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Dominator - can't even get it to idle

General engine tech -- Drag Racing to Circle Track

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Firedome8
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Re: Dominator - can't even get it to idle

Post by Firedome8 » Mon Jun 01, 2020 1:26 pm

enigma57 wrote:
Mon Jun 01, 2020 2:41 am
ClassAct wrote:
Sun May 31, 2020 11:33 pm

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.

:D 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
If I remember correctly some webber's reply on fuel being issued from the accelerator nozzle al high air flow to enrich the mixture.
Been awhile since I tuned on IR webers..

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Re: Dominator - can't even get it to idle

Post by Coloradoracer » Mon Jun 01, 2020 2:05 pm

Firedome8 wrote:
Mon Jun 01, 2020 1:26 pm
If I remember correctly some webber's reply on fuel being issued from the accelerator nozzle al high air flow to enrich the mixture.
Been awhile since I tuned on IR webers..
Pretty much any Holley style carb will also have pullover from the accel pump discharge nozzles, especially at WOT. They do make kits to prevent it, but it's just another tuning aid if you can manage it.
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Re: Dominator - can't even get it to idle

Post by Freddie » Mon Jun 01, 2020 8:05 pm

so latest update.

It seems to like timing set at 21-23 degrees initial.

Idles at 1050 RPM

But still crazy rich

Idle mixture screws work a treat, I can take em in about an 1/8th a turn until it dies.

At just before that point it's got 10 in/Hg Vac.

But still crazy rich.

T-slot os good and I have no plans to touch that, as opening that up for more air will only introduce more fuel also, I doubt it's pulling too much from the T-slot (currently 0.20)...so plan to leave as is

Should I go a smaller IFR (currently 0.035)
or a bigger IAB (currently 75s).

Easiest of course to just change out the IABs but next size up I have are 85s which is a massive 10 step jump.

Thoughts?

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Re: Dominator - can't even get it to idle

Post by 77cruiser » Mon Jun 01, 2020 8:37 pm

If you turn the screws in 1/8 turn it must be lean if it dies. Eye burning is lean.
Jim

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Re: Dominator - can't even get it to idle

Post by Freddie » Mon Jun 01, 2020 9:45 pm

Jim, funnily enough yeah I think I'm lean now. No black smoke like before when I couldn't get it to idle, now just ey burning. So I'm too lean now. Bought to go pull some plugs

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Re: Dominator - can't even get it to idle

Post by Freddie » Mon Jun 01, 2020 9:52 pm

Pulled 2 plugs from each bank. So many overly rich start ups completely dry black soot. On the insulator the stray and the electrode. Completely fouled. May need to throw some new ones in before I go much further

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Re: Dominator - can't even get it to idle

Post by Freddie » Mon Jun 01, 2020 10:43 pm

OK here are the plugs I just pulled....needs a new set before I try to figure out a more optimal AFR

Image

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Re: Dominator - can't even get it to idle

Post by Freddie » Tue Jun 02, 2020 2:00 am

New plugs installed. I gave it 5 mins of run time on these plugs and pulled em.

Here's a pic of #2 plug. All the rest are the same

Still smells and eye burning.

Which I thought happens lean, but apparently not. You can get eye burning from rich as well.

so I guess I'm still stupid rich.

Hmm....

Image

Image

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Re: Dominator - can't even get it to idle

Post by enigma57 » Tue Jun 02, 2020 2:07 am

Freddie, I have been following with interest. Lost track of your current jetting, though. Holley lists 92 mains for these carbs if running power valve and 96 mains if power valve is blanked off. Now that you are getting closer with air bleed sizes, you may want to try the larger main jets Holley specs and see how they work with your new air bleed sizes. I'm thinking 75 idle air bleeds and 45 high speed air bleeds as a starting point? FWIW, out of box Holley installs 0.35 primary and 0.37 secondary pump nozzle size. Out of box jetting should give you a starting point or base line to work from.

Sounds as if your initial timing is good. Double check timing to make sure total advance is limited to 36 degrees, give or take 2 degrees either way when all in, though.

Do you have a good (known) carb to try in order to tell whether everything else is OK?

Regarding your priour carb running rich as well...... Is there any indication of ring seal issues resulting from fuel wash down of cylinder walls over time?

Just a thought,

Harry

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Re: Dominator - can't even get it to idle

Post by cgarb » Tue Jun 02, 2020 3:02 am

This is for sure not a float or needle and seat issue? You have checked for fuel dripping from the boosters? Sometimes those foam floats will absorb fuel and get heavy causing problems. If this carb sat for some time the O-rings on the needle and seats can shrink up some which will allow fuel to bypass the needle and seat.

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Re: Dominator - can't even get it to idle

Post by enigma57 » Tue Jun 02, 2020 3:04 am

Firedome8 wrote:
Mon Jun 01, 2020 1:26 pm
If I remember correctly some webber's reply on fuel being issued from the accelerator nozzle al high air flow to enrich the mixture.
Been awhile since I tuned on IR webers.
Firedome8, I tinker mainly with the Weber DCNF carbs. These are designed to be run on IR intake. Have been recalibrating them for use on plenum style intake for some years now.

Pullover at higher RPMs hasn't been an issue with the DCNFs whether on IR or plenum intake. Might be more pronounced with other series Weber carbs, though. Main issue with these carbs seems to be a tendency to lean out at higher revs. Soldering up (or drilling a new) hole or two in emulsion tubes seems to take care of this without making low or mid-range overly fat. Takes some experimentation though. OD and ID of e-tubes matter as much as where holes are drilled and what size they are.

The other issue is when reconfiguring DCNF carbs for use on plenum style intake, the relationship of throttle blades to progression holes requires drilling a hole in throttle blades to allow carb(s) to idle at a reasonable speed (under 1,000 RPMs).

Last year, I managed to come up with several DCNVH variants and they are interesting in that they were designed for plenum intake and have a power valve. Bonus is that there is no need to drill holes in throttle blades and the ones original to Maserati Bi-Turbo have correct choke tube and aux. venturi (booster) size for what I am doing. Emulsion tubes and jetting all need to be changed just as when setting up DCNF carbs for same engine, though.

The 36 DCNVHs used on naturally aspirated 1500cc and 1600cc Talbots and Sunbeams are hard to come by Stateside. The DCNVHs original to '84 - '85 Maserati Bi-Turbo (2.0 litre Euro spec and 2.5 litre US spec) are an ideal starting point for what I am doing but are scarce as well and crazy expensive if you can find them in good rebuildable condition, complete and unmolested. These are sealed in a pressurized box on the Bi-Turbo engine.

Best regards,

Harry
Last edited by enigma57 on Tue Jun 02, 2020 3:12 am, edited 1 time in total.

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Re: Dominator - can't even get it to idle

Post by Freddie » Tue Jun 02, 2020 3:10 am

enigma57 wrote:
Tue Jun 02, 2020 2:07 am
Freddie, I have been following with interest. Lost track of your current jetting, though. Holley lists 92 mains for these carbs if running power valve and 96 mains if power valve is blanked off. Now that you are getting closer with air bleed sizes, you may want to try the larger main jets Holley specs and see how they work with your new air bleed sizes. I'm thinking 75 idle air bleeds and 45 high speed air bleeds as a starting point? FWIW, out of box Holley installs 0.35 primary and 0.37 secondary pump nozzle size. Out of box jetting should give you a starting point or base line to work from.

Sounds as if your initial timing is good. Double check timing to make sure total advance is limited to 36 degrees, give or take 2 degrees either way when all in, though.

Do you have a good (known) carb to try in order to tell whether everything else is OK?

Regarding your priour carb running rich as well...... Is there any indication of ring seal issues resulting from fuel wash down of cylinder walls over time?

Just a thought,

Harry
Harry, thanks for the reply. This is idle only so haven't even got into the main circuit yet. That 5 mins run time was strictly idle.

I have 84 secondary jets with a 25 PV.

Yeah the engine is a brand new rebuild for the exact reason you mentioned, fuel wash. In fact builder said he'd never seen a cleaner intake and bores as it run so rich for 5000 miles. So trying to avoid the same.

I do not have another 4500 carb (a few 4150 style but no other 4500s)

Going to try an 85 IAB tomorrow (75 right now). Clearly still need to lean it out.

Have not checked total timing yet, will do that

Also going to check coil and spark voltage and make sure that's good

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Re: Dominator - can't even get it to idle

Post by enigma57 » Tue Jun 02, 2020 3:11 am

cgarb wrote:
Tue Jun 02, 2020 3:02 am
This is for sure not a float or needle and seat issue? You have checked for fuel dripping from the boosters? Sometimes those foam floats will absorb fuel and get heavy causing problems. If this carb sat for some time the O-rings on the needle and seats can shrink up some which will allow fuel to bypass the needle and seat.
X 2!! And if you have a good carb that is known to run well (doesn't necessarily need to be a Dominator), it should be OK for break-in and to double check all non-carb settings, Freddie.

HB

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Re: Dominator - can't even get it to idle

Post by Freddie » Tue Jun 02, 2020 3:39 am

cgarb wrote:
Tue Jun 02, 2020 3:02 am
This is for sure not a float or needle and seat issue? You have checked for fuel dripping from the boosters? Sometimes those foam floats will absorb fuel and get heavy causing problems. If this carb sat for some time the O-rings on the needle and seats can shrink up some which will allow fuel to bypass the needle and seat.
checked needle and seat on Sun all look good. Can't see fuel dripping from boosters. Will a 4150 square bore go onto a 4500 flange? I've never even asked / looked i just assumed they wouldn't.

I have an excellent condition, known working king demon sitting in the shelf (1000 CFM) I could just as easy throw it on

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Re: Dominator - can't even get it to idle

Post by midnightbluS10 » Tue Jun 02, 2020 3:57 am

enigma57 wrote:
Tue Jun 02, 2020 3:04 am
Firedome8 wrote:
Mon Jun 01, 2020 1:26 pm
If I remember correctly some webber's reply on fuel being issued from the accelerator nozzle al high air flow to enrich the mixture.
Been awhile since I tuned on IR webers.
Firedome8, I tinker mainly with the Weber DCNF carbs. These are designed to be run on IR intake. Have been recalibrating them for use on plenum style intake for some years now.

Pullover at higher RPMs hasn't been an issue with the DCNFs whether on IR or plenum intake. Might be more pronounced with other series Weber carbs, though. Main issue with these carbs seems to be a tendency to lean out at higher revs. Soldering up (or drilling a new) hole or two in emulsion tubes seems to take care of this without making low or mid-range overly fat. Takes some experimentation though. OD and ID of e-tubes matter as much as where holes are drilled and what size they are.

The other issue is when reconfiguring DCNF carbs for use on plenum style intake, the relationship of throttle blades to progression holes requires drilling a hole in throttle blades to allow carb(s) to idle at a reasonable speed (under 1,000 RPMs).

Last year, I managed to come up with several DCNVH variants and they are interesting in that they were designed for plenum intake and have a power valve. Bonus is that there is no need to drill holes in throttle blades and the ones original to Maserati Bi-Turbo have correct choke tube and aux. venturi (booster) size for what I am doing. Emulsion tubes and jetting all need to be changed just as when setting up DCNF carbs for same engine, though.

The 36 DCNVHs used on naturally aspirated 1500cc and 1600cc Talbots and Sunbeams are hard to come by Stateside. The DCNVHs original to '84 - '85 Maserati Bi-Turbo (2.0 litre Euro spec and 2.5 litre US spec) are an ideal starting point for what I am doing but are scarce as well and crazy expensive if you can find them in good rebuildable condition, complete and unmolested. These are sealed in a pressurized box on the Bi-Turbo engine.

Best regards,

Harry
Why don't you guys just start another thread so this one isn't full of unneeded info?
JC -

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