Figured I would run something past you all before I tear into my carbs. My 1973 Johnny 65hp tops out at a whoppin 3500 rpm. I have OHM tested everything and so far all test good according to the factory manual. I just picked up a spark test tool and set it at .4375 and the spark jumped really nicely so I am assuming my coils are good unless they are failing when they get warm. I am running 130 to 135 psi all cylinders. I rebuilt the carbs and linked and synched last summer but the problem wasn't cured. I am starting to wonder if my high speed jets might be slightly clogged and it is starving for fuel and that might be causing my struggling. The motor fires right up and runs smooth all the way to 3500 rpm. I am not over propped since I have my 15 pitch on at the moment and I normally run a 17. I have new fuel lines so I know those aren't bad. Now for the million dollar question. Do you think that I might have a clogged high speed jet? The only thing I haven't tested is the fuel pump and it may be getting tired. I have a 3lb electric that I plan to hook inline with a 1.5lb pressure regulator just for testing purposes. May leave it as a backup. I did forget to mention that the motor acts like it is going to go to a higher RPM but right about when it hits 4k on the tach i feel it just drop and I sit at 3500 to 3700. So does this sound like a possible clogged jet(s) or a coil failing when it gets warm? Does it right from the start on an cold motor too. At this point I will try just about anything. Also replaced the head gasket and thermostat and over temp sensor last year and have done the compression tests post repair.
SID
SID