I have what I suspect is a lean miss in my Z but figured I would ask and see what everyone thinks anyway.I have a 10:1 355 in my Z with a 750 DP Speed Demon,MSD HEI (with vacuum advance)and 6AL,Weiand Stealth dual plane,Comp Xtreme 274 cam.If I cruise at light throttle around 1,500 to 2,500,all is well..nice steady cruise..very nice,no probs.But if I bring it up slowly while cruising to 3,100 to around 3,600 (55 to 70 mph),she surges or misses quit steadily.No miss at idle (steady lope at 750rpm-10" vacuum) or high end,if I launch under hard throttle and run her up to 5,800 shift point,she goes like hell,no miss or bog,flat spot,none of that,just that cruise rpm she misses.Can this be too lean of primary jetting?I am running 70's right now and 75's secondary/.31 squirters both sides/stock 6.5 PV.I am leaning towards the lean surge but not totally sure.What are your thoughts on this??Thanks for any help guys,much appreciated.

 

My guess would be a flat spot in the secondary pump. The next time you drive, pay attention as to where exactly that flat spot is reletive to the throttle position. As in just as the secondaries start to open...just after..just before, etc. then go out with the car off and see what the pumps are going there.

I had a similar problem and it was a mis-adjusted secondary pump arm. Made a lean spot right in between the primary and secondary pumps.

Could also be the power valve opening at part throttle there...could run a vacuuum gauge into the car and see if the flat spot happens right as it passes 6.5".

 

Hi there. First thing is that vaccuum is a little low for 750RPM and that cam. My stroker makes 13" vacuum in gear @ 700RPM.

I would check the ignition curve first....after that check to see your total and then work your way over to the carb

Check the plugs after a hard run. They will tell you alot from looking at them.