Full throttle goes to Idle

I have a 1988 sprint bass boat with a 110 Johnson. The boat runs great up until I go gull throttle. This is my first boat and I was wondering what it could be. Without going full throttle I have gotten it up to 37mph. However, once I go full throttle it instantly goes to idle. I'm not sure if 37 is all it will go or if there is an actual problem. I was just wondering if anyone knew what it could be, thanks.

 

Defeats me. What rpm gives you 37mph ?

 

I believe it was running between 2,500 and 3,200 rpms. I am going to take it out tomorrow and hopefully will be able to give a better description of what is happening.

 

Examine your throttle linkages. It sounds like a full throttle setting is causing the throttle plate to close. You may be able to do an easy fix for this problem. The engine is surely capable and willing to turn 5000 or more.

If the engine is an EFI type there will be throttle position sensors. That'll be an electronic do-dad that communicates with the engine control module. The problem could be a bit more complicated if there is something wrong with one of the electronic feedback components. There will be several of them, including a mass air sensor and maybe even an O2 sensor. None of this is mind bending technology but appropriate test equipment may be necessary to diagnose the problem.

Check the throttle linkages for the first round of inspections.

 

I agree the throttle linkages need to be checked, I can't imagine how it would be returning to the idle setting, though, as the throttle is opened. But, take the cowl off and see what happens as the throttle is fully opened (motor not running) as regards carb butterfly opening etc. This motor would not be EFI,imo.

 

Agreed, it's likely something simple, but could be a few different, some subtle issues at play. The first part you should buy for your boat is an engine manual.

 

Long shot... clogged fuel filters and water filters caused weird things to happen to me before.

 

Filters usually act up regardless of throttle settings.

 

Breather on the fuel tank cap? Enough to stop a 25 or 40 from full chat at 5k rpm.....

 

It is a case of losing revs sharply, not just not getting maximum revs, so I'd doubt that could be involved.

 

Maybe, but funny things happen if you get a partial vacuum from the fuel tank. It is also worth checking that the breather actually breathes, I have known the internal passageway of the breather cap to become clogged too.

If it is a carb engine (and not fuel supply/breather problem), I'd be cleaning out the floatbowls, passageways and jets because by half throttle the engine is running on main jet and needle pretty much exclusively.