nastyrs wrote:how come a carb cant be manipulated to act like fuel injection on the
street .. buying sparkplugs every other week sucks.. the street carbs
beit a 4150 or 4500 with powervalves only really run lean at idle.. seems
the low speed cruising is where the rich a/f ratio is horrible.. .. i want to
have sparkplugs last... this is 2007 where is the technology for such
matters .. comon !!!!
First it would be great if you posted more information about the
combination so that people would have a better understanding of
what you are working with. The title of this thread stated a “big
solid roller cam" ; please describe big
From the information provided it sounds like you have a specific
problem. The engine runs clean at idle yet it’s rich at cruse. Others
described the individual circuits that can be tuned, first you need
to understand exactly what the problem is. Are the power valves
open at cruse?
Years ago the carburetor was blamed when the ignition delivered a
weak spark. Poor ignition and intermittent misfires caused havoc
during overlap disrupting signal to the carburetor. With capacitive
discharge ignition most of these ignition related carburetor problems
went away. Check to make sure the ignition system is working
correctly. What ignition system are you running? How much ignition
advance are you running at cruse?
Another factor is combustion chamber design and flame speed at the
RPM of the problem. Even if the ignition is up to par, the expanding
gases from slow burn can disrupt carburetor signal. What cylinder
head are you running? Pull the carb. What color are the runners in
the intake? Are they black?
The people that don’t understand will smirk when they read this: It is
possible to improve burn speed at idle and low RPM with a “big solid
roller” to a point where the engine will idle below 800 RPM cold with
out fouling the plugs. Once you confirm all problems are resolved, the
key is to improve burn speed to reduce pressure pulses in the intake
track during overlap. Speed up the burn rate and spark plugs will last
so long you’ll replace them because you are tired of looking at them.