engine cuts out but only in first under hard acceleration,

[Grumpy]

Pretty specific conditions, right?
I was messing around the other night, and went full throttle from a dead stop. This car has never been a terror off the line, and will really only bark the tires if I plant it from a dead stop. Engine really doesn't come alive until 3000-3500 rpm. So it did its normal lazy takeoff, but when I hit about 4k in first, it really fell flat on its face. I shifted to second, and it picked right back up, and pulled strong through 6200 where my shift light comes on. Third felt strong as well.
Tried another pull, but walked it up to about 3k in first before matting it, and it pulled well all the way up in first and second.
Combo is 10.5:1 350 Chevy, Comp XR294HR cam, performer rpm air gap intake, performer rpm heads, holley 750 street hp vacuum secondary. Yes, the carb is a tad big, but it's what holley recommended with my setup due to 6500 max rpm. It's stock apart from a 4.5 power valve, since I'm only making 9" of vacuum at idle. Th350 trans, 2400 stall, 3.70 gear.
I suspect a vacuum secondary issue, but I'm all ears. It's odd that it only does this in first gear. I can walk mid-12 second cars from a roll, but can't beat a low-13 second car from a dig because of how lazy it is down low. My impression is it's lazy down low due to the combo and there's not much I can do about that with current parts, but the falling flat thing has me stumped.
I'm really thinking about putting the Sniper EFI on it this winter.......

when your trying to isolate and test any issue it helps to mentally step back and ask yourself ,
"what condition has changed or been induced that might explain this"
then test your theory...THINK LOGICALLY NEVER ASSUME!
Id start by installing a fuel pressure gauge sensor for the remote dash mount fuel pressure gauge at the carb inlet port and having someone watch it carefully as you made a few hard acceleration runs,
YOU WANT A SOLID CONSISTENT 5 PSI FUEL PRESSURE ,
as a start point at the carb INLET PORT,
having an under the hood fuel pressure gauge may be helpful,
but its useless for diagnosing several issues that an accurate,
dash mounted fuel pressure gauge will be helpful for.
have you adjusted both the fuel bowl fuel levels so the idling engine shows fuel just level with the sight plugs lower edge.
meassure your plenum vacuum at about 1000 rpm idle, and install a power valve thats rated at near 1/2, ie if your vacuum reads 9" then youll need a 4.5 power valve as a STARTING POINT to tuning, you may need one step richer or leaner.
it should be obvious that you may need to be making jet changes, power valve and accelerator pump cam changes, take accurate notes and document changes and the results you get from the changes.

now it may be something else but Id suspect that either the fuel pump has a hard time over coming the initial inertial loads that are reduced once the cars launched, the sudden increase in inertial load on the fuel pump might stall some electric fuel pumps for a couple seconds , or it may be a problem with the carbs acceleration fuel pump not covering the fuel demands , allowing a momentary lean-out in the fuel/air ratio.
http://garage.grumpysperformance.com/index.php?threads/holley-accelerator-pumps-cams.1790/
swapping to a BLUE Holley Accelerator Pump Cam, (and maybe a 50 cc accelerator pump vs a stock 35 cc pump) might help

or the oil pan contents sloshing to the rear uncover the pick-up and your oil pressure sensor is cutting electric to the fuel pump or ignition, until the oil pressure returns
Id sure throw an extra quart of oil in the engine and install a fuel pressure gauge to isolate those two potential sources before looking further
its simply a process of isolate and test until you locate the problems source, just never assume, test.
btw a carburetor inlet port mount fuel gauge alone, without a remote sensor and dash mount fuel gauge does little good,
simply because you can,t see whats going on while the cars accelerating under load.
I'm sure we can locate the source of your problem , but it will take some time and testing to do so as usual,
I'd certainly think its either a fuel delivery or an electrical/ignition related issue ,or a loose electrical connection or defective sensor,
simply based on the brief and intermittent
symptom's and Id check for loose battery cable connections and loose electrical grounds

most guys have little real experience at isolate and test procedures and many can,t use test equipment or even fully understand what to look for.
DON,T PAY FOR IT ...DO IT YOURSELF!!!
IT WILL COST LESS EVEN AFTER PAYING FOR THE TOOLS, than paying for it AT MOST GARAGES.
A compression test,ALONE, IS NOT A LEAK DOWN TEST, a LEAK DOWN TEST WILL GIVE YOU THE COMPRESSION TEST INFO, ALONG WITH OTHER INFO

you'll find that you'll gain basic skills, own new tools and PAY LESS MONEY

http://en.wikipedia.org/wiki/Leak-down_tester

http://www.carcraft.com/techarticles/11 ... index.html

BEFORE YOU GET INVOLVED WITH TESTING , YOUR ENGINE,READ THRU THESE THREADS, AND LINKS AS THEY WILL HELP ISOLATE THE PROBLEM, and THEY HAVE A GOOD DEAL OF USEFUL INFO
you really need

http://www.testequipmentdepot.com/e...1100200223789&utm_content=All Extech Products
INFRARED TEMP GUN

a timing light,

http://www.harborfreight.com/3-1-2-half ... 95670.html
multi meter,

vacuum gauge,

fuel pressure gauge

http://www.harborfreight.com/cylinder-l ... 94190.html

HARBOR FREIGHT, UNDER $40

http://buy1.snapon.com/products/diagnos ... pv309a.asp

SNAP ON $330

http://www.summitracing.com/parts/SUM-900010/

http://www.summitracing.com/parts/OTC-5609/

SUMMIT $80-$100
compression test /leak down tester

dial indicator with stand

and a degree wheel

damper tool

and a shop manual
and more related reference material
certainly won,t hurt

http://garage.grumpysperformance.com/index.php?threads/verifying-your-real-advance-curve.4683/

http://garage.grumpysperformance.com/index.php?threads/bare-minimum-tools.11026/#post-48779

http://garage.grumpysperformance.com/index.php?threads/no-computer-now-what.13973/#post-71209