I just bought a race demon 825, (i know why a demon) but i got it for a great price, anyway seems to run well but when you stuff it there is a slight hesitation, anyone have any advise on tuning these, I ordered the book, but wont be in until later this week........also it has stock jetting, 4.5 powevalve, (6.5 is stock) what affect will that have when matting it? if any?
it's on a zz 502. as you can tell, I am a rookie
with carbs............

Hey, don't listen to any Demon bashing. I have a vacuum secondary on my "502" and I am very happy with its performance and ease of tuning for me as a rookie too! I am not a carbuerator guy but it sounds to me like the squirter has too much slack or too slow of a cam. I trust that your post will get much better analysis than I can but the carbuerator is good.

I would think the ZZ502 would pull a fair amount of vacume considering it's a crate motor so the 4.5 power valve is to low I bet. Take a vacume reading at cruize speed and select your power valve 1 or 2 inches below that. Your accelerator pump timing and shot size and duration will also effect the way it responds. Usually a 4.5 powervalve would be used on an engine with like 8 inches of vacume at idle, I'm sure your zz is way higher than that.

I purchased a speed demon 850 a few years back and it has been on several engines since then it has worked great the only mod I had to do was downsize the air bleed holes on the top of the carb that took care of the off idle hesitation .
This carb has been used on a 428 FE ford 427 FE ford a 355 sb chevy and a 406 roller motor . this carb has out performed all the carbs previously used on these engines at the drag strip and on the dyno :D

I have a race demon on a 502 also. First things first: which sleeve do you have? If its black change it to blue. Where are your idle mixture screws set, start at one out, do not bottom them out otherwise you'll destroy the O-ring, slowly turn them out, gently, then out 1 turn. Leave the idle bleed screws alone. It may be worth wile to make sure the butterflies are set properly, that involves taking the carb off and adjusting the butterflies so that .020" of transfer slot is showing. Do one thing at a time. Another factor is the main jets: mine came with 78's and I changed them to 73's. Good luck and make sure you have at least 20 degrees of initial timing set otherwise it won't run worth a crap.