dandd

First I'm new to the list, been perusing the carb form for a while trying to bug my issues.
Here's what I have:
2002 5.3 ~100k
new 4l65e
Compression 160-180
Texas Speed 220/220 with .590 lift LSA112
msd 6010
Holley PART# 0-76650BK 650 ultra Double pumper
pri/sec 63/68
nozzle 28/31
accel cam blue
6.5 fuel pressure
transition slot ~.015 at idle
~13 AFR at idle
Now the issues, it idles great but there is a huge lean bog issues at 12-20% (~study state) throttle the AFR goes to ~17+ almost undriveable.
steady 60mph (~14 aAFR) roll into the gas a little and the same thing happens huge lean bog.

I tried bigger jets same issues just runs richer
I tried 31, 32, 35 same issues

Also during the lean bog there is pinging

This is with the MSD pill #1
Also tried custom profile with reduced timing at idle (~17 12+5 vac) (max ~38 33+5)

It seems everything I do yields roughly the same results
I hoping someone with a similar setup can help me out or give me a direction to go.

Thanks

Pop N Wood

iTrader: (1)

Check float levels and fuel pressure. Also make sure none of the air bleeds or other orifices are blocked and no gasket leaks.

You have the ulta DP so your idle feed restrictors are replaceable. Go a couple of sizes larger on those. You might want to go a step smaller on the idle air bleeds as well. Set the IFR to get the right cruise AFR just off idle than tweak the bleeds to keep the AFR flat until the main circuits take over. The main jets do have an affect on the transition circuits so you really should tune them at WOT first.

Set the accel pump circuit last after all the steady throttle AFR's are where you want them.

dandd

Float level in the sight glass is 1/2 way and the fuel pressure is 6.5-7. I'll thick I'll have to tear it down to go through all the orifices and gaskets.
One odd thing is that after engine shutdown the fuel remains ~1/2 of the sight glass in the secondary but the pri. drops to were you don't see it. Also a restart after 3-5 minuites you have to floor it to restart as if flooded.

This Holley model does not have adjustable ifr's so I did replace the primary meter with a quick fuel It had size 33 ifr so i drilled some blanks to ~38. This caused a rich condition at cruise with slight improvement to the bog/stutter.

With that said, for the increase in the ifr wouldn't the idle air have to increase the same % to maintain the fuel ratio? The bad thing is this carb does not have adjustable idle air's

Doug G

Sounds more like the squirter size is too small or maybe the pump shot ?
I would also look into your power valve and also the gasket (for the fuel level drop)
Jets only effect cruise and wot (or anything between)
Normally a dead rich condition happens as you loose velocity of the air flow and the vacuum it creates.

Pop N Wood

iTrader: (1)

Sounds like you need to find the leak in the primary. That pretty much has to be a gasket or a crack of some type. I initially thought power valve leaking but that would just fill up the main well, shouldn't leave the carb. Leaky accel pump would leave a puddle outside the manifold, not sure it could go down the throat.

Check for vacuum leaks as well.

This is why tuning advice is so difficult to give. There are 100 details that need to be checked before swapping orifices is productive.

G Atsma

And why injection has taken over from carbs.

Pop N Wood

iTrader: (1)

LOL, too funny

Doug G

Personally....I like to tinker, so a carb is fun for me guess I'm weird like that ?

dandd

OK, I'm back.

Got a new carb 680 cfm ss quick fuel with vacuum secondaries. I went with this due to the adjustability of the IFR, power valve restrictors and adjustable bleeders.

After install the same issues persist with the lean tip-in in the 1400-2000 rmp range.

My thought was to extent the idle transition fuel futher up the rpm range. So here's what I did.

installed .025 IFR (originally .031) and .048 IAB (originally .070)

With this combo I'm seeing almost no tip-in lean stumble and a AFR of around 13-15 without the power value opening.

Do you believe this is the correct approch to resolve the lean tip-in issue?

My other question is there a way to determine the correct IFR size or is it based on the relationship in size on the IAB?

Also what is the difference between maintaining the the IAB size and increasing the IFR
or
maintaining the IFR size and decreasing the IAB's

Pop N Wood

iTrader: (1)

I guess I missed the part about the lean tip in occurring at 1400 RPM.

The IFR meters the amount of fuel being sucked in by the airflow through the carb, but without an air bleed the AFR would get progressively richer as the airflow increased. My approach is to set the restrictor to get the AFR right at the low RPM than adjust the bleed so the AFR stays constant up to the RPM where the main circuits take over. The transition and main circuits work the same way, just different bleeds, RPM band and the jets vs. IFR.

So yeah, your AFR was right at just off idle RPM but needed to be fattened up at the higher RPM’s in the transition band, so smaller bleed fixes that. By 2200 RPM you are pretty much on the main circuits. Changing IFR and bleeds in pairs is a good approach. If you made your IFR smaller now it would lean out your cruise AFR a tad.

I typically adjust the bleeds/IFR with slow throttle movements and once I get the AFR to stay flat through out the band move on to the accel pump shot. Originally I had a huge accel pump and squirter. That masked any bog with WOT, but cruising with slight throttle movements the car had this annoying hesitation from fluctuating AFR's. Getting the transition circuits right got rid of that and let me go down several sizes on the accell pump shot.

Also remember the main jets affect both the idle and transition circuits, so set them first.

By the way, it is pretty easy to drill out pressed in IFR’s and bleeds and replace them with brass set screws that you drill to size. Much cheaper than buying a box o jets too. But that is a nice carb, no worries there.

dandd

So, I'm down to where it's a little rich at idle (arf 12). Would it be best to reduce by IFR to 23 and leave the IAB 47. I believe this would retain the strong vacuum 2k rpm's.

The other method would be to increase the IAB to get a leaner idle but I'm concerned that this reduce vacuum and not have as much fuel at 2k rpm's


???

Pop N Wood

iTrader: (1)

Not sure what you are asking. Idle mixture is set with the idle mixture screws. The IFR's are for cruising at say 1200 RPM. Typically want a 14 or more cruise and let the power valve richen it up with throttle movement.

speedtigger

iTrader: (16)

The idle screws on the outside of the metering block should be able to adjust your idle AFR. Is the car not responding to adjustment of those screws?

pantera_efi

iTrader: (1)

Hi Dan you need to enlarge/increase your Transfer Slots in the Throttle Blade AREA.

The method is the remove the throttle plate/machine that area.

The "tip" is the observation of the Blade Position when on the throttle stop ?

I have modified many carbies by ADDING Transfer Holes.

STATE your mixture screw setting.
THIS will tell me your Idle FUEL requirement.
MORE the ONE TURN AND you will require a increase, a simple Metering Block passage way drilling.

You may also need a Idle Fuel Air Bleed DECREASE in bore.

Lance

dandd

First, Thanks for all the advise it's been a great help.
juck yard 5.3 with Texas Speed 220/220 .590 lift lsa 112 cam and srings
current set is is:
ss 680 quick fuel with VS
IFR .025 (all 4)
IAB .049 (all 4)
HSAB .028 (all 4 original size)
mains 66
secondary 74
power valve 8.5 (power valve restrictors stock ~.052)
Vacuum at idle in drive 16"
idle screws 1/2 turn out
The result is a AFR of 13 at idle. All tip-in is gone. Freeway and light throttle cruise is ~14 ARF. Hard acceleration is ~11-12 ARF this is occurring when the vacuum is below the power valve threshold.
So I think I;m past the hump and am getting down to finer tuning in which I'll start with the power valve resistors and drop them down to .049 (~10% area)
The old nova is a blast to drive now with crisp responce and no more lean tip-in.

Pop N Wood

iTrader: (1)

Man, sounds like a blast.

You are a bit rich, some MPG's to be gained, but who cares as long as the throttles response is good?