Need some help here...I have a SBC with a Performer (Weber) carb,aluminum intake and stainless marine exhaust....Motor has 42 hours on it...Well I keep up on my plugs and for about 40 hours they looked right on. Well with no changes made to the motor I started to get a slight miss on the top end and a definite miss when coming back to cruise after a W.O.T. run...When saying "cruise" I mean 32-3800 RPM's. If I bring it back far enough the miss will go away. .Usually below 3000 rpm's. Also I started getting a hesitation when going from cruise to W.O.T. I checked the plugs and they are LEAN!!!!!! What things should I look at to trouble shoot this Bit*h The miss and hesitation only happens under load. And again NO changes have been made to the motor to bring this on. The plugs were reading right on and then all of a sudden the symptoms started...In trying to figure this out I have upped the carb 2 steps (8%) on both the primary and secondary circuts and it did nothing....I have since went back and rejetted the carb to it's original settings. I have re-adjusted the valves (5/8 turn) and installed a new D.U.I distributor,New Taylor wires and new plugs. Still no changes. Plugs are white as a ghost....Any Ideas Thanks in advance

BH

Being that you did a jet change and saw no change in plug coloration, it could possibly be a fuel delivery problem. Maybe the pump is going bad? Clogged filter?
I am sure that when you did the jet change, you looked in the bowls for any dirt.

Did you check the fuel filters?

I put a new Fuel Filter/Water Seperator on also. Still no changes.
Have not checked Fuel Pressure though. Wouldn't this show up as rpm's increase regardless of load?

BH

anti-siphon valve at the tank fitting maybe?

An engine under load will require more fuel to run than an engine in nuetral.

I HAVE THE SAME SETUP AS YOU EXCEPT WITH A BIG BLOCK AND WAS HAVING A SIMMILAR PROBLEM LAST YEAR.IF YOU DO A FUEL PRESSURE CHECK AT THE CARB AND ARE HAVING NO SUBSTANTIAL PRESSURE DROP UNDER FULL LOAD CONDITION YOU CAN ELIMINATE PUMP,ANTI-SIPHON,FILTER,& LINE PROBLEMS.IN MY CASE I HAD PRESSURE AT THE CARB,BUT WHAT WAS HAPPENING IS ONE FUEL BOWL WAS RUNNING DRY.IF YOU PULL THE NEEDLE SEATS OUT THERE IS A FINE SREEN ON EACH SEAT.ON MINE THE SREEN ON THE NEEDLE SEAT OPPOSITE WHERE THE FUEL LINE ATTACHES WAS PLUGED.THE BOWLS ARE CONNECTED INTERNALY ON THE CARB SO BOTH BOWLS HAD SUFICIENT FUEL AT LOWER RPM BUT UNDER FULL LOAD WITH ONLY ONE NEEDLE SEAT FLOWING PROPERLY IT WOULD RUN OUT OF FUEL(LEAN).I WOULD LEAVE THE JETTING ALONE BECUSE IF IT WAS JETTED RITE IT SHOULD STILL BE JETTED OK.COOLER WINTER DAYS WILL MAKE THE ENGINE RUN BETTER(LEANER)BUT I WOULD NOT THINK THIS WOULD GIVE THE EXTEME LEAN CONDITION YOU ARE EXPERIENCING.GOOD LUCK!

power valve? What is the vacuum reading at the hesitation point? Greg

It' a Edelbrock (Weber/Carter)....It doesn't have a power valve.....Does it

BH

I THINK HP JUNKIE WAS GETTING AT ARE THE PRIMARY NEEDLES MOVING TO THE POWER STEP POSITION.IF YOU ROTATE THE NEEDLE HOLD DOWN CAPS YOU CAN SEE IF THE NEEDLES ARE RISING UNDER FULL LOAD TO THE RICH PORTION OF THE NEEDLE.IF IN DOUBT PUT THE HEAVY SPRINGS ON THE NEEDLES.IT IS VERY EASY TO CREATE A CRUISING LEAN CONDITION BY TO LIGHT OF SPRING.