ive seen many of these with the small passage in the fuel bowl nut
clogged. you can take the nut off and use a needle or a tag wire to run
thru it and then blow it out. this is also a good time to take the fuel
bowl off and was it out. if you still have a problem after this. i
would snug up the head bolts, check the flywheel key to see if its
partially sheared. there is a oring that goes on between the engine and
the carb that may be worn,, or the tube that the oring goes on may be
worn ,and a gasket on the other end of that tube that may have blew.its
easy to check the intake tube while your checking flywheel key. .....
another common problem is the valve clearance closes up so the valves
dont shut as well. you can use a file between the lifter and valve stem
to get the clearance back where it should be..006 intake,,,.011 ex.at
top dead center.. lucas.