors)
I mean "ebay special" so you saved a few bucks and now it doesn`t work and you have to spend all this time and work to get it to work right ?! I would have thrown it in the garbage long ago .
Being cheap never works out .

Holley QuickFuel 850 Marine on sale now from Holley $673.13
I can't believe it took this long for somebody to finally break the egg.

I know the issue is the PCE metering blocks. thats a given.

the issue with them is the IFR and emulsion jets are too small. comparing them to the QFT blocks at the speed shop, they look to be a copy of the QFT blocks other than the jet sizes.

since the jets are undersized, I have a bag of jets coming along with a bag of air bleeds.

yes the blocks have the siphon breaks (or kill bleeds)

With the current price of Holley sniper efi, I don’t think I’m ever going to mess with a carb again. Been down this road many times. Really sucks when you need to save money but it ends up costing more

not going to go EFI, even if it was free. the amount of knowledge that I have gained over the past 3 weeks on fuel system tuning has been invaluable.

why not? I’ve done a ton with carbs, built my own blow through setup, nitrous, roots blowers etc. so many benefits to efi that if the price point is close I have no reason not to.

1) Your still dead in the water trying to figure out a misfit/ miss matched holley carb... even if you do get it figured out - how reliable is the fix until the next problem? This thread is on page 3??

Play devil's advocate and pay yourself an hourly rate (Same as a service shop) for the BS head scratching you are going through and the cost of a tow call... a NEW carb may be the cheapest/ most reliable and safest long term fix. I am not soap boxing as most everyone has tried to make a carb work for the money but, there comes a time when the garbage bin is the proper course of action

2) Why knock EFI? It's simple, adaptable to most power levels and the kits work.... plus the fuel metering calibrations if properly set actually help the longevity of the engines.

My $0.02

because 100% of fuel injected motors have left me stranded on the side of the road over the past 1.5 million miles and 40 years boating. only once did a carbed vehicle leave me stranded, and it was the ignition trigger

BTDT with EFI systems on motors since the mid 80's, every one failed for one thing or another resulting in a tow, and in two cases, waiting on the side of the road for over 10 hours until the tow truck showed up because a failed cam sensor or a failed knock sensor. only once have I had a carb'd motor fail where I could not get it going and that was the ignition trigger in a mallory dizzy. now I carry a spare in the boat along with the tools to fix it. I have even drove 25 miles home with a failed mechanical fuel pump on my old mud truck by rigging up a gravity feed system for the carb using a cooler, my tee shirt and a pocket knife and cutting the fuel line from under the vehicle.

even the new vehicle of the wife's is on the 2nd throttle pedal, throttle body and throttle controller and the vehicle only has 45k on the odometer

not knocking EFI, built plenty of projects with everything from Westers tuned GM ECM's to holley DFI to megasquirt to 034 Motorsports EFI over the years. Just dont want it in the boat.

as stated prior, awaiting the new pack of air bleeds and emulsion jets from Summit to show up so I can see how the carb responds to the opened up IFR, PVCR and Emulsion jets.

I have to stand up for my fellow carb runners. I have a high compression, big cam motor that runs like a dream with a carb. I don't have a wide band so I have been gradually backing down jets and using an Otoscope to check plugs to make sure I haven't gone to far. I also have to admit I am running a Daytona Sensors ignition that has idle control through digital timing control. I don't have a choke and I boat in some very cold weather. My boat starts great, idles great and I can cruise down the river for an hour at 650rpm. Actually once it's been started once for the day, it's the fastest starting vehicle I own. I once ran my batteries down so my starter would only bump over one compression stroke. All I had to do is give the throttle a little bump and hit the key as quick as I could and that baby started right up. Try doing that with EFI. All one has to do is read the forums and the plethora of issues with EFI. I am an EFI guy, I have HPTuner software and have tuned almost all of my vehicles. I have installed EFI on one of my hot rods and yes I got it to run great. But then again so does my carb and it gets great fuel economy and fewer parts to go bad. All you need is a spare fuel pump and your good to go.

Dudes been trying to fix a pile of junk carb for a month and says EFI is unreliable , classic! :lolhit:

EFI blows carbs away in every category especially in boats. Sorry, not sorry.:noevil:

I personally like the simplicity of a tuned carb, BUT, screwing with a pile of old hacked together junk is a waste of time in my book. $700 and be done with it. Tons of tuneability with the new QuickFuels.

If he got junk parts and mismatched parts for an EFI system, that would have issues too.

So, I would suggest this thread is not carb vs efi, but one about junk ProComp/Speedmaster/SSI (sll same fraudulent and horrible makers of parts) thrown onto something that is mot working correctly as it was.

So, I’m just sitting back and watching the trials and tribulations of this one off messed up carb project.

Hate to bust your bubble there bucky but you won't make an ounce more HP with EFI than with a properly set up carb. (Provided you know how to tune a carb.)
EFI will usually start easier and there are some gains to be made in part throttle fuel consumption and the ability to closer monitor fuel for torque gains thru the rpm range. But if you really think that a carb can't compete...

You stick with your carbs then bucky .
I know better .

Neither EFI or Carb can make more power for a given combustion mix. been proven thousands of times on dynos.

enough with the bashing guys. Its not that I have been trying to fix a carb for a month since this thread only started 8 days ago and 4 of those days were weekends when nothing is going to ship until the following monday, and 2 of those days I was recovering from surgery. I can guarantee I have learned more in the past 8 days on carb tuning and how PVCR's IFR's LSAB's and HSAB's effect the fuel curve. that is knowledge that will remain with me forever

no such thing as a "good out of the box one-size fits all carb" Especially a Holley or QFT you can get close with a custom ordered Demon, however that is well over $700. buy a custom built carb to match your exact specs and you are well over $1500.

I went the route of buying a used carb and other than the incorrect jet sizing on the PCE metering blocks requiring a few different size jets, It will get tuned for my motor by me. to those that helped, thank you.

I have a couple 1000hp blower motors turning 18" diameter props that bite hard. (you gotta have the tune on point otherwise it dies during a shift .
I`ve spent a considerable amount of time, as in a 4-5 seasons, trying to get the curve right . watching and recording AFR`s and making constant adjustments with air bleeds, jets, power valves, boost referenced , non boost referenced etc. If I had a dollar for every weekend I was in the bilge with my hands full of fuel changing jets I`d have a lot of dollars. Most people who think their carbs are so great never even know what AFRs they are running. They set a good idle , check plugs a few times and off they go . probably easier to be ignorant of it honestly.
While it idled like a 500 EFI and ran great the fuel curve was never good no matter what. The nickerson "custom" carbs I got rid of were even worse and they were $1500 carbs .

I could go into how EFI is constantly compensating to have a perfect fuel curve at all times, how the IACS and timing control idle , how I don`t have to run in the low 12`s at idle to keep the engines from dying during a shift, how bad it is to be dumping so much fuel at idle in the motors, how I have a bunch safeties set up if anything goes wrong . how easy it is to make changes via laptop, how easy it is to run one bus cable to populate all gauge info, 7" screen that show you everything you can possibly think of .. how the gas savings were pretty unbelievable ..

Try and achieve this fuel curve with a carb at 50* or 99* different elevation , humidity, etc .. you can`t . ever .


https://cimg9.ibsrv.net/gimg/www.off...0d2eca1ee4.jpg


I get it thou, it`s not for everyone...I still have friends that have a flip phone .. but carbs are probably more like a pager vs smart phone.:D


BTW , I never got EFI cause I thought it would give me more power and I also have no idea what HBAS IFR`s LSABs are .. with a good carbs I never had to mess with any of that .

I have done the same Dan, F ing around with jets, and LSAB, HSAB on my procharged set up, yes it runs good but... in my opinion there is a lot of "driveability" left on the table.
I believe EFI is the way to go.
Carbs work ok but EFI is so much better WHEN DONE CORRECTLY.. I think there are a lot of EFI hacks out there adding to the mistrust of EFI. JMHO

Dan,
Do you believe that you have better fuel efficiency with your EFI? Your setups would be a good comparison. You are still throttle body, not port injected right?

Blow thru, personally, I’d fo EFI for sure. Other than big hp big roots/screw sc carbs are just fine. I’m not into tuner carbs.