Wow, old thread. Vaccum signal from long duration cams can cause idling problems, usually can be corrected with some air bleed work on the carbs. My blower engines won't idle properly unless the mixture screws were backed way out. Put in gear and they'd die. Same carbs that were on my buddies engines, that were larger CI but milder cams, no problems, but my longer duration cams dont pull as much vacuum at idle. Hence the need to go to smaller air bleeds on my setup.

Proper carb tuning, will eliminate the surging. Too much fuel causes it. Lean them out at IDLE and they wont surge as much. And do not run water thru the intercooler at idle.

Thank you for the detailed info and thoughtful post. Much appreciated!

if a blower carb or HP series carb is being used one will need to increase the jet sizing in the idle ckt and 1st hi speed ckt... this will overcome a good chunk of the surge and leave the cool part that us blower guys love!!! a lope sounds cool but if ya can't drive the boat cause it quits going into gear it can make for a chitty boating day!!! patients and lots of trial and error are what is needed to get around this... big HP big cams and big blowers have to be tickled just the right way!!!

agreed Joe... water thru intercooler at idle is bad bad bad...

sounds like too much duration not enough blower... I'm running 10+ inches of vacuum at the lowest idle 900rpm...

I wonder if Tonto was running Whipple blowers vs roots blowers on his engines at the time of his posts to prevent the surge in his blower engines,---but he never mentioned it. The Whipple's have that pressure relief valve on the back of their blower cases that tames things down a bit during idle and supposedly improves idle quality.

with the whipple they have a bypass with a vacuum operated valve.when the intake manifold sees vacuum the valve is open and closes with boost.surge is almost non existent.

I have the reverse problem,, stock 454mag with stock cam and a B&M420 blower,,idle surges like crazy,
stock cam pulls too much vacuum and when blower surges vacuum drops,,it will swing from 18" of vacuum to 8" of vacuum,,had carbs gone thru twice by Dan DaVinci with no imprvement,,he has tried every trick in the book,,idle will not settle down unless you lean it way out and then you cant put it in gear without it dying..
I had this same setup on my last engine, 509 with custom cam and idled perfectly at 10-12" vaccum.
vid:
https://www.facebook.com/Frank.No.Pr...type=3&theater

I do not claim to be any kind of an expert, but I think if your carb guy would "boost reference" your carbs that it would help kill the surging/hunting problem for you. Perhaps someone else can chime in about boost referencing a carb for blower apps.

frank,i think it sounds bad azz.is that you racing the drag boat?