Here's one for you. Not too uncommon I would think however I'm looking for opinions.
First the background. Engine specs and such are in my signature. Suffice it to say that I have maybe 400chp. That would be all in by 5500rpm depending on which computer model or chassis dyno graph you want to read.
Last years 3700lb chassis went 12.7@105.
This years chassis (which is the same weight of 3700lb, unfortunately) will be heading to the strip this weekend for some preliminary testing.
Here's the situation with results from testing on private property.
1st gear to 6000, no problem with WOT AFR's at 12.5.
2nd gear to 6000, also no problem with AFR's the same.
3rd approaching 5000 and the AFR's drop off until I lift well before 6k.
AFR's of 12.5 to 14 to 16...
Ideas?
Fuel system is: New tank with a replaced fuel pickup from EFI to carbed style. No filter sock.
New 110 GPH mechanical pump. New filter in original EFI location. All new 3/8th's steel line from tank to pump. Another new Russel filter between pump and carb. New -6 stainless throughout. Holley 670 vacuum secondary Street Avenger with tuning for MPG (15 -16 AFR at hiway speed) but still has original secondary diaghragm spring. Secondary jetting remains as stock (I think).
An interesting note. I had fuel delivery problems even more severe than this example (wouldn't pull from 55mph to 80mph without starving) however I found that the primary float was 'crushed and more or less stuck' and as such the float levels were way off with the bowl running dry on demand.
This problem, although similar, should be unrelated.

 

Pumps don't do a very good job of sucking fuel through a fine filter. That's why there's a screen before the pump to stop the birds and rocks, and a fine filter after the pump to get out the small stuff that would hurt the carb.

Either put a sock back on, bypass the EFI filter, and keep the fine in-line filter after the pump; or get a less fine filter in place of the EFI filter and keep the fine in-line filter after the pump.

 

Yup; you can't put a restriction, even a not-too-severe one like that filter you have, on the suction side of the pump.

Put the sock back. Put the filter between the pump and the carb. on the "push" side, where the pump can successfully force fuel through it.

 

Interesting. I hadn't considered how restrictive the EFI filter might be.
Considering what a pain it is to drop the tank and access the pickup, I'll try the bypass idea for now (simple enough). I couldn't find the correct carb style filter sock prior to installing the tank earlier this year so I chose to go without.
Thanks for that. I'll report back once I've had a chance to retest.

 

Thought I'd report back finally seeing as I never did.
I found the problem a while back.
Fuel pump lobe gone.
Lesson learned....even with a roller cam, there's still a need for oil additives. And a bronze or ceramic or roller tipped fuel pump push rod.