Hello I am a new to this web site I have researched all threads on holley carbs found nothing similar to my problem. I have a 1974 nova 350 ran fine prior to intake and carb change. I installed a holley street dom intake p/n 300-38 and mounted a used but professionally rebuilt holley carb 600 cfm p/n 0-80457-2. Fuel line is intact, vacuum line from stock points distributor to carb and carb to pcv hooked up all other vac line on carb are plugged and electric choke is working. Fires up and idles great. Once warmed up it stumbles when you gas it and stumbles at 50-60 mph. I thought that I would have gained power but it seems I have loss alot of power since the conversion. Appreciate any suggestions

Each carb must be set up to the package it is installed on.

Adjust pump shooter levers so they don't bind at full throttle.
Adjust floats by removing the sight plugs. Gas level should be just below the sight plugs.
Adjust idle mixture screws. Attach vacuum gage. Turn idle screw in until vacuum drops. Turn idle screw out until max vacuum is achieved. Do other side.
Change power valve size to 1/2 of vacuum.
If car stumbles increase shooter size. If car bogs decrease shooter size. If stumble or bog is one second long or more. Increase by 3 sizes.
Change or clean plugs. Drive car. Remove plugs and increase jet size if plugs are white or grey. Decrease jet size if plugs are black or dark brown. Proper plug color should be the color of dirt.

Ok checked float level and changed vacuum line (distributor to largest vac port on carb 3/8) got rid of the pcv hook up. The shooters adjustment is all greek to me. Test drove and had an improvement seems to have more power than before but maybe my terminology is wrong when I said stumble it is a short hesitation when I hit the gas at the start, then at 60 mph (every time at 60mph starts popping and you can feel a loss of power or a hesitation. With this new set up( new carb and intake) it seems I loss that tire burning take off but got faster speed by 20 mph increase, is that the results or can I adjust something?

the accelerator pump arm ? is the linkage pressing on the accel pump lever? also when the throottle is WOt is there should still be some travel left in the arm? if its binding or constantly pressed the linkage tab thing will need to be rebent.

tabby need bendy

I had almost the same problem once,i had to changed the power valve,jets and add a spacer plate to solve my problem, all engines are different so good luck,,
Robbie

Thanks bhoys for the info came out to be a timing problem..I sure appreciate it