1988 25 Johnson having trouble starting, stuttering at full throttle

[25 Johnson]

Have a 1988 25 hp Johnson outboard. I pull start it. It takes many pulls to get started once I do I have to open the carb for a while when its in neutral to warm it up. If I don't it will shut off and I can't idle it to shift it to drive. Once I get it in gear it runs good at first and i can put it in full throttle with no problem, but once I reduce the speed or idle it won't go full throttle smoothly. When I open the throttle up it stutters, makes boom, boom, boom sound, and doesn't run fast or smoothly. Eventually it just shuts off and I can't get it started for another day. I can get it into gear once a day and it does the same thing. I've replaced the spark plugs and drained the fuel and put new fuel in. What could it be? and how can I fix it?

 

[tashasdaddy]

Re: 1988 25 Johnson having trouble starting, stuttering at full throttle

you replace spark plugs, but did you check spark. have you check compression? when was the carb last cleaned and rebuilt? boom like a back fire, gun being shot, or boom, like the boat is hitting something.

 

[25 Johnson]

Re: 1988 25 Johnson having trouble starting, stuttering at full throttle

Wouldn't say boom like a gunshot but its hard to explain when you put at full throttle it goes voom voom voom. You back off it runs smoothly. Increase the throttle and it stutters again. I planned on cleaning the carb next. How do you check compression?