1980 Vette ,ZZ4 motor( 2500 miles )  3.55 rear , headers,  2 1/2 dual exhaust . holley 750 vac secondaries . 

It seams like it miss fires when I hit it and the rpm and power climb , I hear it in the exhaust and feel it , it does seam to get past it and builds power and rpm . So it is not a stumble it is more like a miss fire , I am sure there is power loss but it feels slight meaning the car is not hesitating or bucking it powers through it. 

To me it seams to happen when the 4 barrels are all opening , it is a new holley (750 vac ) I set it up with a vac gauge and on initial install i had 12 or 13 inches of vac , after i worked on mixture screws an now  I got a solid 17 inches of vac. 

Car idles perfect  , starts perfect , runs smooth , cool , and for the most part is tip top ! 

So any ideas where I can go searching for this apparent miss firing ? My gut tells me the carb is leaning out or that when the back 2 begin to open I am not rich enough and am fuel starved and I should have bought the 750 double pumper not the single pump vac secondaries .. 

Or not ...lol 

 

Barry

 

here is something . . .  If i mash peddle into carpet no issue at all ,, BUT lets say I am in manual 2 and i run motor up evenly with out punching it , , it is there i feel and here it breaking up but the minute i mash gas all good.  

I just pulled 3 random plugs all clean enough to re-box and return to part store , gap was a tiny bit tight so i adjusted it and will do the remaining 5 later . 

Is it possible this vac secondary is not opening when it should and I am leaning out the motor causing this issue cause a mis fire may be to strong a word to use it is more a poping sound in exhaust, 

Here is what i did , When I did the headers I changed plugs because I broke one , I never gaped them figuring they would be pre-set and close enough , I just did 6 of the 8 and all where tight I would say 35 and I set them to 45 as called for , I drove the car and it did not do it. I ran first and second to rpm limit with out opening all 4 barrels and no popping or stuttering, so in the am i am gonna do 7 and 8 plugs to finish it up.

Now why that made a difference I have no idea , every plug I did pull and re-gap was perfect I could have put them back in a box and returned them . So is the gap that critical I never would have thought so and I am hoping that I am fixed and not just lucky that the last ride was a fluke.

Not sure though if you were already at a .035 gap, that this would have caused the problem, but I guess anything is possible. Maybe in combination with the heat range of the plug...

My guess would have been a low end fuel issue from your description.

Good luck.

Paul

So I decided lets check the ignition , now after I re gaped the plugs and it appeared to correct the issue I also started to search Google .  What I think I have learned is a small gap can lead to un-burned fuel and that the bigger 45 gap provides a much hotter and bigger spark ensuring all the fuel is lit off. So if that is right what I herd or called a mis-fire may have been un-burnt fuel going off in the exhaust system making it sound like a misfire.

Let me end by saying that's what I gleaned from reading a dozen or more pages on line.  And if the issue is not resolved I will post back .....