Motor boggs down at 3/4 throttle

[tjakobic]

I have a 1977 85hp mariner ob. I replaced the spark plugs last spring and noticed that the motor boggs down when I put the throttle down 3/4 of the way. Could this be a spark plug issue, fuel issue, or a carb issue? I appreciate any info any of you can give.

 

[Texasmark]

Says to me you aren't getting enough fuel.....clogged carbs, bad fuel pump, on a '77 could have cracked fuel lines letting air in and the "good" if that's what it is fuel pump can't suck enough fuel because it's adding air. Squeezing the primer bulb when the problem occurs can tell you if you have to help the fuel pump supply fuel to the engine.

 

[tjakobic]

It doesn't do it every time just most. If I had a carb issue would happen every time?

 

[Texasmark]

Depends. If varnish, it may stay put like paint or it may have flakes that float around which would cause an intermittent condition, or your float could be sticking periodically in the carb(s), or you could bump a bad hose on some outings and not others.

 

[tjakobic]

I am replacing the primer bulb and lines. Think there is a leak in there somewhere.