Motorsports Village

Tuning A Holley Dominator Transfer Slot
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Author:  oobob [ Fri Feb 15, 2008 3:43 pm ]
Post subject:  Tuning A Holley Dominator Transfer Slot

Ken, you made a comment about the transfer slots themselves, what do i need too know??? #-o  :-k

Author:  Ken0069 [ Fri Feb 15, 2008 6:29 pm ]
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You should see a tiny bit (.020 or so) of the T slot below the butterflies in their normal idle position.  If not, then you will have to lengthen them a little to get there.  If the slots are very close but just short by .010 or so, you can file the bottom edge of the throttle blades on a 45* angle to get the correct exposure without having to lengthen the slots. Here's a picture of how I did them on an 1150 Dominator that the slots were short on.


Quality Control on the newer carbs isn't as good as it was on the old ones as I didn't have to do anything to the ones on my old style 8896.  If you need to lengthen yours then you can take a small file and grind the flat sides smooth to fit into that groove then use the edge to file that slot longer.  Let's hope yours isn't horked up either so you won't have to!   ;-)

EDIT: This post was edited on 11/6/2011 to note that the T slot should be checked AFTER the engine is started and the carb is set to it's normal idle RPM with BOTH the primary and secondary open approximately the same amount. After that you pull the carb back off and look to see how much T slot is visible below the throttle blades. If you have NONE showing, take a scribe and scribe a line where those blades are at normal idle, then you can run the blade shut to see how much you need to lengthen them or how much to file the throttle blade. Adjust as needed at this time.

EDIT: This post was edited again on 11/13/2012 to add the part about filing the 45* angle on the edge of the throttle blades in the area adjacent to the T slots. I like doing this if possible to avoid lengthening the T slots as if you're not happy with all this and want to go back to where you were before you started, then a set of throttle blades are cheaper than another main body. Also, on a different engine the T slot exposure may be OK. I just hate lengthening that slot unless it's absolutely necessary and filing the blades is a better choice if possible!

Author:  Scott Smith [ Fri Feb 15, 2008 8:14 pm ]
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Wish mine were like that. Mine are the other way. They have about .050 showing with the blades closed completely. Speed screws backed all the way out!  O:)  O:)

Author:  oobob [ Fri Feb 15, 2008 8:57 pm ]
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No slot visible with the blades closed =P~
A picture of that file would be nice.
Seams to have a very slight hesitation when going up on the converter but, my linkage is 1 to 1 also, i'll probably need to keep it this way in case a little .90 racing comes along. :-#

Author:  Ken0069 [ Fri Feb 15, 2008 9:40 pm ]
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Do you have the pump shot adjusted correctly?  You want the diaphram to be within about .015 or so from bottoming out at WFO. You can bend the pump arm on the cam some by putting a little more kink at the end to make sure you have full stroke on it.

Some guys make those T slot cutters out of hack saw blades ground down to fit in that slot.  I'd say the saw blade would be the easiest to do.  Just make sure you use a fine tooth blade to start with.

You'll probably have to use your imagination on the slot cutter as I've never done one so I have no idea what's involved.  I do have some ideas though.

If using a hacksaw blade I'd start with a new one.  First I'd grind the end flat across where it has the radius.  Then grind both sides down about one inch from the end until it would fit into that slot with just a small amount of clearance.  Once this is done grind off the back side and leave it about 1/4 inch wide.  Make sure to deburr the rough edges where you cut it down to size but not the the teeth as they need to cut the slot.  

You'll probably have to cut it kinda short to be able to get into that opening.  A small pair of vice grips could help hold it or you could make a small handle with slot and a set screw to do that also.

Hand work the slots or file the throttle blades until you have the right amount exposure showing below the closed butterfly in it's normal idle position.

Author:  oobob [ Sat Feb 16, 2008 5:19 am ]
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Do the slots have to be at a 90* angle to the venturi or is it ok to be at about a 30* angle? If 90* is required, wouldn't you have to remove the throttle shafts in order to make them square?  #-o  :-k

Thanks, Guy's

Author:  Scott Smith [ Sat Feb 16, 2008 10:37 am ]
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This is mine with the blades 100% closed. So you can imagine how much is exposed when the speed screws are set.


Author:  Tuner [ Sun Feb 17, 2008 1:56 am ]
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The little files I use are longer than the diameter of the throttle bore so that’s how much angle I end up with, doesn’t seem to make much never-mind.

The T-slot location is a matter of getting enough slot exposed to the metering pressure (vacuum) below the butterfly to cause fuel to feed from the slot at idle so the slot isn’t dry when the throttle is initially opened above the curb idle.  The general concept (or one way of looking at it) is - If the tune were perfect, the amount of exposed T- Slot at the desired idle speed would supply the ideal AFR and no adjustable mixture screw would be needed.  The reality is circumstances are always changing (temp-altitude-etc.) and the minor imperfections of the small orifices cause enough deviation at such small flows that the ability to trim the curb idle mixture is necessary.  

The occasional carb with the unfortunate circumstance like Scott’s, more of the slot exposed than is ideal or desired, can still be tuned unless it’s ridiculously extreme.  It does require more effort in the low speed circuit tuning and will end up with much less Curb Idle mixture screw open because of the substantial amount of fuel delivery from the exposed slot.  Either way it’s more time, if the slot isn’t exposed at all you have to do the precision hand work and if it’s exposed too much it takes a little more tinkering with the tuning.

I had the too much exposure situation last summer with 2 1050’s on an 8-71 blown 540BBC in a pleasure boat that had to idle like a stocker for water skiing and getting in and out of the marina.  Fortunately, there was some dyno time before the engine went in the boat but it probably took 2 hrs of fiddling just the idle circuit to get it to behave, an hour on the dyno and an hour in the water.  Had to put up with the railbirds, “I can’t believe he’s using the dyno to tune the idle, etc….”  I was using the dyno to tune the off-idle and up the T-slot and they just couldn’t grasp the concept of using a dyno for less than “making pulls”.

Author:  oobob [ Wed Feb 20, 2008 12:56 pm ]
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Got the slots cut, started engine and ran about 15 minutes and discovered water & oil still don't mix [-(  can you say cracked head =P~  so after 2-1/2 days $300 in welding & machine work i'm almost ready to try again :-#

Author:  Slowpoke [ Wed Feb 20, 2008 6:45 pm ]
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A pessimist would probably say "Damn carburetor!"

An Optimist would say "Glad that didn't happen in competition"

I think race cars are like boats, they don't normally break at home. As always, it could've been worse, all things considered.

Hope your carb tuning goes good, I haven't had a chance to play with my T-slots yet, I think I lucked out and they were pretty close.


Author:  oobob [ Wed Feb 20, 2008 7:24 pm ]
Post subject: 

I made a t-slot tool from a standard 24 tooth per. inch hacksaw blade, the slots are .025 wide so you will have to grind the sides of the blade, also notice which direction the teeth are.

In order not to get the slots too long, i closed the throttle blades and used a small pick  to make a scribe mark even with the bottom of the blades and then sawed the slots about .010 past the scribe mark. If it needs more slot they're easy to cut.

Author:  Brktracer [ Wed Feb 25, 2009 11:22 pm ]
Post subject:  Re: Tuning a converted dominator T-slot

Mark, I hope you saved that tool! I might need to borrow it.

I got my carb back yesterday and did some testing today. It's much better. I haven't driven the car yet but AFR revving the engine looks much better.

It has a slight hesitation off idle. The T slots might be too short. I don't think any is exposed at idle.

Weather's not looking good!

Author:  oobob [ Thu Feb 26, 2009 7:28 am ]
Post subject:  Re: Tuning a converted dominator T-slot

Tool is rite here, for the off idle hesitation I would try a larger squirter, back idle mixture screws out a tad or a tad smaller IAB.
If the slots aren't exposed a little, they may be dry when ideling and take a split second to start flowing fuel.
Weather doesn't look good at all.

Author:  Ken0069 [ Thu Feb 26, 2009 9:32 am ]
Post subject:  Re: Tuning a converted dominator T-slot

You might have already checked this but on my 1050 I had to bend the cam end of the pump lever in a slight curve to make it open the pump all the way. (yellow cam) At WFO I'm at full travel on the pump. Also make sure you don't have too much clearence between the actuator bolt with the spring and the pump lever.

Have you looked at the position of the T slots after you've actually had that carb idling on the engine? All 4 throttle plates should have a small amount of T slot showing just below the edge and if memory serves, around .020 or so is "normal" if there is such a thing.

And as Mark mentioned, sometimes just a little more idle fuel will help with this. What is your idle AFR now?

Author:  Brktracer [ Thu Feb 26, 2009 11:50 am ]
Post subject:  Re: Tuning a converted dominator T-slot

I haven't looked at the slots since putting the carb back on. Currrently I have the idle AFR at 14.3.

Getting this tip in right is just being picky. I just want it to feel and sound clean. It's really not bad.

I pulled everything apart before I started and made a bunch of notes so I can get back to baseline if I ever need to. A whole page of notes!

Before cutting, maybe I can set the primarys with about .030 of the slot showing and set the idle speed with the secondaries and see how it does. I'll only cut as a last resort!

No doubt it's better. The boosters actually atomize the fuel now! \:D/

One thing I haven't done is put in a new set of plugs. I need to do that before changing anything else. I bet those suckers are black! That and an oil change!

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