Lean spot from 1800 to 2,500 light throttle

[lorax]

Unless the OP states that the vacuum drops below 12 or 10.5 or whatever PV is installed, I don't see how it can help. If the carb is jetted and PV'd to "perfect" AR when the PV is open, & WOT, it can only be leaner if its closed. I believe that's the point of the PV. I never used one to cover lean spots at steady cruise and light acceleration from 1800 to 2500. If the lean spot occurs when there is 13-16 of vacuum, how does the PV help.
I don't think I want my PV opening every time I tickle the throttle a hair. Bad enough the accelerator pump pushes a little fuel each time.

[zums]

sounds like your starting to drink the pv coolaid

[lorax]

sounds like your starting to drink the pv coolaid

Not on your life. But you remember posting this question:

who said anything about fixing it with a pv

Well the answer is 2 posts after your first post, and 6 post before you asked.
5 pages later, it is gaining speed.

[GARY C]

Page 5, so I'll ask again...

Being the dumb one that I am I have to ask, what engine, cubic inch, compression, head and intake runner cc, and complete cam specs...Type Hyd or solid flat or roller and specs, duration on seat, @.050 and LSA as well as installed centerline????
What car and rear gear?
Idle rpm and vacuum?

[MadBill]

Late to the party as usual, but has anyone noticed that "knowing more than 99.99% of the people in the world about Holleys" puts one in a less-than-exclusive club of seven hundred thousand people? (Seven billion times 0.01%)

[GARY C]

If it were me I would do something stupid like mounting a go pro camera over the carb to see if it's still on the transition circuit or if the mains are starting to come in... then again if it drives fine i wouldn't even worry about what a gauge is telling me.

[n5ifi]

Late to the party as usual, but has anyone noticed that "knowing more than 99.99% of the people in the world about Holleys" puts one in a less-than-exclusive club of seven hundred thousand people? (Seven billion times 0.01%)

Only 10 out of 100000 can do any kind of serious carb tuning. Most have never heard the term "emulsion, air bleed, booster or carb". Most think we are talking about carbohydrates when we say carb.

700000 * .0001 = 70

All of these people are registered here so we are in good hands.

[n5ifi]

If it were me I would do something stupid like mounting a go pro camera over the carb to see if it's still on the transition circuit or if the mains are starting to come in... then again if it drives fine i wouldn't even worry about what a gauge is telling me.

What's the frame rate on those cameras? It would need to be a bunch.

I'll bet the mains are in by 2500 though, surely......?

[lorax]

Late to the party as usual, but has anyone noticed that "knowing more than 99.99% of the people in the world about Holleys" puts one in a less-than-exclusive club of seven hundred thousand people? (Seven billion times 0.01%)

Only 10 out of 100000 can do any kind of serious carb tuning. Most have never heard the term "emulsion, air bleed, booster or carb". Most think we are talking about carbohydrates when we say carb.

700000 * .0001 = 70

All of these people are registered here so we are in good hands.

That's some basically good stuff guys

[lorax]

If it were me I would do something stupid like mounting a go pro camera over the carb to see if it's still on the transition circuit or if the mains are starting to come in... then again if it drives fine i wouldn't even worry about what a gauge is telling me.

What's the frame rate on those cameras? It would need to be a bunch.

I'll bet the mains are in by 2500 though, surely......?

I would agree the main is active by 2500. I think the question is, is the idle/transition on its way down and the main on it way up, and the transition over lap is just not correct. Isn't this what Mark and Tuner have refered to as the smoothness of the transition in regards to the emulsion/air bleeds in concert with the idle/transition? Maybe I misunderstood.

[lluciano77]

Page 5, so I'll ask again...

Being the dumb one that I am I have to ask, what engine, cubic inch, compression, head and intake runner cc, and complete cam specs...Type Hyd or solid flat or roller and specs, duration on seat, @.050 and LSA as well as installed centerline????
What car and rear gear?
Idle rpm and vacuum?

SBC 400
11.25:1
220cc intake
Victor Jr.
234/244, .576/.593", 112o lobe hyd roller
73 Camaro, th350, 3.42
12" idle vacuum, 750 RPM

Or as for the cruise vacuum where the problem occurs and the PV rating. The vacuum gets close but doesn't dip into 10.5" under the problem conditions. It mostly hovers in around 12". The engine is still making a fair amount of torque to move the car, and the vacuum advance is pulled all the way at its 5 degree advance setting. I am only at 5 degrees vacuum as it would start to ping any higher than that at cruise in the 1800 to 2500 range. At 8 degrees it was barely noticeable, so I backed it to 5 to be safe.

So far it seems that maybe the way to go is increase the IFRs a little and try to cover the hole there. I am guessing at that point to try and re-balance the idle mixture across the board with a .030" IFR, and increasing one or two IAB sizes if needed after that.

The float levels... I am at the center line on the float bowls of the Demon. I can try raising the floats a little, then taking the car out for a run to see if it helps before messing with the bleeds. This would be easy to do and easy to reset. But the main thing is that every where else the carb is spot on, which is why I am trying to fill the lean gap I am having other areas affected.

[jmarkaudio]

On when the mains start, that is a big variable that depends on several things. At what point does engine vacuum in relation to throttle position come up enough to start main flow. Cam profile has a lot to do with that. How big the butterflies/carb is has an effect, the larger they are the more delay before the mains get enough signal. With two carbs and one to one linkage the delay is even higher. I have seen boosters start as low as around 1800 RPM, and upwards of 4000 RPM. Transition circuit metering needs to be adjusted to cover either end or anywhere in between.

[RednGold86Z]

(inserts comment about EFI ... some people think carbs are easy and EFI is hard ???)

Is 14.5 really surging on the car??? Don't worry about the lambda meter if it's not giving drivability problems. It won't hurt a thing if that's what you're worried about, as long as your full throttle stuff is sorted.

[MadBill]

Whoa, R&G; I skimmed over that reference to 14.5:1 in the O.P. and focused on 'lean'!
For the record, 14.5 is nothing like 'lean' for part throttle cruise. All but the most radical-cam or mismatched component engines will happily cruise at that. Many will run fine and deliver great mileage as much as 2 full ratios leaner still.

Sounds like the "If it ain't broke, don't fix it" adage may apply here...

[lluciano77]

The part throttle cruise is okay in the 1800 to 2500 range. It is when trying to give it more throttle, like passing other cars in traffic for example. You can feel the RPMs not wanting to climb steady. I wouldn't say it is surging. Just super flat on power. If I keep pushing the throttle past it, it will eventually after 2,500 start richening and making power again. If I add more vacuum advance in the posted range it will ping.

My engine tolerates 15.5 at light cruise without surging and without load of course. Not focused completely on wideband readings, but I am sure going at least into the 13s would be better under this higher load. Sometimes it will get there. When the car starts moving without this bog, I have noticed on rare occasion that the afr is richer.

My converter is rather tight at 2,400 stall. I am trying to avoid going any higher to keep the car more streetable, and not band aiding past the flat spot with more stall. Also with the gearing at 3.42 and a 28" tall tire, I am sure a 3.73 would help....but be less streetable as well.