Dominator - can't even get it to idle

[GRTfast]

Sounds like trash in the needle, or a stuck float.

[enigma57]

2 circuit versus 3 circuit metering...... I see you have a 2 circuit Dominator on a mildly cammed road car. I recall hearing mention of mods to make the older 2 circuit Dominators into 3 circuit metering to help with drivability. That was a long time ago and I cannot recall the details now. But I'm sure others here will be able to help if you need to explore that option further.

Hope this gives you some ideas,

Harry

Actually the other way around Harry. Three circuit carbs have a serious issue of part throttle over rich conditions followed by over lean conditions on the top end. The intermediate circuit has it's own feed directly from the float bowl and depending on the feed tube placement, draws fuel early in the metering. This is what causes the overrich part throttle problem. The overlean top end is caused from the idle feed tube being in the main well limiting it's capacity. Even with the jets removed entirely, it's difficult to get enough fuel to feed the engine. Converting a three circuit carb to a two circuit fixes these issues, makes the carb more drivable and much easier to tune. I've done the conversion and it was night and day difference. Two circuit is what you want, not the three. Newer design metering blocks removed the idle feed tube from the main well and gave it it's own circuit, which has helped, but the placement of the intermediate was never changed. Two circuit carbs have never fed the idle circuit from the main well, so that problem doesn't exist. It's also better to relocate the idle feed restrictor to the bottom of the metering block instead of the top like Holley has it, as this cures erratic idle mixture/tuning issues.

On custom aftermarket three circuit carbs, they relocate the intermediate so it's not active as soon, and have improved metering of the transition and main circuits so the part throttle issue isn't an issue anymore. They have also removed the idle feed tube from the main well and all use custom metering blocks....

Thanks for explaining that, Mark. Most of my experience with carburettors has been with Webers. Whole 'nuther ballgame. Have tinkered with non-Dominator Holleys a bit, but I'm not up on the eccentricities of Dominators. Appreciate the info.

Thanks Harry, yeah I actually have tried advancing the timing and retarding. As I can't get it running (even to idle) a lot of my timing activity is pure guess work. When i did get 3 mins of run time before the garage filled with black smoke it was 16 degrees. But I've retarded since then, will add a bit more in.

I'm 10.7 : 1 compression with mild cam (no specs but I know from 5,000 miles of driving on it that it's not lumpy)

Historically (old 3 circuit super rich carb) I'd get 8 In/Hg of manifold vac at idle.

I'm reluctant to drill the blades. i know that is an option. But my view is that I should be able to dial this in using the carb.

I'll try some more timing tomorrow

Hang in there, Freddie. You'll get it sorted. Lots of knowledgeable people and good info here. I do think you'll find after sorting all else that drilling the throttle blades will be necessary. Keep us apprised of your progress. Interesting project. Looking forward to learning more about Dominator carbs.

Best regards,

Harry

[Freddie]

Thanks again everyone.

Just about to pull the carb and go over ever passage make sure there are no blockages

Thought before I do that let me check float bowls

Primary can get it down to about 60% of way up sight bowl but can’t get it any lower. Cannot get it to half. No matter how much I turn adjustment screw

Secondaries. I thought it was half. Turns out I can see the bottom of the float. It won’t adjust down at all

Never had this issue before. Pulling carb now

[norm]

You can take the floats out and bend the tab up on the float arm to get more adjustment on the needle and seat.

Unless it has the old brass floats that is.

I start out with the float level with the bowl upside down or even lower, then adjust after on engine.

[Freddie]

Doing that now. Quick fuel plastic center hung floats

[jmarkaudio]

OK Freddie, some good and not so good info here. Are the metering blocks blue? You may have a methanol carb, the only QF 1150 that is 2 circuit is a methanol carb.

[Freddie]

Mark, no they are red.

Actually QF does make a gas 2 circuit.

Specifically, the one I have is this one

https://www.holley.com/products/fuel_sy ... -4711-2CIR

[jmarkaudio]

Something newer Holley is doing, it's not listed in the spec chart I have. 45 is small for an idle bleed, but depends in the idle feed restriction size. I have built a lot of QFX bodies until Holley quit selling bulk parts to smaller shops, with the idle feed moved to the bottom (require threading the metering block) and threading for adjustable t-slot restrictions it will take a .042 idle feed, .055-.063 t-slot restriction, and idle air from .057-.070 range depending on the engine. Requires 6-32 x 1/8 brass set screws, 10-32 x 3/16 brass set screws, and bottoming taps in both sizes. All can be had at McMaster-Carr, if you are not up for it I can do it as well. Where are you located?

[Freddie]

Mark,

Thanks. Wow, yeah starting to push my skill limits there.

I did change to a 75 IAB and bumped the IFR from 0.037 to 0.035. IFRs are in the top of the metering block (that's where the originals were)

My challenge now seems to be float adjustment. So just trying to solve that first.

I also may have had T-slot closed up a tad too much, more like 0.10 not 0.20. I opened it up to 0.20.

Will get the float issue sorted then fire it up see if I can at least get it to idle.

[ClassAct]

2 circuit versus 3 circuit metering...... I see you have a 2 circuit Dominator on a mildly cammed road car. I recall hearing mention of mods to make the older 2 circuit Dominators into 3 circuit metering to help with drivability. That was a long time ago and I cannot recall the details now. But I'm sure others here will be able to help if you need to explore that option further.

Hope this gives you some ideas,

Harry

Actually the other way around Harry. Three circuit carbs have a serious issue of part throttle over rich conditions followed by over lean conditions on the top end. The intermediate circuit has it's own feed directly from the float bowl and depending on the feed tube placement, draws fuel early in the metering. This is what causes the overrich part throttle problem. The overlean top end is caused from the idle feed tube being in the main well limiting it's capacity. Even with the jets removed entirely, it's difficult to get enough fuel to feed the engine. Converting a three circuit carb to a two circuit fixes these issues, makes the carb more drivable and much easier to tune. I've done the conversion and it was night and day difference. Two circuit is what you want, not the three. Newer design metering blocks removed the idle feed tube from the main well and gave it it's own circuit, which has helped, but the placement of the intermediate was never changed. Two circuit carbs have never fed the idle circuit from the main well, so that problem doesn't exist. It's also better to relocate the idle feed restrictor to the bottom of the metering block instead of the top like Holley has it, as this cures erratic idle mixture/tuning issues.

On custom aftermarket three circuit carbs, they relocate the intermediate so it's not active as soon, and have improved metering of the transition and main circuits so the part throttle issue isn't an issue anymore. They have also removed the idle feed tube from the main well and all use custom metering blocks....

Thanks for explaining that, Mark. Most of my experience with carburettors has been with Webers. Whole 'nuther ballgame. Have tinkered with non-Dominator Holleys a bit, but I'm not up on the eccentricities of Dominators. Appreciate the info.

Thanks Harry, yeah I actually have tried advancing the timing and retarding. As I can't get it running (even to idle) a lot of my timing activity is pure guess work. When i did get 3 mins of run time before the garage filled with black smoke it was 16 degrees. But I've retarded since then, will add a bit more in.

I'm 10.7 : 1 compression with mild cam (no specs but I know from 5,000 miles of driving on it that it's not lumpy)

Historically (old 3 circuit super rich carb) I'd get 8 In/Hg of manifold vac at idle.

I'm reluctant to drill the blades. i know that is an option. But my view is that I should be able to dial this in using the carb.

I'll try some more timing tomorrow

Hang in there, Freddie. You'll get it sorted. Lots of knowledgeable people and good info here. I do think you'll find after sorting all else that drilling the throttle blades will be necessary. Keep us apprised of your progress. Interesting project. Looking forward to learning more about Dominator carbs.

Best regards,

Harry

You do not set the power valve opening by idle vacuum. This is wrong. Mark W has posted a video to you tube proving the power valve won’t open at idle.

[Freddie]

OK, good news. Got it to idle at a touch over 1000 RPM.

Pulled carb apart and blew air through every single orifice, hole, tube etc.

Cleaned everything.

Checked T-Slot found it to be a tad too closed. Opened it up to 0.20

Changed IFR's from 0.037 to 0.035.

Went back to 75 IABs.

Re-installed carb, found float levels all over the place. Had many attempts but got them at half level of sight bowl.

idle mixture screws. Tried at 2 turns wouldn't run
moved out to 2.5 turns

Now it fires and starts without me touching the pedal...woo hoo.

Only pulling 6 in/hg of vac

I turned mixture screws in half a turn to 2

did not tune, as new build so want rings to seat. Let it run for about 3-4 mins at 1020 RPM.

But had to shut it off, it's not as bad as it once was, but it's still super rich so much so my eyes were burning.

so I'm guessing at this point all else being equal my options are:
1. go an even bigger IAB to lean out the idle circuit some more (and possible close up the Tslot just a touch if I do...or leave as is)
2. pull the metering blocks and go an even smaller IFR

at this stage I have not hit the gas pedal, just let it idle.

My off idle AFR is yet to be explored in any way, that will follow once I get idle clean.

I am not using an O2 senor this is old school, ears, eyes, nose and vac gauge.

[enigma57]

Making progress.

Good on you,

Harry

[1980RS]

I'm at a bit of a loss.

Newly rebuilt engine.

2nd hand carb - but barely used.

632 BBC Checv. Mild cam.

QFT 1150 2 circuit dominator.

On my own, no helpers. Cant get it to run. Moment I take my foot off the pedal it stalls.

It came jetted 84 / 92
IABs 45
HSAB 33
PV 3.5 primary
PV blocked secondary

I can get it to run but stupidly rich by opening up the transfer slot (curb idle) and letting lots of air flow in, but it fouls the plugs in 5 mins and I can't handle the putrid black smoke, it's crazy rich.

What have I tried.

1st I set the transfer slot to exactly 0.020 (measured with a feeler gauge). Since I have done that I have NOT touched the curb idle

Jetted primaries to 80 and secondaries to 84
I know these should make no difference to idle.
but off idle (no fuel from the boosters, just the transition slot it's still crazy rich
I also installed 2.5 PVs primary and secondary (this is a street car so PV's will help) it also always had low Vacumm when it was running last.
FYI - old carb was a POS non adjustable. that fouled plugs all the time. That ain't going back on.

Then I changed Idle air bleeds to 55, 65 and 75. I also wound out idle mixture screws from 2 turns to 3 1/2 turns (with each of the different air bleeds).

Regardless of air bleeds and mixture screw settings, it always did exactly the same thing

1. I have to keep my foot on throttle to open up the primary blades (I'm running a progressive linkage), so no fuel coming out the boosters, but it does expose the transition slot and pulls fuel through that. It will sit nicely on 1100 rpm with my foot resting on pedal primary blades open. Note at this point it's still incredibly and crazy rich, spitting unburnt fuel out the exhaust even at just 1100 RPM. Moment I take my foot off gas it drops to 500 RPM and stalls, instantly
2. I tried removing the idle air bleeds completely so it would have gulps of air...backfired out the carby, so I know it's too much air

so my issue is I cannot even get it to idle at all, literally can't step away from the gas pedal, and still stupid rich when low rpm.

I have idle feed restrictors but I've never changed those before.

My guess is it needs more air, not more fuel.

You may be thinking float level or fuel pressure.

Fuel pressure I filmed gauge while I had my foot on gas, it's good at 6PSI
Float level, neve had car run so I can't get to it. But wit it stopped and pump on I have set it to just above bottom of sight bowl.

Thanks in advance for any advice you might be able to offer.

Typical QF run out of Fuel Quickly. If you were close to me I would let you try my Holley 1150. IMO that QF will need to be completely re-calibrated to your combo. Years ago I bought a BLP 1050 from a very good racer I've known since high school. He had the BLP and a BG King Demon, I called BLP to ask if it was really on of theirs, gave him the number on the main body and yes it it's one of ours. He asked what I paid for it and I replied $200 for it, the guy wanted $500 for the King Demon. The BLP fellow said you saved yourself $300 and a bunch of tuning headaches.

[enigma57]

You do not set the power valve opening by idle vacuum. This is wrong. Mark W has posted a video to you tube proving the power valve won’t open at idle.

Thanks, ClassAct. Yes, I remember those discussions here some years back. Always interesting.......

viewtopic.php?f=1&t=14523&start=15

One school of thought was for setting power valve as per Holley's recommendations (idle vacuum in neutral if running a stick or idle vacuum in gear if running a slush box). Other school of thought was for setting power valve by manifold vacuum at cruise with car in motion on highway. And others simply said in so many words to experiment and give your engine what it wants. I have tried all of the above with non-Dominator Holleys and each methodology has merit.

Another reason I enjoy tinkering with Webers. The series I work with most has only one variant which runs a power valve and there are no varying sizes. Just the one. The remainder have no power valve and must be jetted accordingly when reconfigured to run on plenum intake rather than IR intake.

Best regards,

Harry

[Firedome8]

Actually the other way around Harry. Three circuit carbs have a serious issue of part throttle over rich conditions followed by over lean conditions on the top end. The intermediate circuit has it's own feed directly from the float bowl and depending on the feed tube placement, draws fuel early in the metering. This is what causes the overrich part throttle problem. The overlean top end is caused from the idle feed tube being in the main well limiting it's capacity. Even with the jets removed entirely, it's difficult to get enough fuel to feed the engine. Converting a three circuit carb to a two circuit fixes these issues, makes the carb more drivable and much easier to tune. I've done the conversion and it was night and day difference. Two circuit is what you want, not the three. Newer design metering blocks removed the idle feed tube from the main well and gave it it's own circuit, which has helped, but the placement of the intermediate was never changed. Two circuit carbs have never fed the idle circuit from the main well, so that problem doesn't exist. It's also better to relocate the idle feed restrictor to the bottom of the metering block instead of the top like Holley has it, as this cures erratic idle mixture/tuning issues.

On custom aftermarket three circuit carbs, they relocate the intermediate so it's not active as soon, and have improved metering of the transition and main circuits so the part throttle issue isn't an issue anymore. They have also removed the idle feed tube from the main well and all use custom metering blocks....

Thanks for explaining that, Mark. Most of my experience with carburettors has been with Webers. Whole 'nuther ballgame. Have tinkered with non-Dominator Holleys a bit, but I'm not up on the eccentricities of Dominators. Appreciate the info.

Thanks Harry, yeah I actually have tried advancing the timing and retarding. As I can't get it running (even to idle) a lot of my timing activity is pure guess work. When i did get 3 mins of run time before the garage filled with black smoke it was 16 degrees. But I've retarded since then, will add a bit more in.

I'm 10.7 : 1 compression with mild cam (no specs but I know from 5,000 miles of driving on it that it's not lumpy)

Historically (old 3 circuit super rich carb) I'd get 8 In/Hg of manifold vac at idle.

I'm reluctant to drill the blades. i know that is an option. But my view is that I should be able to dial this in using the carb.

I'll try some more timing tomorrow

Hang in there, Freddie. You'll get it sorted. Lots of knowledgeable people and good info here. I do think you'll find after sorting all else that drilling the throttle blades will be necessary. Keep us apprised of your progress. Interesting project. Looking forward to learning more about Dominator carbs.

Best regards,

Harry

You do not set the power valve opening by idle vacuum. This is wrong. Mark W has posted a video to you tube proving the power valve won’t open at idle.

I am thinking it will open but not effect the mixture do to pvcr restriction in relation to the ifr.