At a loss - engine stalls under load

[Tinkerr]

Is the tank venting properly? If not, could be creating a vacuum situation with the fuel system after a few hard pulls. As a side note you have a solid lifter BB pulling 17" of vacuum at idle? Factory were at PV's were 6.5 on solid lifter BB's. Idle vacuum divided by 2 is the formula for PV.

[David K]

Go back to the last thing you changed…see what happens.

[R68GTO]

Thanks for all the input guys.  The engine pulls 14.5" of vacuum t 900 rpm idle.  I'll try to crack the gas cap on the tank to eliminate that potential cause.  Per suggestion, I'll pull the carb again and check my PV installation.  Will also make sure everything else on the carb looks ok.
Is there any possibility that I have an intermittent short in the electrical circuit between the ignition and the coil?  I dunno....if it was that, it would not just do it under harder access correct?  Totally grasping at straws these days.

[janobyte]

Just throwing it out there: have somebody ride behind you to see what, if any, color smoke out the exhaust. When it dies, don't try to start, pull and read the plugs,,lean vs. rich condition. Does it die or fall on it's face pulling a holeshot?

Normal operating temp?

[R68GTO]

Car runs cool.....roughly 180 degrees.  I'll pull the plugs and take a look, might just change them to eliminate that potential cause though I would think if I had a plug issue, it would run rough all the time.

[David K]

Did the problem occur out of the blue?

I have been trying to recall the sequence of events.  I believe this condition started after I installed new 8.5 power valves in the carb.  I did check them before installing.
[/quote
Go backwards to fix what started this problem.

[janobyte]

Checking plugs to see if you have a rich or lean condition asap after the issue.

[KurtS]

It doesn't sound electrical / spark, sounds more fuel related.
Do you have a spare carb laying around to try? I'd also ask Erik, he is good at troubleshooting.

[R68GTO]

Update....borrowed a carb from my brother and swapped it onto the car.  Good news......stall condition under load is gone.  Bad news, I have almost no vacuum (5 inches) and the engine has a slight miss in it.  I adjusted the idle mixture to try to bring the vacuum up with no luck. 
One of the other things I noticed is that the new carb puts my car in fast idle when cold, my old carb never did that.  Could that be an indicator of the cause of my past problem?
Going to go back through my wires and plugs, adjust timing, etc. to see if I can find the source of the miss. Feel like I'm headed in the right direction, just not there yet.
Thanks again for all the ideas!
Jim

[David K]

So the carb is the problem. The carb is supposed to be at fast idle when engine is cold, and idles down as it warms up. Is the borrowed car close to your carb specs?

[R68GTO]

Carb is essentially the same, just a newer version

[R68GTO]

Did more testing tonight.  Set initial timing at 4 degrees BTDC, adjusted idle mixture screws (2 turns out) and set the idle at 1000 rpm.  Seems to run pretty good with no cutout or stalling under hard acceleration.  But just have 5 inches of vacuum?  What about a carb change takes me from 14.5 inches of vacuum to 5?  Nothing I tried seemed to bring the vacuum up other than rpm.  pulled about 12 inches at 2,000 rpm

[cook_dw]

Is fuel coming out of the boosters at idle?

[R68GTO]

Need some help understanding the question…..fuel spraying out at normal idle looking down into the primaries?

[cook_dw]

Yes is there any fuel (at idle) coming out (spraying, dripping etc) of the boosters of the carb?  There shouldn't be at idle.  Idle circuit of the carb is below the primary throttle plates so if you see fuel on top of the plates or dripping from the boosters you have a power valve failure or sized incorrectly.  Did you ever measure your idle vacuum when you first got the car running?  Assuming you have a stock L78/L72 cam then you should be around 16-20"hg.  I'm making a few assumptions as I know Eric would set this up correctly.  Have you not reached out to him on your issues?