What is the vacuum issue?

Even when the carb works really well, this engine does have an off idle stumble. Most of us (who don't want to modify the intake manifold log) correct it by bumping up the timing and running a little better gas.

 

well on my 200 i have a pretty aggressive cam oversized vavles roller rockers dual roller timing chain pacemaker dual out headers and i had the head milled along with the 500cfm holley and aside from cooling issues it runs pretty good but since weve only had the carb on it a lil while we still are fine tuning it but yes for a stock application i wouldnt go above a 350cfm carb but i have more performance parts thatn a stock motor so i need the extra fuel

and right now i think i would be able to beat a lightly modded 289 in the quarter and be pretty close to a stock 5.0 fox body stang

 

I wasn't arguing with your set up, I was just saying I thought a 500 cfm carb on a stock I6 would be way overkill and 350 was probably pushing it. This was in response to 65andonly18's last post. A guy at work, who has done restoration and modification work on many different cars professionally, recently helped a friend modify a 302 in a Mustang. They installed a 600 cfm carb but with a more agressive cam among other mods.

 

no i wasnt arguing with u i was just describing my setup so the rest could see it too cause i agree with u a 500cfm on a stock 200 is way over kill and a 500cfm carb on my setup is a little overboard but a 350 would be too small in my opinion and im also planning to do more modifications in the near future so the 500cfm will be needed in the future and im a cheap bastard and wouldnt like having to buy another carb if i didnt need to