*****UPDATED, SEE BOTTOM POST #23*****


Okay, so I got a Skip White 406 short block and added AFR 1054 heads, Victor Jr. intake & Quick Fuel 850SS carb (as recommended by S.W.) It is 10.4:1 compression.

After running only a 12.9 @ 106 I thought something was wrong.

So I got a wideband o2 sensor hooked up & the a/f gauge reads 12.5 - 12.9. That's great but....

It is running rich under acceleration. From the point of even touching the pedal and accelerating, it drops down to between 10 & 11:1 and stays there until I let off the gas to where it returns to the 12.5 - 12.9 range.

The carb has size 85 jets. Any thoughts? I would hate to mess with the mixture screws to screw up the idle/cruising performance to compensate for wide-open throttle performance. It would be nice to see and use full potential of this motor. Thanks in advance!

 

There are several potential causes but a bit of testing will isolate the source, at this point it sounds like the power valves adding too much fuel too soon, Id suggest leaning it out a bit and check your fuel pressure is consistent at the carb inlet port and float levels are correct, if your not running a return style fuel pressure regulator it may be related to fuel flooding the fuel bowls as the throttles opened rapidly allowing the needle/seat to open and fuel pressure holding it open longer than ideal. if your cars got a fuel pressure gauge Id suggest setting the carb inlet pressure at 4.5-5 psi,and checking your fuel bowl float levels.
don,t guess do a few tests and document the result of changes made.



http://forum.grumpysperformance.com/...hp?f=55&t=1639

http://forum.grumpysperformance.com/...php?f=55&t=109

http://forum.grumpysperformance.com/...php?f=55&t=211

 

When I ran it, I ran a 13.2 with 4.5 fuel pressure. I raised it to 6.5 and ran the 12.9. I didn't try for higher, I thought 6.5 was pushing limits. I do have a return line.

Another thing, the total timing is set at 34.

Fuel float bowl levels are right at the bottom of sight glass.

Through a couple of trial & error tunes and backfires through the carb, I replaced the power valve with a brand new one. This was all prior to the race track. I'll research that a bit more though.

 

are you referring to power valve NUMBERS or fuel pressure measured at the carb inlet port?
fuel pressure should not exceed 5 psi in most carb applications
if you want to lean it out youll want a lower numerical power valve, IE if your now getting richer as the throttle opens Id go back to a 4.5 power valve and slightly larger primary carb jets, keep in mind jets provide the base line ,power valves ADD fuel as the vacuum drops as air flow increases
btw Ive generally found you would be best served trying for about 13.7:1-14.2:1 fuel/air ratio at idle with a consistent and predictable but slow enrichment curve that gets you close to about 12.6:1 at wide open throttle above about 3500rpm, this tends to reduce plugs getting fouled[/color]

[/B]

POWER ENRICHMENT SYSTEM
The power enrichment system supplies additional fuel to the
main system during heavy load or full power situations. Holley
carburetors utilize a vacuum operated power enrichment system
and a selection of power valves is available to “time” this sys-
tem’s operation to your specific needs. Each Holley power
valve is stamped with a number to indicate the vacuum opening
point. For example, the number “65” indicates that the power
valve will open when the engine vacuum drops to 6.5" or
below. An accurate vacuum gauge, such as Holley P/N
26-501,
should be used when determining the correct power
valve to use. A
competition or race engine which has a long
duration high overlap camshaft will have low manifold vacuum
at idle speeds. If the vehicle has a manual transmission, take
the vacuum reading with the engine thoroughly warmed up and
at idle. If the vehicle is equipped with an automatic transmis-
sion, take the vacuum reading with the engine thoroughly
warmed up and idling in gear. In either case, the power valve
selected should be 1/2 the intake manifold vacuum reading
taken. EXAMPLE: 13” Hg vacuum reading divided by 2 = 6.5
power valve. If your reading divided by 2 lands on an even
number you should select the next lowest power valve. EXAM-
PLE: 8” Hg vacuum reading divided by 2 = 4 power valve.
Since there is no #4 power valve you should use a 3.5.
Most of the popular Holley “Street Legal” and “Street
Performance” carburetors incorporate a power valve blow-out
protection system. A special check valve is located in the throt-
tle body expressly for this purpose. This check valve is
designed to be normally open but will quickly seat to close off
the internal vacuum passage when a backfire occurs. Once
closed, the check valve interrupts the pressure wave caused by
the backfire, thus protecting the power valve.
If you have a carburetor older than 1992 (or you have experi-
enced an extreme backfire) and expect a blown power valve,
use this simple test. TEST: At idle turn your idle mixture screws
(found on the side of the metering block) all the way in. If your
engine dies the power valve is not blown

btw Ive generally found you would be best served trying for about 13.7:1-14.2:1 fuel/air ratio at idle with a consistent and predictable but slow enrichment curve that gets you close to about 12.6:1 at wide open throttle above about 3500rpm, this tends to reduce plugs getting fouled

 

You have 2 problems.
No power at wot. I don't know what cam you have but with those heads and the intake with any decent cam the motor should be making way more power then a 12.9et. afr at wot is fine and 34 degrees should be fine too. So there is something else wrong. Whats are you mph and 60 foot times? Are you sure tdc is correct on the balancer and tab?
As for the rich on acceleration, what is the afr when cruising on the highway?

 

http://m.summitracing.com/parts/hrs-180345-10

Cam is Howards Cam 180345-10, link above. It came with engine


1.6 roller rockers. 12.9 @ 106. 1.8 60' time. Cruising freeway at 70mph in overdrive 3000 rpms is the 12.5-13:1 range. I have 4.10 posi rearend.

I am for certain the balancer is correct.

As for fuel pressure, I mean 6.5 up from 4.5 at the gauge before carb inlet.

 

There is definitely something wrong at wot. According to your afr and timing it should at worst be close enough. I would double check tdc with a piston stop. If you are backfiring through the intake you are more than likely way more advanced than 34. With the setup you have it should be a beast at the track.
The light acceleration issue I would look into after the finding out what is causing it to be so down on power.

 

the backfire through the intake was before the track runs. That happened upon initial starting and trying to get the motor even running. I then replaced the power valve and Its now got about 1500 miles on it since then (April).

My 350 pulled harder above 5000 rpms than this motor does. My 406 is a beast off the line through 2nd then it just falls flat in 3rd gear above 5000rpms. I am 100% sure of TDC readings.

 

It sounds like you are running lean and upping the fuel pressure and running faster seems to go in that direction also. But according to you wideband you are right around where you should be.
Anyone else have any ideas?
Also with the rich acceleration, did you remove the powervalve and square jet it?

 

Afr should be closer to 12.5-12.9 at wot! Not at idle! If you are 10-11:1 under accel it needs carb tuning. I'd rejet.

However upping fuel pressure helped? Screw ET, what was the mph change? If mph also went up then you probably were lean and the wideband readings are false.

You have a low 11 second 117-120 mph engine combo

 

maybe i am reading it wrong, but I thought it was 12.5-12.9 at wot and rich under normal acceleration.
With that cam idle readings are probably reading false lean and useless. So if it is reading 12.5 at idle it's probably so rich you can't even stand near it.

 

I read that to but he said its 10-11 at touchin pedal which means normal accel but back to 12.9 when let off the gas?

I assume its rich at idle. I like leaner idle and more advance with cams that big

 

http://www.skipwhiteperformance.com/...x?Item=6500-CL

For what its worth, do you think this is holding me back? It was $45 brand new.

At all cruising speeds and at idle the AF gauge reads 12.5 - 12.9. Under any level of acceleration it goes rich. Sounds like im going to see what powe valve is in there. I can look tinight.

Also, I will look at my time slips tonight to get the exact mph readings per run.

 

What distributor are you running?

 

The one in the link on the post above yours.

 

no idea, looks like a regular old hei distributor. Not what I would use but I couldn't say if that is your problem. usually if its a weak spark it would break up up top.

 

Hows a distributor only cost 38$? I would verify its firing all cylinders and giving correct timing at the motor. Verify with a light

 

lol, yea a rebuilt from autozone is $99!

 

I have Quickfuel 6.5 power valve. http://www.quickfueltechnology.com/m...-assembly.html

 

run with 4.5 pounds of pressure at carb inlet:
R/T was .296
13.221 @ 104.27. 1.976 60' time

Run with 6.5 pounds of pressure at carb inlet:
R/T was .122
12.990 @ 106.40. 1.882 60' time

 

Recheck your wideband, and take a look at your plugs. If you can but it aint easy, put in a fresh spark plug in an easy to access cylinder, and quickly do a street wot pull thru 2nd gear to redline and immediately shut down motor in neutral and coast/brake to a stop. Pulled over, take out that plug and look at the fuel coloration. And look for a timing mark on the ground strap. That will verify your wideband.

I cant believe raising fuel pressure picked up power if its as rich as you say the wideband is reading

 

For $45 it's entirely likely that it's a piece of junk, module included. Perhaps it's dropping sparks randomly and the change in cylinder pressure from even mild accelertion is enough to snuff it out. It's been known to happen.
Just throwing it out there.

 

*****EDIT******
I think this thread is now more geared towards a "Carburetor" question. I began a new thread there titled Quick Fuel carb.

Today's results:

I came into today with vacuum in "Park" at about 12 inch but I was running rich throughout the whole rpm band.

So, I got rid of my "All-in-one" $45 distributor & purchased an MSD Pro-Billet distributor and an MSD Blaster coil

As we began to adjust mixture screws and set the timing, the focus this time was not to obtain most vacuum, rather it was to obtain the proper A/F mixture. Based on advice from a local speedshop, the numbers below reflect the appropriate mixtures:


AFR in park: 12.8 - 13.1
AFR in gear: 13.9 - 14.2
AFR at WOT: 12.9 - 13.1
Fuel Pressure: 5.0psi
Fuel bowl level: just below center site glass, as instructed on the Quickfuel Carburetor manual
Vacuum in Park: 8in
Vacuum in Gear: 4in
Initial timing: 12
Total timing: 34
All mixture screws are turned out about 1 full turn.
Power Valve is 6.5

I haven't gotten it on dyno to see results but it feels minimally stronger. Though I still think it has more in it. Any other suggestions?

This is the camshaft I have (with 1.6 rockers)
http://www.skipwhiteperformance.com/...Item=180345-10

 

See reply in your new thread
https://www.thirdgen.org/forums/carb...fuel-carb.html