I am trying to help my dad get his pontoon boat going. It has a Honda 90 HP outboard 4 stroke motor. 6HNXM1.592GO The boat starts up and will run fine in neutral. I can rev the motor to higher rpms and it runs fine in neutral. When the boat is put in gear, it chokes out. I can get it to go into gear and run below 1000 rpm, but as soon as I accelerate it chokes out. I have drained old gas, put in new gas, replaced spark plugs, and sprayed internal combustion cleaner into intake. None of this has made any difference. Please advise as what is the appropriate next step. I am not a mechanic so if you can provide some instructions it would be appreciated. I am struggling to understand why it would run so well in neutral, but will not run in gear?

 

I'm having the same exact issue and have done all the same troubleshooting. No dice. Did you find out what was causing the issue with yours?

I have validated fuel lines are clean. Blown air back into tank with no problem. Can accelerate to high RPMs in neutral but when under load and put in gear I can only get to about 1200 RPMs before it stalls. If I baby the motor and choke it while steadily increasing throttle, I can manage to get it to 2500 RPMs. Under no circumstances have I been able to gun it and get the response it should give.

fuel filter changed with oem
New spark plugs
New fuel lines
New primer bulb
Removed fuel pumps and cleaned them up with seafoam
Clean/ new fuel
sprayed gumout in carbs LOTS of it
opened drain screws on bottom of each carb and filled with gumout and sat over night 2x.

 

if a carburetor sits a long time with fuel in it, it usually means the carb bowl may be clogging with tar. fuel drying up in the fuel bowl. take one carb off and open it up to check the insides. also clean your idle adjustment needle. check first how many turns to full close each needle then remove and clean and reinstall.

 

On some engines the timing does not advance enough to meet the load demands
Do not know if this is your issue??