That's why I always tune my auto transmission cars in gear, the initial timing, idle speed and idle mixture is best set that way.
Don't need to use no stinking full vacuum. can you smell it. lol
Fine Tuning a 360 Magnum with a Brawler "Double Pumper"
- Thread starter jmanhoff
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Don't need to use no stinking full vacuum. can you smell it. lol
Damn fish
Active Member
What carb do you use ? I have a Brawler on my car and don't know why people keep talking main air bleed when there's a low speed air bleed
I've used both. Right now, I'm using a 450 VS Slayer on my slant 6 and it runs fantastic. I have a 650 Brawler DP I've used on both the slant 6 and the 400 Ford engine in my 75 F250. On both the Quick fuel carburetors, my experience has been that the bleeds on top of these carburetors are much more for fine tuning and the fuel restrictors in the metering blocks are more for making larger adjustments.I get the fuel restrictors close first and then fine tune with the air bleeds. I took the 650 off the slant 6, because, while it ran great and produced more power than the 450, it was difficult to get the low speed mixture correct. I knew the 450 was a dead match, so I put it back on. I took it off the Ford, because amazingly, it wasn't enough for it and I have a Street Demon 750 three barrel on it now and it runs great.
Newbomb Turk
Well-Known Member
Because the main air bleed controls when the booster starts.
Get it too big and the booster starts too soon. So you are pulling fuel from the booster, and from the T slots and depending on emulsion and idle air bleed/idle feed restriction you still are pulling fuel from the idle circuit.
You can’t unfuck that with an idle air bleed change.
Thats why I keep saying all these carbs coming with an assload of emulsion (because somehow in the 1990’s when all this bullshit started it became “orthodoxy” that emulsion was to add air to the system and that’s not what it’s for) and big main air bleeds (I won’t even get into transfer slot length and width) are straight garbage and need to be fixed.
You ain’t fixing all that with an idle air bleed change.
That’s why it keeps getting brought up.
Damn fish
Active Member
Ok thank you. I didn't have a high vacuum situation but 11 inches at idle and when I tried to gently get moving it would lean misfire and die. I dropped two low speed bleed sizes and problem solved. 70 to 68
My slant 6 has 6 hg at idle.
Damn fish
Active Member
Wow do you drive it on the street or only strip
It's an everyday driver when the weather is good. She has a leak at the passenger door seal so I don't drive her in the rain.
And lots of reversion
If you say so.
Okay for some reason I stopped getting emails for this thread but I figured I’d come back in. For starters, are there any off the shelf timing lights that you can get today that are actually accurate? I have a harbor freight dial back and I don’t trust it completely especially after watching some videos, especially from Uncle Tonys Garage.
I bumped up the accelerator pump nozzles from 31s to 35s, couldn’t find any 33s easily. I also, yes against what people said in the forum, bumped up to a 9.5PV (I didn’t notice a drop in mpg), but this combo did make it more driveable by a good amount. I do have a slight stumble still though off idle or when I goose it. Best I can describe it is like an old cash register going “cha-Ching”. That’s the rate that it bogs then goes.
I bumped up the accelerator pump nozzles from 31s to 35s, couldn’t find any 33s easily. I also, yes against what people said in the forum, bumped up to a 9.5PV (I didn’t notice a drop in mpg), but this combo did make it more driveable by a good amount. I do have a slight stumble still though off idle or when I goose it. Best I can describe it is like an old cash register going “cha-Ching”. That’s the rate that it bogs then goes.
Newbomb Turk
Well-Known Member
Just use the timing light you have and use whatever numbers the engine wants.
If it runs the best at 20 total or 40 total as long as you use the same light every time they didn’t matter.
Now that you have the power valve fairly sorted out, it’s time to look at your emulsion stack.
If you have 3 emulsion holes you block the middle hole and no bigger than .028 holes in the other two. .026 is better and .024 may be the best but you really need to test for it.
If you have 4 emulsion blocks the 1 and 3 need .028 holes and 2 and 4 get blocked.
If they are 5 emulsion blocks you can block 1,3 and 4 and .028 in the other two.
.026 is probably better.
You can get too much emulsion and it will “slug” fuel. You can see it with an O2 sensor.
You will see a saw tooth pattern for your AFR.
Most carbs have too much emulsion. They are not there to add air to the fuel, they are to correct the fuel curve.
Alright I’ll start researching those. I do still need to turn the carb around as many have pointed out, I have the cable just need to get some fuel line because the Brawler doesn’t seem to have a reversible inlet.
Okay gents so small update, I played with the timing (not the curve yet), and basically just did power timing. Seems happy around 13 degrees initial, any more and I get pinging but this could probably be fixed if I retard the mechanical advance. I did also adjust the accelerator pump according to the way Holley says to. WOT should be able to fit a .015 feeler between the arm and the screw. I still have a very slight stumble though... still has that "cha-ching" rev. Is it possible I'd need to go up another pump nozzle size?
Newbomb Turk
Well-Known Member
There should be .000 clearance at wide open on the accelerator pump.
I have no F’ing idea how Holley came up with that one either.
You can add pump nozzle to it, but I’d keep digging to find out why it wants a big pump shot.
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Holley had the same person do that pump arm setting that came up with power valve rating 1/2 of idle vacuum.
If you change the pump cam, make sure it isn't bottom out the diaphram, binding the arm, etc. readjust it after the change.
Should I try to change the slot the cam is set on? I think in the video I watched Holley said setting 1 is generally for engines idling below 1000rpm and 2 is for over 1000rpm. I have my idle set right now at about 750-800, any higher and I start getting dieseling issues. When it had the stock jets in it it didn't stumble the way it does now but chasing better mpg I'm running the smaller jets and trying to work around it.
I know many people say that jets don't affect mpg because when I'm cruising down the highway I'm on the idle circuit but I have to say this: if jets don't change economy when cruising and I needed to fix my mixture setting instead, why did leaning out the idle mixture get me from 6mpg highway to 7mpg highway but changing jets from a 71 primary to a 66 primary (not right away, over time) get me from 7mpg to as high as 16mpg?
JMO, you have an initial timing issue (lack of - requiring blades to be open too much) if it is dieseling.
Or a potential vacuum leak somewhere. Small cam shouldn't need a bunch of timing maybe 14-16 max. Roller cam maybe a bit more, my 340 with a 214/224 liked 18-20 so...
Give it what it wants and get the idle tune squared away, EVERYTHING builds off that foundation.
Or a potential vacuum leak somewhere. Small cam shouldn't need a bunch of timing maybe 14-16 max. Roller cam maybe a bit more, my 340 with a 214/224 liked 18-20 so...
Give it what it wants and get the idle tune squared away, EVERYTHING builds off that foundation.
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You don't retard the mechanical advance. You limit it. In other words you stop it from advancing "as far".
Newbomb Turk
Well-Known Member
You do cruise on the main jet. If you are cruising on the idle circuit something is wrong.
The correct procedure to tune for primary main jet size is to block the power valve off.
Then drive the car on a flat road at cruise speed. Keep reducing the primary main jet until you get a SLIGHT lean surge.
Go up two sizes and never touch the primary main jet again, unless you are tuning for cruise.
Reinstall the power valve.
To tune for wide open throttle you increase the size of the power valve channel restrictors to add fuel at WOT on the primary side.
Of course if it’s too fat at WOT you reduce the size of the power valve channel restrictors.
And the main jet on the secondary side for WOT.
You never want to change the primary main jet to correct for WOT. Ever. This comes from a misunderstanding of how the power valve and main jet systems work together.
You cruise on the primary main jet. So you want that as lean as the engine will tolerate. Then the power valve adds fuel at WOT and at tip in.
Also, keep in mind that the main air bleed controls when the booster starts to add fuel. I harp on this constantly because it’s misunderstood and getting it wrong is one of many tuner induced holleyitis that is all too common.
A bigger main air bleed will start the booster sooner, so the engine will be richer, sooner. If you start the booster too soon, the engine has more fuel than it needs so we start reducing the primary main jet when in reality that big(ger) main air bleed is making it rich.
Also the bigger main air bleed will make the engine leaner at high rpm (air flow).
A smaller main air bleed will delay the start of the booster, so you will be on the T slot longer before the booster starts adding fuel. It will also be richer at high rpm (air flow).
You can get lost very quickly if you aren’t careful.
And to make things worse, we are still living in the dark days of the 1990’s when emulsion became the playground of carb tuner wannabes.
Too much emulsion will cause too in issues that get blamed on everything but too much emulsion.
To that end, I have a base tuneup that I start with. I use an .026 main air bleed and two .028 emulsion jets.
If you have annular boosters you will most likely end up with just one emulsion hole. If you have tunnel ram and annular boosters I pretty much guarantee you’ll only need one emulsion jet. You just block the rest.
Edit: I forgot to mention this all assumes you have the timing correct.
Yeah still have a couple things to tune out and figure out, first time ever messing with a carburetor. I do currently have the timing set at 13 degrees initial which I came to after advancing it until it pinged then backed off a couple. Vacuum advance is on manifold vacuum so it helps bring up my idle rpm so I can keep the throttle closed more (helps with dieseling). I have the idle mixtures as lean as the engine is happy and with the highest vacuum, backed off ever so slightly rich.
I was kind of confused about the whole you cruise on your idle circuit claim so I took it with a grain of salt and changed the jets anyway. I ended up sticking with a 66 primary as when I went to a 64 it was sluggish and at part throttle (cruising) it would very slightly buck and surge and if I gave it a kick without opening the secondaries it would backfire out the carb, so I went back to the 66s and they’ve been in for about a month now. Still haven’t really played with the secondary jets though other than switching them from a 74 (stock) to a 71 (stock primary jet).
I still need to flip the carb around, I’m yet to mess with the weights and springs in the distributor but I still need to do that. When I said retard the mechanical advance I meant hold it for longer so it comes in later which I’m sure is something I can mess with with a spring kit I have.
I’m planning to get a new exhaust done up in the next couple of weeks so I feel like before I start messing with the internals of the carb I should have everything setup how it’s going to be before I start tuning it. (Correct me if I’m wrong.)
I’m getting a whole new exhaust from the headers back. 2.5 inch duals all the way back, H pipe followed by magnaflow 4 inch round straight through mufflers and following the stock exhaust routing so both pipes exit out the passenger side. I’m sure it will flow a lot more than the stock y-pipe setup it has currently. I do also plan to get an open element filter, one of those eBay 14x3 filters with the chrome housings. I know it’s really not a big change but it seems like carburetors really prove the “an engine is nothing but an air pump” saying so with all of this free flowing air I’m enabling I think it would have at least some affect.
I was kind of confused about the whole you cruise on your idle circuit claim so I took it with a grain of salt and changed the jets anyway. I ended up sticking with a 66 primary as when I went to a 64 it was sluggish and at part throttle (cruising) it would very slightly buck and surge and if I gave it a kick without opening the secondaries it would backfire out the carb, so I went back to the 66s and they’ve been in for about a month now. Still haven’t really played with the secondary jets though other than switching them from a 74 (stock) to a 71 (stock primary jet).
I still need to flip the carb around, I’m yet to mess with the weights and springs in the distributor but I still need to do that. When I said retard the mechanical advance I meant hold it for longer so it comes in later which I’m sure is something I can mess with with a spring kit I have.
I’m planning to get a new exhaust done up in the next couple of weeks so I feel like before I start messing with the internals of the carb I should have everything setup how it’s going to be before I start tuning it. (Correct me if I’m wrong.)
I’m getting a whole new exhaust from the headers back. 2.5 inch duals all the way back, H pipe followed by magnaflow 4 inch round straight through mufflers and following the stock exhaust routing so both pipes exit out the passenger side. I’m sure it will flow a lot more than the stock y-pipe setup it has currently. I do also plan to get an open element filter, one of those eBay 14x3 filters with the chrome housings. I know it’s really not a big change but it seems like carburetors really prove the “an engine is nothing but an air pump” saying so with all of this free flowing air I’m enabling I think it would have at least some affect.
Is there a particular wide band tuner you recommend? Or do you even use them? Keep in mind 2 things. I'm on a tight budget and I only need one O2 sensor. lol
I also will ask this lol. I’m getting o2 bungs welded into my new exhaust but am only going to run 1 for now probably.
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