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Holley Carb issues

Old 11-16-2020, 06:23 PM
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Racingfuelsystems.com is a great carburetor tuning resource. Whitmer, tuner, yeti and some others very sharp.
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Old 11-16-2020, 06:54 PM
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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.

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Old 11-20-2020, 01:29 AM
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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.
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Old 11-20-2020, 07:06 PM
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Originally Posted by mcollinstn View Post
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.
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Old 11-20-2020, 11:00 PM
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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.
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Old 11-21-2020, 11:11 AM
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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.
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Old 11-21-2020, 02:43 PM
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Is the base plate set up for 4 corner idle?
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Old 11-21-2020, 05:51 PM
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Originally Posted by fbc25el View Post
Is the base plate set up for 4 corner idle?
yes
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Old 11-21-2020, 07:28 PM
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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?

Last edited by fbc25el; 11-21-2020 at 07:30 PM. Reason: Added stuff
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Old 11-21-2020, 08:11 PM
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Iím still banking on using actual Holley parts vs known to be problematic pieces from PCE. You have a Holley carb thatís now bastardized.

You have a basic engine combination that should run off a box-stock Holley 800-850. You shouldnít be diving into all this to get it to run properly.

Pick up a real Holley carb and Iíll bet your issues will go away.

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