Went to demons web site after I bought the speed demon 750 for my 355 because cam has more than 242 degrees duration to it. I can't seem to get the motor to idle correctly. I did the warm up and fuel bowls, and adjusted the air mixture. What else can I do.

Are you running ported or full-time vacuum advance?

hei distrib w vac adv and hyfireVI ignition

Yes, but where is your vacuum advance connected?

vac is attatched to the bottom port of carb

but which bottom port on the carb? the front is timed vacuum and the rear is ported (manifold) vacuum

Timed vaccume port sorry was sure what you were trying to get at.

You probably need to swap power valves, what power valve is in it now and how much vacuum are you pulling at idle?

vaccum on the gauge is at idle 16 has big cam and doesn't pull much vaccum

Not that big if you've got 16" at idle.

Sounds like you have plenty of Vac at 16 in.

Try this ******* trick.

At idle pull off a vacume hose to create a leak induce morte air to the misture. If the engine runs better then the idle mixture is too rich.

At idle put your hand over the card like a choke reduce air into the mixture. If the engine idles better then it is too lean.

You can adjust the mistures screws using this method in a pinch.

You can also set you mistue by the gage turn one screw until vac is maxmized then turn the other until max vacume.

Is the timing set too low? / Where are the throttle blades in relation to the idle transfer slots?

I had a hell of a time getting my Demon to idle rich. Turns out I had to drill out the idle air bleeds, still not perfect but it made a world of difference. The transfer slots are squared, all 4 mixture screws are just slightly more than 1 turn out and the air bleeds were drilled out to .073 16* initial timing no vacuum advance, idle at 750RPM in gear.

OMG
Called comp cams and timed engine to there specs 10* BTDC and was able to adjust carb and timing on engine. The motor makes great power in Drive and going through gears and idles at 750 rpm with great throttle response and lopy idle and makes 15 inches of vaccum. All I can SAY is WOW!!!!!!!

Another success story of fixing the carb by fixing the ignition...