Thrust issues with AFR gauge and Brawler carb

[Newbomb Turk]

Not sure what happens at beginning. Acceleration pump seems to have its own issues, when I press gas lightly at any speed it goes momentarily leaner and after that start to accelerate properly.

You are correct. He’s something I had to learn the hard way.

There is a puddle of fuel at the bottom off the intake manifold.

I can’t explain it nor do I have even a rudimentary understanding of it. Yet.

But there is a puddle and that puddle gets upset and moves with G forces. The way I understand it is that any sudden opening of the throttle blades drops the pressure in the intake tract. Any vaporized fuel becomes liquid again and it adds to the puddle and the puddle ends up dumping and you get a rich spike even it could be lean.

I’ve watched that Jon Kaase video over and over until I can’t see and I can’t see a puddle.

BUT, if you watch closely you’re A/F ratio you are logging you will see how the puddle influences A/F ratio on a running engine.

The upshot is my dumb *** should have paid more attention in school.

 

[Hysteric]

Hard to tell from those photos but most likely an ignition issue. When the calibration is close to stock then I would suspect ignition.

I've seen a 0.5v drop in alternator voltage output change the burn to make it look rich when the AFR didn't change.

 

[Newbomb Turk]

Hard to tell from those photos but most likely an ignition issue. When the calibration is close to stock then I would suspect ignition.

I've seen a 0.5v drop in alternator voltage output change the burn to make it look rich when the AFR didn't change.

I agree but when he has four open emulsion holes and that AFR graph he needs to clean that up first.

But I agree the ignition looks a bit weak. I just didn’t want to blow him up with more stuff. I know it gets overwhelming.

 

[Dusterguy]

I agree but when he has four open emulsion holes and that AFR graph he needs to clean that up first.

But I agree the ignition looks a bit weak. I just didn’t want to blow him up with more stuff. I know it gets overwhelming.

How did you figure out that ignition might be weak? I did a voltage measurement from ballast resistor that is blue ignition on- wire. While ignition key on, it showed excessive voltage drop about 2 volts (between battery and ballast resistor). I have already bypassed the bulkhead connector from firewall. I need to figure out where the problem is.

I ordered pin gauges and emulsion jets. Might take few weeks until I get them.

 

[Mattax]

I did a voltage measurement from ballast resistor that is blue ignition on- wire. While ignition key on, it showed excessive voltage drop about 2 volts (between battery and ballast resistor).

With key on, engine off, there should be very little voltage drop because the only current moving is to power alternator field, the coil (and ECU if there is one). If the ammeter shows more than 5 amps discharge then something is wrong (or there have been modifications).

With the engine running, the voltage difference between the alternator output and the VR input (ign terminal) should be small. Less than 0.5 volts. With an electronic ECU, the closest place to measure is the ballast resistor ignition run wires (J2 blue with stripe), the bulkhead connector, or the alternator's field terminal wire (blue, from ignition). The power source is the alternator. Measure from there. Make the voltage drop measurement after the battery is recharged.

Do a search for more about this. I'm short on time to type. Sorry.

I have already bypassed the bulkhead connector from firewall. I need to figure out where the problem is.

Losses in the steering column connector are common, and on some years there is a also an engine connector.

I ordered pin gauges and emulsion jets.

Good.
Always good to measure out the carb restrictions and placements.
Some details on excessive emulsion here racingfuelsystems-Emulsion Tuning
Bottom line is two is enough, especially with a kill bleed. As long as they are not too big
Three is OK if they are small enough.

Seeing it drop stepwise rather than taper suggests it may not be a jetting or air bleed issue.
Being in second gear it may only be hitting load part way up the rpm. Load slows the engine, adds heat, and is the engine condition that really matters at WOT.

As far as the AFR numbers, they make sense. Rich idle. Leaner off-idle light load, low throttle. Leanest moderate throttle acceleration. Then rich approaching full throttle.

racingfuelsystems-Desired Carburetor AFR Characteristics At Different % Load

The clue here is rich idle, lean cruise, leaner (leanest, actually) part-throttle acceleration and rich WOT. The leanest is at mid-load, half-throttle

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