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

[jmanhoff]

Hi all,

First time posting on the forum, I was posting on DodgeForum but was pointed here by another member as the first gen Dakotas are mainly EFI, and this forum has more knowledge on carbs. I've been chasing a couple of issues but wanted to get some final input to help me fine tune my carb.

For starters, I have a 1992 Dakota with a 5.9 out of a 1999 1500 mated to the stock 5 speed. Edelbrock Performer RPM Air-Gap, Brawler BR-67276 Street Avenger Mechanical Secondary 650CFM carb, Comp 20-745-9 cam considered a "towing cam" for the 5.9, JBA shorties, and then just the stock y pipe into a flowmaster super 44.

Timing is about 14 degrees, and I currently have #66 primaries, I swapped the secondaries to #71s but I'm not really worried about the secondary circuit right now as I really don't get into it too much. Stock had a #71 primary and a #74 secondary. Still have the stock 6.5 PV and stock accelerator pump nozzle. My current list of issues are as follows:

- Cold starts are extremely rich and it backfires during high idle (I can hear faint popping from the tailpipe, this is a new issue.)
- I have to let the truck warm up for at least 10 minutes before I can actually drive, and I don't mean comfortably I mean it will not drive if I put my foot down at all it will stumble, backfire, or die.
- It has a sometimes really bad off-idle stumble, sometimes it just will fall on its face, sometimes it will backfire through the carb.
- It smells rich and tailpipe is black after cruising.
- I'm trying to break the 10mpg city driving line, this is a "daily", not a race truck lol.

I currently have a size 35 pump nozzle (bigger) and a 9.5 PV on order to experiment with, as well as #64 jets currently on hand. I did put the 64s in but I felt what I would guess is lean surging while cruising at moderate throttle in a high gear at low rpm, which is part of the reason I ordered a 9.5 PV.

This engine is very vacuum happy, at least from what I've read about other SBMs. A little over 20 inches at idle, cruise is about 16-18. I know there is a lot of controversy about how you should pick your PV size but I feel like 9.5 is a good size for my setup because while experimenting with vacuum, I rarely if ever dipped under 7 inches under normal driving conditions. Right around 9 is where I can hear the engine kind of surging and if I give it a bit more throttle but don't open the secondaries it really starts to choke. That's the thing that got me thinking I should buy a 9.5 PV.

Of course the best way to tune the jets is with an AFR gauge but until I install one I've been reading the plugs and I guess smelling the exhaust but thats not exactly accurate lol. The plugs are brown, not wet, but I feel like I can get a little lighter brown on them while still being in the safe range. Just wanted to get some input from you guys to see where I can focus my attention. This is my first carburetor so I'm still learning all the bits and bobs. I know this is a forum for A bodies but I feel like the knowledge will still be pretty useful to me, and honestly I wouldn't be surprised if the weight between a Dakota and an A body were close enough where technically its "the same" in the eye of the engine.

 

[AJ/FormS]

that cam is 264/270/114; 212/218@050
The comp timing specs are impossible for me to get sense of, so I'm gonna assume that you installed it at about plus 3*, which is in at 111*
If that is true then your cam-timing events are;
264Int/117Comp/108Power/270Exh/39overlap/Ica of 63*
If you are getting 20" of idle vacuum, I can almost guarantee that the throttle is too far closed.

You cannot run like this in Virginia, at this time of year, especially at altitude, without a heated air intake.
What happens is that the edges of the throttles will form ice, and the engine will slowly choke. When you blip the throttle, some of that perhaps all, will break off, and disappear into the engine. Then it will idle fine for a few seconds and then it begins to choke again.

Reset your Idle-timing to 10*, increase your idle-rpm to 650 in gear, twiddle the mixture screws to best rich idle. Make sure the Secondaries are fully closed but not sticking. Make sure your PCV is plumbed to underneath the Primary throttles, which will help warm the incoming air, and finally, install a heated air system, that draws hot air directly off the exhaust manifold, into the airbox; exactly as the factory did.
IMO, you are attacking the rich-running from the wrong angle. see note-1
re-Install the original MJs of 66/71; leave the 6.5PV alone for now. Verify that your WET fuel-level is where the designer wants it to be, and that it STAYS there.
Now, fix your stall timing, see note-2
After that see the other notes.

Note-1
>Your low-rpm low-throttle-opening fuel-delivery system is;
the Transfers, plus a lil trim from the mixture screws. For the most part, this system is not adjustable.
> the PMJ comes on line at about 20>25 mph, when transitioning from steady-state cruise, to lightly accelerating. You can dick with the PMJs all you want, but at steady state, at 20 or so mph, they are NOT YET flowing.

Note-2
Your engine has three Ignition Timing Milestones. In order of importance, they are;
Power-Timing; usually about 34>36 degrees
Stall-Timing ; about 1 degree ; per 100rpm. If you have a M/T, consider this to be in the window of 2400>2800.
Cruise-Timing; depending on rpm can be 50>60 degrees
Idle-Timing ; not real important, except;
a) a tip-in sag sux. If yours does that, the throttle needs to be opened further.
b) banging into gear also sux. if yours does that, then retard the Idle timing. If you have a M/T, ignore this.
c) other than that, target 10>14, I say target.
Your job, as a tuner, is to marry those 4 points by modifying the distributor.
Power-timing of say 34*
If you convertor stalls at say 2400, Or if you have a M/T, then your target is 24*@2400.
If you need to run ~10* Idle-timing, then the D will have to add 34 less 10=24 degrees, install the appropriate cam.
After that, you need to connect 24@2400 to 34@3400ish, with rate of advance, which in this case is, ~1* per 100rpm.
Then connect 10* at Idle to 24* @2400 which is about
14* per 1600, which distills down to .88* per 100.
This is so close to 1* per 100 that you can just install whatever springs get you to ~1*per 100, then set your Power-Timing to 34>35, and let the Idle-timing be what it will be, she really doesn't care. Then roadtest, listening for detonation and modifying as may be necessary.

note-3
for winter, I would run the smallest radiator fan, on a thermostatic clutch, that gets the job done. This to reduce the draft over the carb/intake. and I would run a heated intake. With an electric assist choke. But if the AG is retained, then a manual choke.

note-4
After the Ignition-timing is fixed, now you can finalize your carb adjustments.

Note-5
lets talk about that cam.
Because of the very wide LSA, the compression degrees are just 117, and the power degrees are just 108.
That 117*, makes the Ica to be 63*
The Wallace Calculator predicts a cylinder pressure of just 144psi at 9.2Scr@900 ft elevation. And that means, that your 92 Dakota, may be be a lil sluggish off the line, depending on gears (and stall). Don't try to make it more than it is.
However, it also means, that the throttle is gonna need to be opened further during acceleration, all the time. and that is gonna suck gas.
Furthermore,
Assuming no headers, the Power stroke is just 108*, so when the Exhaust valve opens, there is still a good amount of pressure in the exhaust, which is pressure that should have/could have gone to the driveshaft; which sux gas.
Furthermore, your pistons have to pump those higher-pressure gasses, out of the chambers which, you guessed it, sux power and thus gas.
Therefore, for fuel-economy, your truck should have a high-efficiency dual exhaust on it.
But if you have headers, it might be worse, as the headers suck on the intake valves at the end of the exhaust stroke, which at low rpm, can suck thru the overlap cycle, all the way to the plenum and pull raw A/F mixture straight across the piston which is parked at TDC, and out the header it goes. Now, your cam, has a very modest overlap of just 39 degrees, but remember the factory 340 cars? Well they had just 5* more and were known to be gashogs. And guess what else; they had about the same Ica and just 104 degrees of PowerStroke.
The point is that you cannot expect that low-pressure combo to make fuel mileage. You need a different cam and/or more pressure.
And all the playing around with the carb, is only gonna get you drivability issues. Fix the cold-running issues, and fix the ignition-timing and engine-wise, that's as good as it gets.
At some point, I would try to take the Primaries down a jet or two (probably no less that 68), and kick up the PV to 10.5 which makes for a smoother roll on with a too-lean PMJ.

Note-6
These are my opinions; (both above and below)
As for me;
1) I would never install a 114LSA cam into an SBM, no matter what. All your fuel-economy problems could have been avoided with same cam ground on a 106>108 LSA.
2) Notta chance would I ever run cylinder pressure as low as 144psi, in anything but my winter beater.
3) Notta chance would I run less than a 2800 flash-stall.
4) I gotta have headers.
5) Notta chance would I run a rear gear less than the equivalent of 3.55s with 27/28 " tires.
6) if I had an overdrive, I would gear your combo to cruise at no less than 65= 2200
7) I would crank the cruise-timing up to 50>56 degrees, and see how she likes it.
8) I would try to run PT-timing a lil more than 1* per 100, from Idle to stall, and to prevent detonation; either
a) slow the rise after that, or
b) delay the all in to a higher rpm, as may be necessary
9) the 92 Dakota is a brick; I had one too, allbeit a lwb/extended cab/4x4/auto, and it sucked gas even as an MPFI/ A518/ 3.91s. Just make sure the brakes are not dragging, the alignment is good, and the tires are hard; what else can you do......
10) BTW, you said double pumper. I would Disconnect the secondary link and wire the secondaries shut; you may be surprised at how soon the Secondaries begin to come in.
On my hotrod, I designed an over-rideable primary throttle-stop, which I adjust to get me just enough throttle to cruise with. Thus I always know how far the Primaries are open. and Yes, when on the stop, it takes a really long time to come up to speedo
Ok so, I'm going bak to bed now, lol.
Happy HotRodding

 

[jmanhoff]

Holy cow that's a lot of information to digest lol.

I guess I'll add some more information if it helps you. I have the AX-15, geared to I believe 0.79OD, stock tire size 235/75r15 @ 41psi, and 3.55 gears which brings by 65mph rpm to actually probably about 2200. At 70 I'm at 2300. Vacuum advance is hooked to full vacuum, not ported. I still have the electric choke hooked up but I plan to swap over to a manual as I'm annoyed with how slow the choke opens when its warm outside.

You said a heated air system to pull air off the exhaust manifold like the stock setup did, did you mean pre-EFI Dakotas? I still have the stock intake setup minus the hose that went from the air cleaner to the radiator support so its pulling in air from the middle of the engine bay, there was never anything hooked to the stock manifolds (at least on my truck). I do have the PCV hooked under the primaries like you said. I also have the stock radiator fan that came on the Dakota, with a stock style clutch. As many other Dakota owners have said, this setup runs way too cold all the time. I think in the year and a half I've owned this truck I've only heard that clutch fan kick in one time and it was over the summer when I was running the v8 on EFI still, I was sitting at a light for 10 minutes when it was 105 degrees out and it kicked on when I started moving for maybe 15 seconds then it shut off and never turned back on. My temp needle never even makes it halfway on the gauge, always at about a quarter of the way up and with a laser thermometer it reads 150-160 on the radiator end caps. (This is with the stock v6 and the current v8.)

I do currently have shorty headers (can't run long tubes on a 4x4), but from them back its the stock exhaust with a flowmaster (not going to make a noticeable difference). I do plan soon to get the truck to a shop and have 2.5 inch pipe from the headers back with an h-pipe and magnaflow straight through mufflers installed.

Initially when I built the engine I planned to run the stock EFI, which is why I chose the cam that I did as it was "the largest cam you can run on the stock computer." And it ran (it didn't), but I looked into tuning and how much it would be and with my dad having a past of carbed mopars I said screw it and bought a carb. When I had the stock setup on the carb (#71 primary, #74 secondary, 6.5PV) and timing set at 12 degrees, on my drive from Fairfax to Radford it got 6mpg highway (yes you read that right). On my drive back for winter break a couple weeks ago, after having the #66 jets and timing at 14 degrees initial it got just about 16mpg hwy. On a couple of weeks worth of testing with the #68 jets I was getting 7mpg city/12mpg hwy.

Talking about the timing and throttle not being open enough now... I would imagine that when you say my throttle isn't open enough you mean my curb idle is way too low to the point that the transfer slot isn't being utilized? Fully warmed up with timing at 14 degrees, vac advance hooked up, the engine wants to idle super high, as such I lowered the curb screw not really thinking about it. Current idle is about 700rpm warm (though it fluctuates for whatever reason). If I'm correct in my thought process, if I turn the initial timing down to 10, then turn the idle mixture for a rich but happy idle (highest vacuum, back off eighth turn), and set the idle with vac advance hooked up to 800 or so would it open the throttle enough like you mentioned?

I really need to get an AFR hooked up, but when I ran the 68s, my plugs were black and I would see faint black smoke coming out of the tailpipe when on moderate throttle (before secondaries). To further prove my point about it being rich, on cold starts when there is condensation in the exhaust it literally will throw wet black soot onto the car next to me.

If any more info is needed please feel free to ask, I'm sure I can provide.

 

[RustyRatRod]

First off, let's correct something. It's NOT a Street Avenger. Those are Holley carburetors, not Quick Fuel and they are vacuum secondary, not mechanical secondary like the little Brawler that you have. So let's get that out of the way. What you have is a Brawler, 650 mechanical secondary (double pumper). Alrighty. Now we have that out of the way, I have a question.

WHY did you start by changing the jets?

 

[jmanhoff]

WHY did you start by changing the jets?

I think I got my carb names mixed up lol oops.

Anyway, I started messing with the timing and Idle mixture first, I tried 10, 12, 14, and nothing made a real difference. Timing is all in 31 degrees at about 2800, I haven't messed with the curve yet. I then went to the jets as I was burning through 20 gallons of gas every 100 miles, and being in college thats not exactly something thats easy to afford. I went into a long parking lot, opened up the throttle, turned it off, checked the plugs. Black and wet. So I ordered 68s, put them in, did the same test. No longer wet but still black, so I went to 66s and I'm where I am today.

 

[RustyRatRod]

I think I got my carb names mixed up lol oops.

Anyway, I started messing with the timing and Idle mixture first, I tried 10, 12, 14, and nothing made a real difference. Timing is all in 31 degrees at about 2800, I haven't messed with the curve yet. I then went to the jets as I was burning through 20 gallons of gas every 100 miles, and being in college thats not exactly something thats easy to afford. I went into a long parking lot, opened up the throttle, turned it off, checked the plugs. Black and wet. So I ordered 68s, put them in, did the same test. No longer wet but still black, so I went to 66s and I'm where I am today.

Well, it's never going to be a mileage miser. You may get it "better" but you bought a PERFORMANCE carburetor, not an economy carburetor. Secondly, the jets have zero to do with idle mixture, so if you're trying to make a difference with idle fuel changing jets, it'll never happen. The jets are on the power circuit, not the idle circuit. That carburetor is infinitely adjustable, as it has adjustable air bleeds on top, adjustable idle fuel restrictors in the metering block and adjustable power valve restrictors in the power valve circuit. You can get over your head REAL quick if you don't have experience tuning. My suggestion would be to invest in a wide band O2 tuner, read up on how to use it, get it installed and tune with that.

 

[jmanhoff]

Yeah I plan to get a wide band in the next coming weeks and use that for tuning, I was just curious if there was anymore useful input with my current situation.

Do these numbers sound pretty good for AFRs?
WOT: 13.0>
Cruise: 14.5-15.0
Idle: 15.0

I've been basing my jetting off of what the plugs tell me and how the exhaust smells, but I think with the right PV I can get away with running 64 primaries. It does fine under mild acceleration but started to get a little surgey when I put my foot down a little (coincidentally right around 9 inches of vacuum.) which is why I ordered a 9.5PV. I know every engine is different, but the fundamentals are the same which is what I'm trying to get a grasp of here.

 

[LO23M8B]

You have chock issues. Do you know anything about setting one up? What's the set up on it now and how about pics.

 

[jmanhoff]

You have chock issues. Do you know anything about setting one up? What's the set up on it now and how about pics.

If I recall correctly it’s currently set up as it was stock. Set to be fully open at 72 degrees according to the manual. I’ll take some pictures later today when it warms up a little more outside and I go to tinker with the timing.

 

[RustyRatRod]

Yeah I plan to get a wide band in the next coming weeks and use that for tuning, I was just curious if there was anymore useful input with my current situation.

Do these numbers sound pretty good for AFRs?
WOT: 13.0>
Cruise: 14.5-15.0
Idle: 15.0

I've been basing my jetting off of what the plugs tell me and how the exhaust smells, but I think with the right PV I can get away with running 64 primaries. It does fine under mild acceleration but started to get a little surgey when I put my foot down a little (coincidentally right around 9 inches of vacuum.) which is why I ordered a 9.5PV. I know every engine is different, but the fundamentals are the same which is what I'm trying to get a grasp of here.

Well again, the jets have ZERO effect at idle, so they will NOT affect the exhaust smell. So unless you're somehow hangin your head off the back bumper driving down the road to smell the exhaust, the only way you're doin it is at idle. Jets do NOT tune idle mixture. Where are you getting those readings from if you don't have a wideband yet? And btw, IMO, these are great little carburetors for the money. I have a 450 VS Slayer on the slant 6 in my 64 Valiant and I ran one same as yours on the 400 in my 75F250 for a while. It wasn't quite enough for it and I ended up with a Street Demon 750. I still have the Brawler, though.

 

[RustyRatRod]

Anyway....all that said, "MY" advice is to put the jets back stock for now and get the idle mixture sorted FIRST. Then move on to the power circuit. At least that's always worked best for me. I believe those come with .031 idle fuel restrictors. You'll need a magnifying glass.

 

[Newbomb Turk]

Those carbs are horrible out of the box. That’s just the truth. And they aren’t all the same tuneup from the factory.

The very first thing you need to do is move the idle feed restriction from the top of the idle feed well to the bottom. That requires some drill bits and taps. And some brass set screws.

You need 6/32 brass set screws for this. And the correct tap and drill.

If you do have an .031 idle feed restrictor I say that’s too big for what you are doing. I would drop it down to .028 and use a .070 idle air bleed to start.

Then you need to look at the emulsion stack. You should have four holes. The top and the third hole should be open and .028. The second and bottom hole should be blocked.

Do a search for T slot restrictors on the web. I use 10/32 brass set screws. You drill and tap the face of the main body for 10/32 and for that carb I’d start with a .070ish hole in the brass. You can tune it from there.

I wouldn’t use a main air bleed bigger than .026 but that’s me.

Also, you don’t need a heated intake manifold. I haven’t used one since 1981. Still don’t.

You have to get fuel out of it, and at this point you can’t do that by changing the jets.

 

[LO23M8B]

Dob't start it till I ask you to. Must be dead cold. Take the air cleaner off take a pic as it is now than hit the pedal one time and let it go and take a pic. Don't touch the pedal start it and quickly take a video of it. Run it till the choke fully opens. And if it runs bad and you have black smoke stick a large screwdriver , 6 inch or so in the choke blade to open it up some. And check the temp. outside. Forget all the other stuff for now, just forget it. You have a choke problem and that needs to be corrected first!

 

[jmanhoff]

The AFR numbers I listed were "goals" I was asking for opinions about if those were safe numbers, I should've specified that lol.

I'm about to go out and take those pictures for LO23M8B just have to let the truck roll down the driveway a bit so I don't smoke out my house haha.

I've set my idle mix several times and I still don't understand why its so rich on high idle. I've tried setting it with the vacuum gauge and the way my dad told me. "Turn the screws all the way lean until it starts to run rough, back off to where it clears up, then back a little more so its slightly more rich." I know that a choke richens the mixture but I feel like it's doing it way too much.

 

[LO23M8B]

Don’t let it roll on you. lol By the way if you have someone else around have them start it while you are videoing.

 

[Newbomb Turk]

The AFR numbers I listed were "goals" I was asking for opinions about if those were safe numbers, I should've specified that lol.

I'm about to go out and take those pictures for LO23M8B just have to let the truck roll down the driveway a bit so I don't smoke out my house haha.

I've set my idle mix several times and I still don't understand why its so rich on high idle. I've tried setting it with the vacuum gauge and the way my dad told me. "Turn the screws all the way lean until it starts to run rough, back off to where it clears up, then back a little more so its slightly more rich." I know that a choke richens the mixture but I feel like it's doing it way too much.

Don’t tune to an AFR number.

 

[AJ/FormS]

Well since you said that your Vacuum advance is plumbed to full-time vacuum, That could be your biggest enemy, cuz you didn't say how you set it that way nor how much the can brings in.

Notta chance would I run that modest cam on full-time VA.

 

[jmanhoff]

Well since you said that your Vacuum advance is plumbed to full-time vacuum, That could be your biggest enemy, cuz you didn't say how you set it that way nor how much the can brings in.

Notta chance would I run that modest cam on full-time VA.

I had it set to full manifold as opposed to ported from suggestions from a couple of people. I believe the can pulls about 26 degrees at full vacuum. It’s a MSD chinesium clone that didn’t specify. I need to take a peak at it once the engines warmed up. It did fix my off idle stumble when it was warmer but that’s when it was still 70 degrees, now it’s 30.

Here are some pics and will post the video in a minute.

Carb as it was when truck was shut off last night.

Throttle pressed to close choke.

Current choke setting, it’s hard to see but it’s on the second from the right, set to open sooner.

 

[jmanhoff]

Here is the startup video.



Ignore the ticking, it’s a pushrod issue and I have non adjustable rockers

 

[James Clews]

For a start that carb is on backwards! Depending on manifold that could be a problem right there!

 

[jmanhoff]

For a start that carb is on backwards! Depending on manifold that could be a problem right there!

I didn’t really think that the orientation mattered honestly, I mainly did it this way because I wanted my fuel line tucked against the firewall and wanted to retain the stock throttle cable for time being which was routed the same way it is now, around the front of the engine to the passenger side.

Looking at pictures of the throat of the intake it doesn’t really seem like it’s important which way it goes, front to back it looks symmetrical. I think if I for some reason mounted it sideways it would be a different story.

 

[RustyRatRod]

I didn’t really think that the orientation mattered honestly, I mainly did it this way because I wanted my fuel line tucked against the firewall and wanted to retain the stock throttle cable for time being which was routed the same way it is now, around the front of the engine to the passenger side.

Looking at pictures of the throat of the intake it doesn’t really seem like it’s important which way it goes, front to back it looks symmetrical. I think if I for some reason mounted it sideways it would be a different story.

It matters.

 

[jmanhoff]

Alright well that’s a start lol. I guess I’ll have to order a throttle cable kit and flip the carb around. Do you guys think it would be worth getting a manual choke? I know those aren’t reversible once installed. At least from what I can tell with the lead ball.

 

[RustyRatRod]

Alright well that’s a start lol. I guess I’ll have to order a throttle cable kit and flip the carb around. Do you guys think it would be worth getting a manual choke? I know those aren’t reversible once installed. At least from what I can tell with the lead ball.

What "I" would do UNTIL you get the carburetor tuning sorted out is adjust the choke plate ALL the way open and lock it down. That way, there's no chance of it influencing your tune.

 

[Hysteric]

Pull the spark plugs out and look at the centre electrode surface where the spark jumps across and post some photos.