Fine Tuning a 360 Magnum with a Brawler "Double Pumper"

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jmanhoff said:
Do I have this backward or the right idea?

Bigger main air bleed makes the boosters come in sooner but it’s richer down low, leaner up high.

Smaller main makes booster come in later and leaner, richer up high?
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YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES YES!

Now that you understand that you are on your way to being a carb tuner.

Where the booster starts is critical in getting everything timed up so you have enough overlap in circuits so you don’t have holes or dips in the fuel curve or equally as bad is too much overlap.
 
And remember the main air bleed is responsible for feeding all of the air available to the emulsion circuit. Hopefully you’re starting to see how one change can affect multiple different things. And small changes can quickly get out of hand, which is why it’s very important to know what you’re starting with.
 
jmanhoff said:
The current taps I have aren’t spiral tap but they are through taps so I guess I can start with those and see how it goes. I’m not going to be tapping a million holes anytime soon so I think I can suffice for now.

Here is a video of the exhaust, I would take a video of the carb side but it’s currently snowing and 25 degrees so it would take a year for the engine to warm up lol

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I can't imagine that all these holes go through into a larger passage? I would think you're going to need a bottoming tap to finish the hole. They aren't as common and if you can't find one easily, you can make one from a standard tap by grinding back the tip to the thread just before it goes to full diameter. You start the hole with the standard tap and when it bottoms out, switch to the bottoming tap to finish it. That allows the threads to go nearly to the bottom of a hole with a shoulder.
 
TT5.9mag said:
And remember the main air bleed is responsible for feeding all of the air available to the emulsion circuit. Hopefully you’re starting to see how one change can affect multiple different things. And small changes can quickly get out of hand, which is why it’s very important to know what you’re starting with.
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Yeah I’ve always understood that you should change as little things as possible with a carb but never understood the relationship between the circuits.

So in terms of the circuits, the idle and booster circuits are separate but they are hand in hand in a sense as they work together to get the thing moving.

Should I modify things one by one or should I put in the blanks for the emulsion, lower the IFRs and replace it with a .028, and have that as my starting point? I’d imagine I’d also want to square up the t slot as well
 
gzig5 said:
I can't imagine that all these holes go through into a larger passage? I would think you're going to need a bottoming tap to finish the hole. They aren't as common and if you can't find one easily, you can make one from a standard tap by grinding back the tip to the thread just before it goes to full diameter. You start the hole with the standard tap and when it bottoms out, switch to the bottoming tap to finish it. That allows the threads to go nearly to the bottom of a hole with a shoulder.
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That’s actually probably going to be something I end up doing. Bottoming taps aren’t readily available but I can order them, I think I mentioned that. I’ll have to see where these holes go to to see if I can get the tap all the way in. I think for the t slot restrictors if those are going into the main body then I wouldn’t need a bottoming tap, but the others it’s possible.

Do I want to have the emulsion blanks flush with the surface or sticking up a little is fine?
 
jmanhoff said:
Yeah I’ve always understood that you should change as little things as possible with a carb but never understood the relationship between the circuits.

So in terms of the circuits, the idle and booster circuits are separate but they are hand in hand in a sense as they work together to get the thing moving.

Should I modify things one by one or should I put in the blanks for the emulsion, lower the IFRs and replace it with a .028, and have that as my starting point? I’d imagine I’d also want to square up the t slot as well
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You already have a starting point. And we still don’t know what it is. Measure everything.
 
jmanhoff said:
That’s actually probably going to be something I end up doing. Bottoming taps aren’t readily available but I can order them, I think I mentioned that. I’ll have to see where these holes go to to see if I can get the tap all the way in. I think for the t slot restrictors if those are going into the main body then I wouldn’t need a bottoming tap, but the others it’s possible.

Do I want to have the emulsion blanks flush with the surface or sticking up a little is fine?
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When blocking emulsion just drill and tap deep enough for the set screw to sit flush. A little proud or a little deep is no big deal. But see post 332 above first.
 
jmanhoff said:
Yeah I’ve always understood that you should change as little things as possible with a carb but never understood the relationship between the circuits.

So in terms of the circuits, the idle and booster circuits are separate but they are hand in hand in a sense as they work together to get the thing moving.

Should I modify things one by one or should I put in the blanks for the emulsion, lower the IFRs and replace it with a .028, and have that as my starting point? I’d imagine I’d also want to square up the t slot as well
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Idle circuit
Main circuit

That’s all in a two circuit carburetor. You can call the transfer slots an intermediate circuit as that’s how they work. The boosters are on the main.
 
1739333682414.jpeg


So looking at this diagram I found on good old google, the idle circuit is the idle feed and the t-slot, so if I were to put in a smaller IFR it would lean out the idle and the t slot?

And would the air bleed also change the mixture to a point as well as the timing of the t slot?
 
jmanhoff said:
View attachment 1716365164

So looking at this diagram I found on good old google, the idle circuit is the idle feed and the t-slot, so if I were to put in a smaller IFR it would lean out the idle and the t slot?

And would the air bleed also change the mixture to a point as well as the timing of the t slot?
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The timing of the T slot is directly (and only) related to the throttle blade position. As you change the blade position with the curb idle screw, not only does idle speed change, but the AFR will change also because you’re exposing more or less of the slot. The idle air bleed has very little effect on T slot Fuel. The idle feed restricter will reduce the amount of fuel available to the idle mixture passage and the T slot but not in the capacity we’d all like it to. The Transfer slot will (sometimes) require its own restricter.
 
TT5.9mag said:
The timing of the T slot is directly (and only) related to the throttle blade position. As you change the blade position with the curb idle screw, not only does idle speed change, but the AFR will change also because you’re exposing more or less of the slot. The idle air bleed has very little effect on T slot Fuel. The idle feed restricter will reduce the amount of fuel available to the idle mixture passage and the T slot but not in the capacity we’d all like it to. The Transfer slot will (sometimes) require its own restricter.
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Okay so essentially, the idle air bleed and idle restrictor only directly control the idle circuit, and the transfer slot has “a mind of its own” in a sense even though it’s the same circuit as its related to the throttle position.

So ideally, I tap the main body to put in t slot restrictors and tune those along with the idle circuit to keep the t slot as square as possible?
 
The T slot being square is a starting point and can vary slightly. That’s ok. If you need more air but not fuel you can get bypass air from other sources (like pcv or secondary butterflies or some guys drill holes in the primary butterflies, I personally don’t see the need for that). But you don’t want to be too far off of square or slightly rectangular. The T slot kinda acts on its own and tuning the idle (air or fuel side) only has marginal effects on the T slot. Your carb on your engine may not need that level of tuning. Usually this type of tuning is reserved for racier, big cam, big carb stuff.
 
TT5.9mag said:
The T slot being square is a starting point and can vary slightly. That’s ok. If you need more air but not fuel you can get bypass air from other sources (like pcv or secondary butterflies or some guys drill holes in the primary butterflies, I personally don’t see the need for that). But you don’t want to be too far off of square or slightly rectangular. The T slot kinda acts on its own and tuning the idle (air or fuel side) only has marginal effects on the T slot. Your carb on your engine may not need that level of tuning. Usually this type of tuning is reserved for racier, big cam, big carb stuff.
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Yeah I figured, I think the only tricky tuning variable in this setup is how light the truck is, which makes the transitions difficult. A bunch of my parts are supposedly being delivered Friday though it’s USPS so it will probably be delivered next year.

I plan to put in a .028 IFR at the bottom of the well and block off the middle emulsion hole and start from there.

I also ordered a pin gauge which comes on Monday which I can use to measure the top bleeds to see if they are actually as big as they are stamped.
 
jmanhoff said:
Yeah I figured, I think the only tricky tuning variable in this setup is how light the truck is, which makes the transitions difficult. A bunch of my parts are supposedly being delivered Friday though it’s USPS so it will probably be delivered next year.

I plan to put in a .028 IFR at the bottom of the well and block off the middle emulsion hole and start from there.

I also ordered a pin gauge which comes on Monday which I can use to measure the top bleeds to see if they are actually as big as they are stamped.
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Yes, verify the sizing of everything.

There was a time there was a run of Holley jets that were manufactured wrong.

You could go up 10 jet sizes and go leaner. That’ll drive you nuts for a bit.

Ran into the same thing with nozzles and pulls for mechanical fuel injection.

There is nothing more aggravating that to install a bigger pill and have the engine go richer.

I had to pin every nozzle and pill every time I bought new ones.
 
Newbomb Turk said:
Yes, verify the sizing of everything.

There was a time there was a run of Holley jets that were manufactured wrong.

You could go up 10 jet sizes and go leaner. That’ll drive you nuts for a bit.

Ran into the same thing with nozzles and pulls for mechanical fuel injection.

There is nothing more aggravating that to install a bigger pill and have the engine go richer.

I had to pin every nozzle and pill every time I bought new ones.
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Well I guess it wouldn’t hurt to do it then lol. I have another question though, so most engines on average don’t really go into the boosters until about what, 3000ish? So does that mean if I was to run a smaller PMJ and a sooner opening PV it won’t really start feeding fuel until about that same rpm and it would be running off idle/t slot until then?

Basically I’m asking is the PV putting fuel into the same circuit as the jets when it opens so the timing for fuel delivery is the same, there’s just more?
 
jmanhoff said:
Well I guess it wouldn’t hurt to do it then lol. I have another question though, so most engines on average don’t really go into the boosters until about what, 3000ish? So does that mean if I was to run a smaller PMJ and a sooner opening PV it won’t really start feeding fuel until about that same rpm and it would be running off idle/t slot until then?

Basically I’m asking is the PV putting fuel into the same circuit as the jets when it opens so the timing for fuel delivery is the same, there’s just more?
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Exactly. The power valve should have been called the economizer valve because that’s really how it functions. Most of the time anyway.

The PV allows to run a much smaller primary main jet at a cruise and low loads.

When the load goes up (vacuum drops) and the PV opens and adds fuel.

When it opens is controlled by vacuum.

How much fuel it adds is controlled by the power valve channel restrictors, which is a fancy way of saying the power valve jets.
 
Newbomb Turk said:
Exactly. The power valve should have been called the economizer valve because that’s really how it functions. Most of the time anyway.

The PV allows to run a much smaller primary main jet at a cruise and low loads.

When the load goes up (vacuum drops) and the PV opens and adds fuel.

When it opens is controlled by vacuum.

How much fuel it adds is controlled by the power valve channel restrictors, which is a fancy way of saying the power valve jets.
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Okay, things seem like they’re starting to click. Obviously the power valve/jetting will probably be one of the last things I iron out but I’ve just been asking these questions as they pop into my head lol.

Would it be worth while to buy a PV block off for tuning the main jets/right PV or is that something you can really just “ear-ball” as I call it? I do hear the engine begin to sound labored around 15 inches while driving, and obviously I can hear the PV open under 9 inches, is that something that actually matters or is that purely just harmonics of the engine
 
jmanhoff said:
Okay, things seem like they’re starting to click. Obviously the power valve/jetting will probably be one of the last things I iron out but I’ve just been asking these questions as they pop into my head lol.

Would it be worth while to buy a PV block off for tuning the main jets/right PV or is that something you can really just “ear-ball” as I call it? I do hear the engine begin to sound labored around 15 inches while driving, and obviously I can hear the PV open under 9 inches, is that something that actually matters or is that purely just harmonics of the engine
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I block the PV when I start tuning unless it’s on the dyno. Then I wing it.

Don’t lose sight of main air bleed size and when the boosters start.

Most of the carbs like you have I’ve done have a .033 main air bleed and that’s pretty big.
 
Newbomb Turk said:
I block the PV when I start tuning unless it’s on the dyno. Then I wing it.

Don’t lose sight of main air bleed size and when the boosters start.

Most of the carbs like you have I’ve done have a .033 main air bleed and that’s pretty big.
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Should I go down to a .028 like you mentioned a bit ago in the thread?
 
jmanhoff said:
Should I go down to a .028 like you mentioned a bit ago in the thread?
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Measure it first and then we can figure it out.

I have the benefit of doing enough of these carbs that I have pretty much developed tune ups that I start with.

Surprisingly most of it is pretty much what Holley sent the carbs out with back in the day.

Two emulsion holes. I now just do T slot restricters. I almost always take some fuel out of the idle feed restriction because Holley sent them out pretty fat at idle.

The other thing I started doing but I tell most guys to leave it alone because you change the tune up enough that the final tune up is unorthodox for lack of a better term. That is I remove the plugs in the main well and I drill it out to .185ish.

You can go down all kinds of rabbit holes with some of this stuff.
 
Newbomb Turk said:
Measure it first and then we can figure it out.

I have the benefit of doing enough of these carbs that I have pretty much developed tune ups that I start with.

Surprisingly most of it is pretty much what Holley sent the carbs out with back in the day.

Two emulsion holes. I now just do T slot restricters. I almost always take some fuel out of the idle feed restriction because Holley sent them out pretty fat at idle.

The other thing I started doing but I tell most guys to leave it alone because you change the tune up enough that the final tune up is unorthodox for lack of a better term. That is I remove the plugs in the main well and I drill it out to .185ish.

You can go down all kinds of rabbit holes with some of this stuff.
Click to expand...

Would the reason I don’t get highest vacuum until the idle screws are basically entirely in be because of how fat they come out the box now?
 
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