Holley Transition Circuit Tuning

[mopowers]

I'm in the middle of tuning a Brawler 750 on my 340. It runs fat everywhere, so I drilled and tapped the idle feed restrictors, PV channel restrictors and transfer slot restrictors.

After looking at the transfer slot itself, a question came to my mind. The slot measures as .025" x .190" for a total area of .0048 sq. in - which is equivalent to a .078" (or 5/64") drill bit. Does that mean that unless you go smaller than .078" for a restrictor it wouldn't end up "restricting" anything since the slot itself would act as the restriction???

For what it's worth, the original size of the transfer slot port was .115", so I would think the slot would be the restriction in that configuration (port is .01 sq in vs .0048 for the slot). Is that true?

 

[abodyjoe]

 

[Newbomb Turk]

I'm in the middle of tuning a Brawler 750 on my 340. It runs fat everywhere, so I drilled and tapped the idle feed restrictors, PV channel restrictors and transfer slot restrictors.

After looking at the transfer slot itself, a question came to my mind. The slot measures as .025" x .190" for a total area of .0048 sq. in - which is equivalent to a .078" (or 5/64") drill bit. Does that mean that unless you go smaller than .078" for a restrictor it wouldn't end up "restricting" anything since the slot itself would act as the restriction???

For what it's worth, the original size of the transfer slot port was .115", so I would think the slot would be the restriction in that configuration (port is .01 sq in vs .0048 for the slot). Is that true?

Start at .068 and tune from there.

Also, you should drill and tap the emulsion ports in the metering block. If it has four emulsion jets use the top and third from the top. No bigger than .028 and probably .026 is a bit cleaner.

I’ve never seen an engine want four (or five, I’ve seen that before) emulsion holes open. It will cause slugging, where you get a slug of fuel and then a slug of air.

It can drive an O2 sensor wild. And it’s a PITA to tune around, if can.

 

[mopowers]

Thanks. I saw that last night. Coincidentally, that's the same Brawler carb I'm working on. The video itself isn't too helpful though. Seems like he never did get it running right.

Start at .068 and tune from there.

Thanks. I'll go with .068" for the transfer slot restrictor then. Is my assumption correct though - that anything above a .078" and the slot itself becomes the restriction?

Also, you should drill and tap the emulsion ports in the metering block. If it has four emulsion jets use the top and third from the top. No bigger than .028 and probably .026 is a bit cleaner.

I’ve never seen an engine want four (or five, I’ve seen that before) emulsion holes open. It will cause slugging, where you get a slug of fuel and then a slug of air.

It can drive an O2 sensor wild. And it’s a PITA to tune around, if can.

It has 3 emulsion ports - with only the top and bottom drilled through. They're sized at 0.028"

What PV channel restrictor size would you start with? They seemed quite large out of the box. They were like .076" if I recall.

 

[TT5.9mag]

Thanks. I saw that last night. Coincidentally, that's the same Brawler carb I'm working on. The video itself isn't too helpful though. Seems like he never did get it running right.


Thanks. I'll go with .068" for the transfer slot restrictor then. Is my assumption correct though - that anything above a .078" and the slot itself becomes the restriction?



It has 3 emulsion ports - with only the top and bottom drilled through. They're sized at 0.028"

View attachment 1716460247

What PV channel restrictor size would you start with? They seemed quite large out of the box. They were like .076" if I recall.

The stock Holley TS opening in my blocks was .110, I started tuning at .081 and ended up at .066 (going off memory). Your assumption is correct that the area of the t-slot opening itself is the restriction to begin with and only when you use a “jet” with less area will you be restricting fuel flow.
For PVCR size, you’ll have to do some math for a starting point. Take the area of the main jet (X 2), and the area of the PCVR (X 2) and compare it to the area of the secondary jet (X 2). (Assuming the secondary isn’t running a pv.) keep that relationship pretty close amd you’ll be poopin in tall cotton.

 

[TT5.9mag]

A better way to say the same thing is

Total area of 70 main jets plus PVCR is equal to that of 80 secondary jets. Thats kinda a good place to start tuning. It keeps fuel flow across the engine pretty consistent.

 

[mopowers]

For PVCR size, you’ll have to do some math for a starting point. Take the area of the main jet (X 2), and the area of the PCVR (X 2) and compare it to the area of the secondary jet (X 2). (Assuming the secondary isn’t running a pv.) keep that relationship pretty close amd you’ll be poopin in tall cotton.

Thank you! That makes a ton of sense. You're correct - no secondary PV.

The original jet sizes were 72 (primary) and 80 (secondary). I bumped them down to 68s and 76s. After doing the math:

0.0055418 sq in (76 jet: 0.084") - .0037393 sq in (68 jet: 0.069") = 0.0018025 sq in (which corresponds to a 0.048" diameter hole)

I guess .048" is where I'll start. Thank you again!

 

[Newbomb Turk]

You PVCR size will change with your MAB size. If it were me, I’d use a .026 MAB and a .062 PVCR and tune from that.

That metering block looks like the upper emulsion hole is below float level. And the stack is very close together. Hmmmm.

Also, I can’t see where the IFR is, bit if it’s in the top you should move it to the bottom while you’re in there.

.028 IFR and .072 IAB is a safe start and if it’s a bit lean you can drop the IAB to .067-.068 and fatten it up if you need to.

 

[mopowers]

You PVCR size will change with your MAB size. If it were me, I’d use a .026 MAB and a .062 PVCR and tune from that.

That metering block looks like the upper emulsion hole is below float level. And the stack is very close together. Hmmmm.

Also, I can’t see where the IFR is, bit if it’s in the top you should move it to the bottom while you’re in there.

.028 IFR and .072 IAB is a safe start and if it’s a bit lean you can drop the IAB to .067-.068 and fatten it up if you need to.

Thank you again. I appreciate the input

Yes, the IFRs are in the bottom location. All I did was drill out the brass plugs and tapped them for 6-32 set screws. The IFRs out of the box were .027, which are pretty small. I'm going to stick with those for now. The IABs are .070", so pretty close to what you called out.

 

[crackedback]

@mopowers

You have that spreadsheet I did up?

 

[mopowers]

@mopowers

You have that spreadsheet I did up?

I did at one point. I looked for it earlier today though and couldn't find it on my computer. I'm thinking it got lost when I got another computer a few yrs ago. Just shot you a PM.

 

[RustyRatRod]

That must be an older "Brawler". All of them I've seen already have "all that" adjustable.

 

[Mattax]

.025 x .190 seems like a decent starting point. I wouldn't use a TSR unless you can't get it to go cleanly from idle to off-idle and onto the mains. Work on the initial opening, IFR, and IAB first.
The transfer slot is a both an air bleed and a restriction. Restricting the fuel in is trimming of fuel that already has a air introduced into it. Its one way to deal with slots that are too long and certain idle low rpm engine characteristics.

racingfuelsystems-Making throttle slots smaller?

racingfuelsystems

www.tapatalk.com

racingfuelsystems-Transfer slot lengths

Is there a list that states what the correct length of transfer slots should be for various popular Holley carbs? Like a 600 VS & 750 VS as well a

www.tapatalk.com

 

[mopowers]

That must be an older "Brawler". All of them I've seen already have "all that" adjustable.

It's about a year old. Funny enough, the instructions that come with all brawler carbs mention adjustable air bleeds, PVCRs, and IFRs (see below).

When I called Holley and asked them, I was told only the race brawlers come with adjustable IFRs and PVCRs, where as the street carbs like the one I have do not - not even on new ones. At the end of the day, I don't really care. I got a great deal on it and don't mind the extra work.

 

[mopowers]

.025 x .190 seems like a decent starting point. I wouldn't use a TSR unless you can't get it to go cleanly from idle to off-idle and onto the mains. Work on the initial opening, IFR, and IAB first.
The transfer slot is a both an air bleed and a restriction. Restricting the fuel in is trimming of fuel that already has a air introduced into it. Its one way to deal with slots that are too long and certain idle low rpm engine characteristics.

http://[URL]https://www.tapatalk.co...tems/making-throttle-slots-smaller-t1600.html

[/URL]

http://[URL]https://www.tapatalk.com/groups/racingfuelsystems/transfer-slot-lengths-t1285.html

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Thank you. This is great information. I was having difficulty getting a clean transition into the mains. It went rich right off idle.

 

[RustyRatRod]

It's about a year old. Funny enough, the instructions that come with all brawler carbs mention adjustable air bleeds, PVCRs, and IFRs (see below).

View attachment 1716460460

When I called Holley and asked them, I was told only the race brawlers come with adjustable IFRs and PVCRs, where as the street carbs like the one I have do not - not even on new ones. At the end of the day, I don't really care. I got a great deal on it and don't mind the extra work.

That's really interesting, because I have the Slayer VS carburetor on Vixen and it had adjustable everything, like those instructions say. I also had a brawler 650 DP that had everything adjustable. Strange indeed.

 

[mopowers]

That's really interesting, because I have the Slayer VS carburetor on Vixen and it had adjustable everything, like those instructions say. I also had a brawler 650 DP that had everything adjustable. Strange indeed.

Hmm... Maybe they did at some point. Oh well. No biggie.

 

[RustyRatRod]

Hmm... Maybe they did at some point. Oh well. No biggie.

Yeah I know then did. I had one. This is strange. Which one did you get, exactly?

 

[mopowers]

Just went on a test run. The jump down to 68s on the transfer slot restrictors was too much. It went lean right off idle this time - not horrible though. I'm going to try 76s next. If it needs much more than that, I'll have to tap them at 10-32 and pick up some 10-32 set screws since hex on the 8-32 screw limits the hole size to .078.

Also - the idle mixture screws are at 7/8 turn out to get most vacuum, which puts the AFR at low-mid 13's at idle in gear. I'm wondering if smaller IRFs would help get more adjust ability out of the mixture screws or if it's even needed.

 

[mopowers]

Yeah I know then did. I had one. This is strange. Which one did you get, exactly?

https://www.holley.com/products/fuel_systems/carburetors/street/parts/BR-67213

 

[TT5.9mag]

I'm wondering if smaller IRFs would help get more adjust ability out of the mixture screws

Idle air bleeds will.

 

[mopowers]

Idle air bleeds will.

So in my case, would I go smaller or larger on the idle air bleeds?

 

[TT5.9mag]

Just went on a test run. The jump down to 68s on the transfer slot restrictors was too much. It went lean right off idle this time - not horrible though. I'm going to try 76s next. If it needs much more than that, I'll have to tap them at 10-32 and pick up some 10-32 set screws since hex on the 8-32 screw limits the hole size to .078.

Good. It’s nice when you make changes and the engine responds to them. Even if the result isnt what you were after. At this point you have a “window” that you know you need to stay within.

 

[RustyRatRod]

I think you got something weird. Even the carburetor picture in that ad shows replaceable air bleeds.

 

[TT5.9mag]

So in my case, would I go smaller or larger on the idle air bleeds?

Larger. More air at the bleed will require you to open the mixture screws for more fuel.