50 hp 1980 johnson sputtering

[jacksonboater]

1980 50 seahorse. I have rebuilt carbs they were immaculate when broken down. I have not checked compression but it sputters pops and shutters while running. starts right up and will stay running for at least five minutes. Good spark on both cylinders.
What else could be wrong? Any help will be appreciated

 

[jacobcnc]

Re: 50 hp 1980 johnson sputtering

Air leak in a gas line

 

[jacksonboater]

Re: 50 hp 1980 johnson sputtering

Would the leak not be obvious under pressure with the motor off? How do you isolate an air leak?