Carbureted LSX forum - Popping off the line?

Not new to this site just a new screen name,(couldnt remember password).
The problem is, it pops(goes lean and backfires) at about 4300rpm in first gear and i leave at about 3200 and then just picks up and runs 12.3/12.5 on widebands all the way thru 7000 rpm in both of the other gears with no pop. I thought it was the fuel sloshing from vents into the venturi but i put a hose from vent to vent and vented the middle of hose like the railcars do. I do have a stock hood on it and was told by a ten five friend of mine that REHER-MORRISON told him that any n/a engine needed at least 4 open inches above the the body of carb, i dont know if any one has heard of this issue or has had it before but its slowing me down almost a full second and i wanna hit the 11's before i spray this thing. So all in all PLEASE HELP?!?!?!?!?!
The set up is as follows:
2000 Z-28 10 pt cage, full interior minus speakers and ac, subframes, 7.5 10 bolt mini spooled 4.10 gears
383 stroker-eagle crank and rods, wiseco -8cc dished pistons
243 heads-total milled 52 thousandths, 2.02/1.575 valves, p&p'd, prc gold springs and titanium retainers
camshaft-571/573 lift, 240/240 duration, 112 lsa
stock rockers
hardened 7.350 pushrods
1-3/4 headers with turn downs for wide bands
victor jr carb intake
holley 4150 street hp 950cfm mechanical sec. 86ft/87rr w/pv plugs
msd 6ls box
timing- 24*@0 ramped to 33*@1500rpm, 33* all the way to 6000rpm then ramped to 35*@7500
redline at 7000rpm
spark plugs- ac delco stock style iridium @35
transmission-th400 automatic(nothing special just a shift kit)
weight- guesstimate 3600?
R/T: .006
60 FT: 1.71
1/8 ET: 7.79
1/8 MPH: 90.34
1/4 ET: 12.11
1/4 MPH: 113.24

Could it be happening when the secondaries open? Maybe the accel pump shot is insufficient or you need to switch to a different secondary cam?

Try disconnecting the secondary linkage temporarily and see if things clear up.

Ok i will give that a try tonight, and post back. I hope that fixes it, this car has given me crap for the last 7 years, i think its jinxed.

Check for wot. I had a similar problem. Pucked up 1.3sec next time at the track with Wot.

Well its not the wide open problem and not the secondaries or timing or fuel jets. So i am going to the track tonight to test n tune, i installed the jet extensions and notched floats and also installed lakewood rear drag shocks to help with the rear end squat. Also i am trying this new ls30 joe gibbs oil so post your feed back if you have tried it and ill post up results for tonight and opinion about oil.

Well didn't change oil yet, front jet extensions bad idea, back jet extensions good idea, rear shocks a full tenth off 60 ft time, moved regulator from back of car to front of car next to carb like its suppose to be and cut fuel psi from 11.5psi to 6.5psi like it should be and still could not get rid of pop or break into the 11's. What gives?

Also pulled hood off and installed air cleaner no difference at all not even the weight helped out.

No ideas?

Well, wish I saw you install jet extensions in the front, lol.

You watch the wide band? It goes lean at the time of incident? Probably hard to tell, but if you know anyone with spare carb, try it out if they don't mind.

Sounds like you have any suggestions I was going to make covered. Fuel pressure in excess will do that but you fixed it, fuel slosh from the rear W/O jet extensions will do so, so you have me thinking the carb is clearly probably the issue, check the power valve just in case, but that usually only effects idle.

Yea it happens at time of incident and reads 15.3 on WB.

Also it does it before the 60ft