1997 Merc 9.9 two stroke dies when advancing throttle

[TrenchFisherman]

I just picked up a used 97 merc two stroke 9.9 hp for my 16foot aluminum boat. It is a non tiller version. Finally took it out this weekend and it started great and idles fine. Pulled away from the launch and again no problems. I try to throttle up and as soon as i do the motor starts to lose power and eventually cuts out. It will then start up no problem and idle fine but just won't go up to full power under load. If i keep it in neutral and throttle it up with just the console lever the engine works fine. It only happens when it is under load and in gear. Any ideas? I just purchased a carb rebuild kit, will change the fuel lines, replace spark plugs before my next trip out but I am wondering if I could be missing anything? I don't think it could be timing as it works fine while in neutral but i could be wrong. Also, I removed the fuel cap and still had the same issue so it isn't a venting problem.

Thanks for your time!

 

[flyingscott]

open the low speed screw an 1/8 turn at a time.

 

[Texasmark]

open the low speed screw an 1/8 turn at a time.

That's the test for the correct position of the low speed screw.......open it up as stated until the boat takes throttle, especially coming out of the "hole" and getting on plane.

 

[TrenchFisherman]

so you don't think it has anything to do with carb/fuel pump? mainly, just a setting issue? should i not even bother with the new fuel line? i figured i would just clean and rebuild the carb since it is 28 years old and wanted to eliminate any questions in there but maybe i will just start with the low speed. thanks again!

 

[racerone]

Agreed----Open 1/8th turn at a time ----test run on the boat.

 

[cyclops222]

Did you look at every sparkplug ? No black stuff on them ? Right plug number ?

 

[Texasmark]

so you don't think it has anything to do with carb/fuel pump? mainly, just a setting issue? should i not even bother with the new fuel line? i figured i would just clean and rebuild the carb since it is 28 years old and wanted to eliminate any questions in there but maybe i will just start with the low speed. thanks again!

Don't waste your time nor money chasing a ghost. Do as directed and if that isn't the problem THEN start your worrying.

 

[cyclops222]

If your dock is normal strength ? You can do all the idle in forward gear while tied to the dock. Up to a very fast idle should be no problem for the dock. After reliable dock loading tests. I take a boat out on the water for higher power testing.