Solving a lean spot off idle, rich everywhere else

CDXXVII

CDXXVII

New member
I might have to send the carb back as I'm both washing the cylinders and also detonating.

427ci
Manual trans
.638/.622
243/255 @ .050
Dual plane intake
Promaxx project x 210 heads
10.4 compression
Currently 19 initial 32-33 total timing By 2600
no vacuum advance
heaviest msd springs
Ngk 6 plugs, showing timing mark way down the apex, and getting speckled.
ATM 850 with annular boosters

Set up from ATM with:
35 nozzles
33 high speed bleeds
75 idle air bleeds
33 idle feed restrictions
6.5 power valve
.084/.099 jets.

950rpm warm idle
9" vacuum
13.0 afr

Rowing through gears normal acceleration 11.5 to 12.0 afr

Steady mph no load high 11s afr
19-20" vacuum cruising 1800 to 2000rpm

Easing into throttle to keep up with traffic, lean spike 16-18 afr, and detonation. Detonation will continue if I hold throttle in that position, but no lean spot if I blip throttle (like getting going from stop light easing off the clutch)

Wide open 10.7afr

Seems to me the transition slots Are running dry when barely tipping into throttle. I was going to change IFR and see, then IAB.. but I've been advised that I'm getting to the point of fucking the engine up. Only 40 miles on the new build and wayyyy too much idle time trying to fuck with things.
 
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A post from whitener I found many years ago said try raising primary floats

Not sure what you mean how does it run. Rich. Slow. Luggy maybe.

It's all relative as this is my first carburetor and first "500hp" engine but it sure doesn't pull like a train or act like it's on ice skates. One or the other should be true, so I'm kind of not the right person to ask.
 
Cruise with a cam like that will probably be happier a few hundred RPM higher.

Have you thought about swapping on the 650 on to see how it runs?
It that a vacuum secondary?
 
That brass piece in the emulsion stack?? (please tell me what it's called) is a plug, no hole.

Removing the plug there is a small hole behind it. All 4 holes in each side have those small holes
 
I was just going to ask that!

They are odd blocks.

So what you have is three emulsion holes vs the two that I talked about.
They're kind of semi-adjustable, meaning the holes are fixed, but you can install a set screw that has a smaller hole.

Is the highest of the four holes about the level of the fuel in the bowl?
 
Even people who are pretty good at this stuff are iffy about messing with emulsion.
That said, what they generally say is leave it like the original Holley setup.
It should be pretty easy in your case.
Leave the highest hole as is and plug the second from the top.
Then leave one of the two lower holes open.
So, you'll need another blank set screw on both sides.

Looking at the block, I'd say leave the existing plug where it is.

So... all you need to do is screw a 6/32 set screw or whatever it's tapped for into the second from the top and see if that helps.
 
CDXXVII said:
That brass piece in the emulsion stack?? (please tell me what it's called) is a plug, no hole.

Removing the plug there is a small hole behind it. All 4 holes in each side have those small holes
Click to expand...


Yep that’s a plug

You really need to know what size those holes are.

The magic setup is .028 plug .028. plug or something like that. It is the original 60’s double pumper calibration.

The IFR needs to be in the bottom of that channel.

You will need taps, itty bitty drill bits, a pin vise & an assortment of blank bleeds so you can map what you have & fix it yourself

McMaster Carr has all the stuff

Read all about it in here:
https://www.tapatalk.com/groups/racingfuelsystems/index.php

This is a very VERY smart carb guy’s forum.
 
willisonTfosdik said:
Yep that’s a plug

You really need to know what size those holes are.

The magic setup is .028 plug .028. plug or something like that. It is the original 60’s double pumper calibration.

The IFR needs to be in the bottom of that channel.

You will need taps, itty bitty drill bits, a pin vise & an assortment of blank bleeds so you can map what you have & fix it yourself

McMaster Carr has all the stuff

Read all about it in here:
https://www.tapatalk.com/groups/racingfuelsystems/index.php

This is a very VERY smart carb guy’s forum.
Click to expand...
Legitimately why wouldn't the company that designs and builds these do it that way out of the box. At this price point you'd think they'd have more than the basics figured out
 
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