AF lean out on 2-3 change

[Chargermal]

Looking for confirmation that I have a fuel supply issue, which is why my AFs are going lean.

Motor is a 480hp 6.1 G3 Hemi running dual Edelbrock quads. Hi flo needles/seats. Trans is a manualised 3 speed Torqueflite.

Fuel system is a Carter 110GPH ELECTRIC, 3/8 line from tank to pump, 1/2” line from pump to reg and reg to carbs. Pressure set at 7 PSI.

AFs at WOT show 12.7 rock steady thru 1st and 2nd gear....but they blow out to 13.4-13.6 on the 2-3 change and stays there while in 3rd.

I did four runs...first time I didnt ring it out in 1st and it went to 13.2 in top. 2nd, 3rd an 4th run were full blast - and I saw 13.4, 13.6 and 13.2on the 2-3 change....AFs at the top of 2nd were all 12.7.

This was with my cold air base, no filter but contoured air bells.

[gridslammer]

i would think what you are seeing is the load on the engine in each gear maybe possible over revv in first? fuel supply demand would be greater at the end of the run in high gear where the is a greater load on engine.

[Chargermal]

The change from 12.7 at peak rpm in 2 to 13.4 when changing into 3 shows an increase in demand...so that confirms what I was thinking.

[Racer71]

Need 1/2” from tank to pump for starters 3/8 to carbs and regulator would be ok or you could stick with your 1/2” you’re killing your pump with your current setup

[blown265]

G'day Mal

I like the Carter pumps and have used them for many years.
However, while the Carter 110gph is plenty for 500hp steady state (dyno), in the car and on the track, it can fall short on the power required to push the fuel weight against the acceleration of the car. I had the same problem with a good 383 Challenger, and cured it with a second pump in parallel with a return style reg. It didn't need the volume, but did need the delivery power to push forward. The AFRs levelled out through all gears. (instead of leaning out in the last 660feet)

Definately change the 3/8 prepump feed, but also consider a second pump.

Regards
Paul

[Caprimaniac]

Agree with rhe above- re- plumb. Others know more on thesenpumps then me.

As with EFI, you tune the furl table in 4. gear or where tou have tje highest loads. Doing so you go a little fat in 1.-3.. I assume if you jet the carb for 12.5 in 3., uou will seenit gets a little fat in 1.-2.

However, it might like 13.5?

[steve cowan]

I agree about larger inside diameter fuel line.
Would be interesting to jet the engine to achieve best MPH at the track,AFR might not be where we think it should be .

[Dan Timberlake]

A fuel pressure gage securely taped to the outside of the windshield plumbed right at the carb fuel inlets might be a revealing first step.

Also a fuel delivery test with the discharge/catch bucket 16 feet in the air ( ~ 5 psi hydrostatic head using 3/8" fuel line.

[Chargermal]

Thanks all. I’ll conduct a fuel pressure test as suggested.

I think I’ll see the pressure drop off...so will need to think on what approach to take - space is very limited unfo.

[Racer71]

Pressure doesn’t always equal volume but you would most likely see a drop at higher load. With that restrictive of an inlet the pump is probably rather noisy and it has to be cavitating pretty badly. A -10 or -12 into pump and a -6 feed to engine should be sufficient. Possibly a 2 or 4 micron filter plumbed in before pump would be good as well.

[MadBill]

2-4 microns is way too fine for a carb filter, especially upstream of the pump. 100 would be more like it, with perhaps a 40 micron one downstream.
A dash 12 line is 3/4" ID -for an under 500 hp engine? #8 in and a #6 or #8 out would be plenty. That pump comes with 3/8" NPT fittings, just over 1/2" ID.

BTW, Edelbrock recommends a 5.5 psi setting and a minimum of 2 psi at red-line WOT for their carbs: https://www.jegs.com/InstallationInstru ... 0-1406.pdf

[MadBill]

...
This was with my cold air base, no filter but contoured air bells.

If you don't find a fuel pressure issue, air turbulence might be affecting carb metering at high speed. You might try some kind of baffling around the carb inlets.

[Racer71]

Yea I as a bit fine on filter recommendations but I’m used to my alky efi stuff lol.

[MadBill]

Yea I as a bit fine on filter recommendations but I’m used to my alky efi stuff lol.

Ah, that would explain the line sizing and filter mesh differences!

[Rick!]

Float Levels checked?
Secondaries opening all the way?
You're engine doesn't need all the air the carbs can give it so it's probably not sucking hard enough to open the secondaries up. They are calibrated for a 600-750cfm demand and your engine is probably not generating 700CFM at 7000rpm even if it was at 100% VE (which it's not). Split that "suck" between two carbs and the secondary air valves may be just barely opening. Maybe change the angle of the air valve blade to be a little steeper and see what happens.
Best get the fundamentals out of the way before diving down the wrong rabbit hole.

The g-load on the fuel in the fuel line in 3rd gear is pretty small so the "backpressure" is on the order of a few tenths of a psi, even using the 1/2" fuel line. Edelbrock recommends 6.5psi fuel pressure so your reported 7psi should be adequate, if verified on the track.

After all that, report back. Seeing a richer 3rd gear WOT will certainly make you feel better but MPH on the time slip will tell you how the engine feels about it.