Rich wot but reducing secondary jets isn’t helping?

[Sonny]

Specs:
440 1970 Belvedere with 276 highway gears

Holley 4160 750 cfm, heavy vac spring, added 4150 conversion kit, jets prim 68, sec 66! 4.5 power valve

dual plane, Edelbrock

mild-ish cam (.5 lift),

Keith black raised pistons, stock 452 heads

msd dizzy with blue and light silver spring, timing 18/35

Bought a new Holley 750 and runs good but wot air fuel ratio is 10-11, way to rich. So I bought the 4150 conversion kit and removed the 75 plate and installed 71 secondary jets. No change. For giggles went to 66s. Same no change. Reduced squirter from 31 to 28. Nothing. How is this possible?

Could it be:
1. The gears are so slow that the engine can’t rev enough to burn the fuel?
2. I’m using a hp fuel pump (up to 9 psi) and a cheap mr gasket fuel pressure regulator and 1/4” return line. Could the pump still be overcoming the needle with higher rpm and flooding? I have a Holley pressure regulator with a gauge port on the way from summit racing to see if this is it.

Any other suggestions? Due to the cars gearing and weight, I added the heavy vac secondary spring, lower power valve, and medium dizzy springs to delay the “all in” fuel.

 

[dla4567]

Jets don’t do much to adjust wot mixture. That is mostly the size of the power valve ports. Some are adjustable, most are not.

 

[dla4567]

 

[Sonny]

Note there is no secondary power valve With the 4150 upgrade.

 

[RJRENTON]

Gentlemen,
I disagree wholeheartedly with DLA4567's premise re "jets have nothing to do with mixture volume"....they have everything to do with the mixture volume. In fact they supply 90% (+/-) of the fuel flow. The secondary power valve is just a valve...its either open or closed. The ports on the power valve fo not meter the fuel but just provide a window to the POWER VALVE CHANNEL RESTRICTIONS, which are the metering element. They are pressed into the metering block and are calibrated orifices that are not changeable except by drilling larger or soldering closed and redrilled to a smaller size. Typically, these orifices are in the 0.030" - 0.040" diameter range (depending on application). Power valve number is the OPENING POINT (vacuum signal) of the valve that exposes the channel restrictions to the emulsion wells, where the liquid fuel is first mixed with air.
I'm not sure why most guys run high fuel pressures only to reduce it to 5-6 # at the carb. Increasing fuel pressure does not necessarily increase fuel VOLUME. Fuel pump volume is determined by the design of the pump's stroke and diaphragm area (displacement). Anyway, this is just my opinion.
Bob Renton

 

[dla4567]

Gentlemen,
I disagree wholeheartedly with DLA4567's premise re "jets have nothing to do with mixture volume"....they have everything to do with the mixture volume. In fact they supply 90% (+/-) of the fuel flow. The secondary power valve is just a valve...its either open or closed. The ports on the power valve fo not meter the fuel but just provide a window to the POWER VALVE CHANNEL RESTRICTIONS, which are the metering element. They are pressed into the metering block and are calibrated orifices that are not changeable except by drilling larger or soldering closed and redrilled to a smaller size. Typically, these orifices are in the 0.030" - 0.040" diameter range (depending on application). Power valve number is the OPENING POINT (vacuum signal) of the valve that exposes the channel restrictions to the emulsion wells, where the liquid fuel is first mixed with air.
I'm not sure why most guys run high fuel pressures only to reduce it to 5-6 # at the carb. Increasing fuel pressure does not necessarily increase fuel VOLUME. Fuel pump volume is determined by the design of the pump's stroke and diaphragm area (displacement). Anyway, this is just my opinion.
Bob Renton

I did not say “jets have nothing to do with mixture volume”.
My point was that you don’t change jets based on wot. If the jets are sized correctly (for part throttle), then what you get at wot is due to the size of the power valve ports. I could have written a lot of words to explain it, but instead attached a video that I thought would be helpful instead.

 

[HEMI-ITIS]

OP states there are no PVs.I am no expert but the only way to lower AFR @ WOT is either jet or HSAB,,,right?

 

[Sonny]

OP states there are no PVs.I am no expert but the only way to lower AFR @ WOT is either jet or HSAB,,,right?

The is a power valve in the primary, but not the secondary.

 

[HEMI-ITIS]

Do you have logging ability or just a gauge?

 

[RJRENTON]

DLA4567,
I totally disagree with your premise. I ALWAYS correct jetting (up or down) based on W-O-T conditions (spark plug readings, time slips or engine dynamometer horsepower curve readings or individual cylinder exhaust gas temp readings). The Windows on the power valve (when open) allow the the fuel to flow to the CHANNEL RESTRICTIONS.
As l recall, 4150 conversions ftom 4160 carbs require either installing a power valve plug or sizing the main jets to get the correct secondary mixture. Anything less than WOT will likely result in the secondary butterfly valves remaining closed. Carbs work deferential pressure based on primary secondary air flow.
Bob Renton

 

[Sonny]

Do you have logging ability or just a gauge?

View attachment 787259

That’s a great idea. I don’t have a logger, but I have a laptop and the wire connection. I’ll see! Thanks

 

[steve340]

You are basing all your observations on an electronic gauge.
Are you sure it is correct?
I would also be checking the plugs.
By the way jetting has everything to do with how rich or lean the mixture is.

 

[Sonny]

You are basing all your observations on an electronic gauge.
Are you sure it is correct?
I would also be checking the plugs.
By the way jetting has everything to do with how rich or lean the mixture is.

I checked my plugs. They are white. I think my gauge is a liar and a fat mouth. Holley tech told me the same thing. Going back to 72s and will check again. Thanks.

 

[HEMI-ITIS]

I checked my plugs. They are white. I think my gauge is a liar and a fat mouth. Holley tech told me the same thing. Going back to 72s and will check again. Thanks.

The proper way to read the plug is to kill the ignition @ WOT at least in the top of 2nd or at the stripe when at the dragstrip.
WARNING! You must wait 'till things cool off before attempting to remove a spark plug,,,,,,,unless itsaHEMI!

Several plugs from several 1/4 mile passes.

 

[POMONAMISSEL]

what ignition are you running . could cold sparken are wot .

 

[HEMI-ITIS]

what ignition are you running . could cold sparken are wot .

Your right Paul,those plugs were too cold.

 

[Wietse]

Could it not be that due to the heavy spring on the vacuum secondary the secondary's not fully open?
Maybe reinstall the medium spring and try again?

What readings do you get at part throttle with only on primary's?
If that is also rich you could reduce a size on the primary jets?

 

[Sonny]

I have 13.0 to 13.5 on light throttle cruise. If I get over 14.0 I get minor lean surging.

I’ll try a lighter vac spring. The assumption is if the secondary is closed but the pv is open, it would run rich? Sounds logical to me! I’ll go very light spring and see.

 

[steve340]

Go back to the standard secondary spring. With the light spring it may open too early and you will get a bog as it opens and goes rich.
You say you have 2.76 gears you want the secondary to not open too soon.

 

[Wietse]

I believe all carbs will come with a medium spring installed, then if required the lighter or heavier spring can be used.
Stock settings will work with most applications, the light spring would be more for radical cams with poor vacuum.

The fact that changing jets is not doing anything made me think of what could cause a lack of air, but i am not sure if this is the right thinking.