70hp johnson problems

[taz1127]

hi everyone i have 77 johnson ob it only goes 5 mph and when full throttle you hear it rev up and down up and down almost like its getting gas then not but put fresh fuel changed the lines and new plugs and if anyone has other suggestion please i would like to know where else to start looking

 

[ezeke]

Re: 70hp johnson problems

Take the spark plugs out and do a compression test, then a spark test.

Make sure that the ignition coils are wired to the correct plugs. What do the tips of your spark plugs look like? Have you done a de-carbon treatment? Do you have a service manual?

Has anyone had the flywheel off?