I have been running my webers for some time now with a pump from a yamaha r1 but allways had the problem with fuel starvation at high rpm, so i invested in a red top pump with a filter king regulator with a pressure guage in-line. engine is a 9a block , mild p&p kr head , 278 deg. kent cams , 2 1/4 inch exhaust , megajolt ignition. main jet 145, f16 tube , 175 airs , 60f8 idle, 45 pump jet , 2.0 needle , plastic floats , 36 choke , weber 45 152 .Fuel perssure is set to 2.5 psi, floats are set to 12mm with gasket in place. Before i changed the pump the fuel pressure was reading 1psi, no suprise there, however the engine ran really well, no flat spots, good pull and acceleration but fuel starvation at high revs. After fitting the red top pump, i have a stall at low rpm wilst accelerating and a cough from the carbs, and a popping from the exhaust while decelerating trottle closed. I tough the carbs were lean but with a 60f8 idle jet? I use a color tune to set the idle screw and to get a good idle. The mix screw is out nearly 4 turns, with the yamaha pump this was 1 1/2 turns. If i fully wind the screw out to 6 turns i can't get the carbs to burn rich, i.e an orange flame. I presumed the carbs were dirty so have striped and cleaned them but the problem remains. It looks like i need a larger idle jet, but larger than 60f8???? Altering the fuel pressure guage to 1psi makes no change to the problem. Something is wrong here and i can't figure this out, any ideas
All looks good... I'd have started with more or less the very same settings apart from maybe 55 F8 or F9's. Maybe worth a try with 60F9's, but I'd up the fuel pressure to 3psi to start with before changing anymore jets.
It just happens i had a set of 55f9's in the garage and fitted them. I had to screw the idle mix screw in about 3/4 of a turn and there is some improvement, the flat spot at 1800-2400 rmp is gone but there is still a backfire from the inlet and a heavy popping from the exhaust on over run. I think i need 50f8 jets, should do the trick. On a test run the backfire in the inlet blew the vacuum connection for the brake servo off , on the motorway at 120kph, no brakes..........brown trouser moment.
