Idle pulse?????

[custom-cruiser]

My idle pulses from 1000rpm to 1500rpm. Is this always a vacuum leak? It smoothes out if I crank the idle screw up to 1500rpm but that is a little hairy around the dock.
Set up is:468 w/871 BDS, duel 750 4150's,powervalves plugged, squared at 76's,nice tan color on the plugs,37 deg. total advance,four corner idle at one turn out. No stumble,loading up or coughing out of the hole.
Any suggestions or tuning tips???? http://free.***boat.net/ubb/biggrin.gif

[RumRunner]

It could be a few things. First you may not have enough initial timing in the engine. Double check that, next your carburetors may be a touch lean. Once you've checked, and reset your timing, start the engine than at idle (once up to temp) push on your acc. pump arms without moving the throttle linkage. This will add fuel without changing the amount of air the engine sees. If the RPM goes up, it's lean, and needs more fuel, if it drops you may be too rich already. Try readjusting your mixture screws, and going from there.

[Unchained]

Custom Cruiser, My engine started doing the blower surge when I got up to 27% overdrive with an 8-71 on 540 CI. I was not able to tune it out by changing timing or idle mixture. I run the ign. timing locked in at 34 degrees. I think it sounds bad to the bone.

[superdave013]

It's hard to get them to not surge like that. It's going rich and lean with the pulsation of the blower. It's pretty much the way it is when you're running gas. If you think it's bad now slap a fuel injector hat on it and it will surge way more. But it will be lots snapper too. http://free.***boat.net/ubb/smile.gif
37 deg of timming hu? That's alot on a blown engine. I would suggest you backing that down to around 32 total. You could burn a piston real easy with the aount of timming you have now.
I can't remember the exact jet size but I know I was running bigger one than that. But I might have been running more over drive then you. Mine was @ 12% I think. I ran it on ave gas back then. What kind of fuel are you running?

[custom-cruiser]

Thanks for the tips...I'll get to work.
SD. I was thinking of backing timing down to 34 but maybe I'll start at 32. My pistons are 8:1 and blower is under driven so boost(6lbs) does not even kick in till about 4000rpm. Come to think of it with last years two 600 Carters it did about the same thing.
Maybe if I over drive the motor a little it might smooth out? I just run premium with the occasional bottle of octane boost.
Didnt you say you had some Bottom 8mm blower pullys with the 3 hole mount? right now I have 54 bottom and 59 top.
CC