Johnson 8hp with no power. Runs great

[summitlt]

Recently picked up a 1985 johnson 8hp. Boat used to be powered by an 84 Chrysler 7.5 and a 56 Royal Scott Atwater 5hp. Both would plane out my 12' streamliner. The 7.5 would do 19mph on GPS with two guys, trolling motor and gear. This johnson won't plane out with just me in it. Tried trimming it at every setting, motor height is good. Plugs look perfect.

Prop has no markings on it but "looks" right. isn't over revving, just seems like its a 4hp. Serial numbers match to an 8hp so its not just an 8 cowl. Checked carb and it is going WOT.

What am I missing?

 

[boobie]

Re: Johnson 8hp with no power. Runs great

Sounds like it's running on one cyl.

 

[summitlt]

Re: Johnson 8hp with no power. Runs great

Sounds like it's running on one cyl.

Both plugs look good.

 

[steelespike]

Re: Johnson 8hp with no power. Runs great

Unhook one plug wire at a time and ground it and see if it runs on the other.
Try a touch of choke at wot.

 

[summitlt]

Re: Johnson 8hp with no power. Runs great

Alright, messed with the motor today.

Checked spark and have good spark, replaced the plugs anyway. Checked compression and have 110psi on each cylinder. Pulled the carb and found nothing at all. Jets were all clean and pulled the aluminum covers and found nothing again. Am I missing something? There are videos on youtube of this motor doing 19mph on a 12' aluminum and planing out a 14. I cant get this thing close to planing a 12' streamliner.

Also just checked out some more videos to hear what ones that are right sound like, my boat definitely isn't getting top RPM. The prop has no markings but I can imagine that its so far off that it wont push a 12' aluminum. Ive looked and can only find 8 and 9 pitch props.

 

[cdunn]

Re: Johnson 8hp with no power. Runs great

Alright, messed with the motor today.

Checked spark and have good spark, replaced the plugs anyway. Checked compression and have 110psi on each cylinder. Pulled the carb and found nothing at all. Jets were all clean and pulled the aluminum covers and found nothing again. Am I missing something? There are videos on youtube of this motor doing 19mph on a 12' aluminum and planing out a 14. I cant get this thing close to planing a 12' streamliner.

Also just checked out some more videos to hear what ones that are right sound like, my boat definitely isn't getting top RPM. The prop has no markings but I can imagine that its so far off that it wont push a 12' aluminum. Ive looked and can only find 8 and 9 pitch props.

I have a 8hp Johnson with the same problem. Did you ever get this problem solved?