Originally Posted by OneBadGMC
Originally Posted by olds48
Btw,the air/fuel mixture is a ratio.If your moving more air you are naturally moving extra fuel to go along with it.At the same ratio that you were before you recent modsIf your plugs are tan than it's probably not quite lean enough to stumble,especially at one constant speed.Just because you are making more power doesn't mean the your motor is less effeicient and needs a richer A/F mixture to cope.Look at the Vettes making 500+ hp and getting 20-25 mpg+.More power doesn't always mean more jet.Pop the front bowl off and stab in a PV just for the heck of it.Jist my .02c
Huh? If you're moving more air, you need more fuel to keep the same a/f ratio. You can't assume that a carb is going to automatically feed more fuel because more air is moving past the venturi.
Besides, the issue isn't at wide open, it's at part throttle. There's going to be LESS air at the same throttle blade position because of the wilder cam/heads, which will cause LESS vacuum on the emulsion tubes, and thus LESS fuel at part throttle.
Just because the plugs are tan when he checked them does not mean it's not lean at part throttle cruising.
He didn't state at what point he checked them. At the point it was surging, did he cut ignition and pull them over to check them, or did he wait until after he idled through his neighborhood and was primarily back on the idle circuit (thus throwing off the reading) to check them???
If the "wilder "setup moves more air,than the carb will meter the fuel accordingly,but at roughly the same ratio.I'm not saying that he will or will not need to rejet.But more flow does not mean that you need more jet.It is not an injection/throttlebody setup where the air and fuel are introduced to the engine seperately.When the air passes thru the carb it draw the fuel out accordingly.If the engine draws more air ,then it will naturally draw more fuel.He said that wide-open was fine,but surges at cruising speeds,that's why I SUGGESTED that he look into his part throttle tuning.Main jets are for WOT tuning