If the device does this, surely then the decel won't be the same? The coast distance lengthened I should think. It might need to be given some form of add-on timing control?
The Carb Cheater
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Also could (probably would) cause audible exhaust backfires. Loud ex. backfire indicates a lean condition often caused by extra air getting into the hot rich unburned fuel in the ex pipe.
The only moment I'd like added air is at the moment of pedal release. The flooding sag on big volume intakes annoys me. The DP is bad about it. Have imagined a vacuum controlled valve. Any vacuum over, say, 21", or a sudden increase of vacuum, it opens briefly and lets a gulp of air in. Just long enough to clear the dense charge in the intake. The '70's dashpots that held the throttle slightly open for a second or so would suffice if I could find one that would adapt to the Holley. . Meanwhile, we drive on with it like it is "and always has been". Still like my 3 carb'd vehicles.
I saw the videos of the carb cheater, and I think the idea is great. The only thing that would annoy me is the sucking noise of the air valve, to me it sounds somehow wrong. But maybe it isn't as bad in real life as heard in the videos.
Extra work and maybe overkill- remove the little filter and run a hose from the controller to inside the carb airfilter housing.
Great discussion!
I usually start my carb tuning on the rich side and I’ll keep leaning the jets until the motor starts to miss in normal driving. I’m wondering if a manual transmission motor is more likely to miss than an automatic trans?
It would be interesting to know at what fuel mixture does the miss begin.
And would the CC over correct for the power valve operation.
I usually start my carb tuning on the rich side and I’ll keep leaning the jets until the motor starts to miss in normal driving. I’m wondering if a manual transmission motor is more likely to miss than an automatic trans?
It would be interesting to know at what fuel mixture does the miss begin.
And would the CC over correct for the power valve operation.
That's a good question. It probably couldn't overcome the power circuit since it's merely a controlled vacuum leak, and there's low vacuum in the power circuit. It couldn't add any air @ WOT.
PSIG
Famous Member
If you are leaning to the point of detectable misfiring, you're going much too far in one jump. All fuel tuning is to max-torque, except for decel of course, and cruise fueling at various speeds - so I assume that's what we're looking at here. To use lean-cruise tuning with a 'smart' controller such as the Carb Cheater, follow all steps except leaning from slightly rich, which will be with the CC.
Tuning requires stable conditions of fully-warmed engine temperature, normal fuel choice, etc. When tuning cruise fueling, you would carefully maintain your steady and constant specific cruise speed target on each test run, same level road, weather, etc. You would typically tune "bottom-up", from idle and work to higher speeds and loads, building the tune one area on the last, so the next tuning would normally be transition circuits. Those are varied and can be complex on certain carbs (see documentation for your brand and model), so let's jump past those only for sake of this example.
The target speed could be your max highway cruise, where your main jet(s) should be the primary fueling source. You can jump multiple jet sizes or bleeds to quickly find lean misfire, then richen back up to the last smooth-running jet size.
From there, return to leaning but by smallest steps (or with the CC if that's what you're using) until you begin to feel a slight and slow push-pull surging of power (with no movement of pedal or change of conditions). This mild surging is the onset of partial misfire (incomplete burn) in the weakest cylinder. You will feel no "misfire". As the lean-surging slowly cycles (once per few to several seconds like a shifting light headwind), the manifold vacuum can be seen to also wave slightly higher and lower, which is the source of the cyclic surge and recovery cycle. If using a Lambda/AFR gauge, you will also see the AFR waver, as the partial misfire adds O2 to create a leaner-than-actual reading. Reminder - misfires (even excessively rich misfire) will read leaner due to the extra oxygen in the un-burned exhaust.
You have found and slightly crossed the lean-burn edge. Richen one step and you're there.
Repeat at various cruise speeds, altering the circuits that apply most prominently, such as the transition circuit at lower cruise speeds, and re-check other speeds, as the effects of each circuit add and overlap.Note before you run off to do this, your idle should already be tuned to the maximum vacuum you can attain at your normal warm target idle and correct timing, as idle tuning will affect cruise tuning. Also verify your power enrichment circuit(s) are not functioning at your max cruise speed, typically above about 80% throttle. For example, if your carb uses a power valve to enrich for power, test it for function and opening vacuum, noting the vacuum reading that it cracks open. This vacuum level should be slightly higher than your max highway cruise vacuum, or your economy will suffer greatly. Likewise, a "smart" control unit may be trying to lean your power fueling rather than maintaining it at safe peak-torque fueling in that condition. Your carb, ignition, and smart controllers must work together.
Finally, and very important - after finding your lean-burn cruise fueling, you must correct your cruise ignition timing. This can only be done (easily) with a standard vacuum-advance distributor or programmable ignition, and will both increase your efficiency (economy) and reduce any late-burn heating effects (the "lean is hot!" stories). I will make a separate post for how to correct and restore the optimal cruise timing.
@Moderator - should this and following be in a different section?
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excellent explanation!
My current issues are with a 240 , 4 speed od rug transmission and constant hills. It’s difficult with this transmission to find a good gear for cruising up these hills. I depend a lot on the power valve to deliver the extra shot to climb the hills. I’m using a Holley 5210 carb. These carbs only have the power valve on the primary barrel so the tuning of the secondary needs to be a bit rich since I need the secondary only for the more steep climbing.
I don’t know how the CC would react to a progressive 2 barrel carb.
My current issues are with a 240 , 4 speed od rug transmission and constant hills. It’s difficult with this transmission to find a good gear for cruising up these hills. I depend a lot on the power valve to deliver the extra shot to climb the hills. I’m using a Holley 5210 carb. These carbs only have the power valve on the primary barrel so the tuning of the secondary needs to be a bit rich since I need the secondary only for the more steep climbing.
I don’t know how the CC would react to a progressive 2 barrel carb.
I'll say again, it may influence the secondary operation some, but depending on how much vacuum is present. What it would help with is when coming off-throttle out of the secondary, it should soften the rich spike that occurs there. With the log intake this spike is less in duration and intensity over a larger plenum intake. On the DP intake and 4V the engine actually flood-bogs if the pedal is lifted quickly from heavy throttle. Since vacuum is restored at this moment, the CC would be a noticeable aid during this plenum transition out of the power circuit.
You need a wideband A/F tester so you can get the carb jetted properly.
WOT with ethanol in the 12.3-12.5 area. Cruise 14.3-14.5 area.
Non ethanol 12.8-13.1 area. Cruise 14.7-14.9 area.
Doing this you can curve the distributor for maximum power & economy.
WOT with ethanol in the 12.3-12.5 area. Cruise 14.3-14.5 area.
Non ethanol 12.8-13.1 area. Cruise 14.7-14.9 area.
Doing this you can curve the distributor for maximum power & economy.
PSIG
Famous Member
Is that lifting to closed-throttle, or just lifting to high-part-throttle? Rich after lift is common, due to wall-wetting in the runners and reduced airflow to carry it to the cylinders by then. The flow it does have is already at good fueling from the carb, so the extra fuel that's wall-wetted gives a momentary rich at part-throttle, and considerably longer over-rich at closed throttle. Typical of wet-manifolds but worse, of course, with long runners. Is that what you're seeing?
I’ve been considering buying one. Any recommendations?
I've been looking at them for a while. There seems to be consensus that the Bosch sensor is the best by far and to make sure the kit includes that brand. Auto Meter gauges are well rated all around but aren't the cheapest.
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Yes. It is compounded by the design of the Offy Dual Port intake.
PSIG
Famous Member
Part of the purpose of dash pots was to limit closed-throttle decel over-rich. It won't help part-throttle enrichment, but may help or solve full-lift issues. Do your have any throttle solenoid or pot on there now?
Electronic controls (and most EFI controllers) can have a "dash pot" or "decel air bypass" function that can do the same, simply going immediately to a specific IAC setting of steps (effectively as "high idle" opening) to accomplish the same effect. I don't know if the CC has such as function. EFI controllers usually accomplish this using a deceleration fuel cut or reduction, to limit the fuel before it's an issue, rather than clear it when it is; but is an additional option anyway for setups such as TBI.
Electronic controls (and most EFI controllers) can have a "dash pot" or "decel air bypass" function that can do the same, simply going immediately to a specific IAC setting of steps (effectively as "high idle" opening) to accomplish the same effect. I don't know if the CC has such as function. EFI controllers usually accomplish this using a deceleration fuel cut or reduction, to limit the fuel before it's an issue, rather than clear it when it is; but is an additional option anyway for setups such as TBI.
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Thanks. Aware of all of the above. One distinct advantage of EFI is decel rich elimination, for sure. Outside of EFI there is nothing that can be done about it with my combo. (Except something along the lines of carb cheater.)
The Offy DP intake has more negatives than positives in the real world.
All Big Six - Offenhauser Dual Port (DP) Intake Manifold
Offenhauser has designed and produced some of the most creative and effective performance intakes ever made. If one is old enough to remember, there have been some very out-of-the-box designs. A very long tube, dual 2V carb design for V8 Mopar engines comes to mind. This thread is not bashing...
fordsix.com
Joe - CC
New member
Joe here, the guy helping Luke (Thunderhead289) build the Carb Cheater. Happy to answer any questions about it.
Here's a picture of my dad's F100 with a 300 i6 hauling around 150 carb cheaters into the post office in town. Hell of a work truck.
photos.app.goo.gl
Here's a picture of my dad's F100 with a 300 i6 hauling around 150 carb cheaters into the post office in town. Hell of a work truck.
New item by Joe Ternus
photos.app.goo.gl
Rod Beauvex
New member
I think someone mentioned Honda, but is this not also what Chrysler's feedback carbs did, called the lean burn system?
I like the fact these guys essentially built the exact opposite of this thing.
I like the fact these guys essentially built the exact opposite of this thing.
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