At wits end......
Thanks guys, probably doing it at 3000rpms at first.
Then more likely fuel than springs...especially since it did it with another carb. A coupla checks I would do:
- measure the fuel pressure at idle
- see how much pumps into an open can in 30 seconds of cranking
- start engine cold then stop it, and then remove the fuel line to the carb to see if there is residual pressure in the line; a good outlet check valve should hold pressure for many minutes
- run it WOT to stumbling for a few seconds, then immediately close the throttle and shut off the ignition and shift into neutral at the same moment so the pumps stops right away; drift to a stop and see if the fuel in the bowl is at the right level
Have you cleaned the fuel tank and sock on the fuel pickup? You could just have a bunch of crud restricting the flow.
But what DO you have for springs? Stock cam and lifters?
Possibly ignition related and could be anything that makes a weak spark:
- Wrong spark plug gap
- Weak coil
- Wrong ballast resistor
- Poor wires
But you would probably see other issues with weak spark so that seems least likely.