Low RPM at full throttle???

[GreenGolfBall]

So, I got a 2003 21' Tracker pontoon with a Mercury 60 3 cyl. on the back. I'm having problems with not hitting 5000 RPM at full throttle. We're only hitting 3800 RPM. I've changed the fuel filter, fuel line from the tank to the motor, rebuilt the fuel pump, taken the carbs off and cleaned thoroughly, changed the foot oil also. The plugs look fine, they were replaced last year. And still only hitting 3800 RPM. Anyone have any ideas??? Sorry I won't take it to a shop. I don't trust them at all.

[Woody]

Are you running the same prop that you always have ? Has it always hit 5000 before ? Is the prop bent ?

[stickman]

Don't take this wrong, but you did ask for ideas and I am very unfamiliar with outboards - other than the extreme little I messed with my dad's as a kid. Are you using the throttle control from the helm? Is is possible you have a misadjusted/stretched cable that is not advancing the throttle at the engine?

Just throwing out ideas...

[dockholiday]

Welcome

How long have you had the boat an is this a recent problem? You could check the linkage on the throttle, to make sure it is opening all the way. I know you said you cleaned the carbs, but on my old toon I had a damaged diaphragm in the carb. Didn't know it till I let a dealer sell it, an the mechanic discovered it. Not much of a mechanic myself, but could run some seafoam through it. Any chance you are over propped?
doc

[GreenGolfBall]

Yeah, same prop that came on at the factory. I just had the boat out of the water....prop looked good. Yes we are getting full throttle. The butterfly is opening all of the way. Cables look good too. When you push the choke while full throttle, the motor will rev where its supposed to for a second and then slowly backs down to 3800 RPM.

[HandymanHerb]

Sounds like a carb problem then

[Woody]

Sounds like a carb problem then

Yep. Possible air/vacuum leak too.

[badmoonrising]

I concur...carb rebuild or replacement is the most likely culprit. Couple of things I'd check before doing so is make sure all 3 plugs are getting a strong spark. Use a spark tester or pull one plug at a time, reattach it to the wire, hold the metal body to the block (using a pair of insulated pliers ) and have someone crank it over. All three should be nice and bright. This is better done in the shade/after dark. I'd also check for coil pack leaks (mist them with a spray bottle of water, crank it over (again better done after dark) and look for arcing to ground. Very common for the coils to arc to ground when they go bad, usually arcing to the mounting bolts.

[Woody]

Good points also BMR. With him saying it gets better with the choke on, it's most likely a fuel issue though....IMO.

[GXPWeasel]

I agree as well on the carb. Those things can really give a guy some fits. Also, I know you said that the plugs were just changed last year, but I would change them anyways. Afterall, that is one of the cheapest things you can do to a boat motor for tune-up. I'm also guessing this is an outboard engine? If so, when you winterized last year, did you fog the cylenders? If so, maybe that fouled up the spark plugs?

Keep us posted.

[badmoonrising]

Good points also BMR. With him saying it gets better with the choke on, it's most likely a fuel issue though....IMO.

Yep, but it's always better to rule out ignition problems first.

[Woody]

Yep, but it's always better to rule out ignition problems first.

Nothing wrong with checking everything.

[wrenchendave]

expensively priced cheap fuel messes up the carbs on my old merc when I don't drain them and when i do drain them i get the bluish green oil residue dried up on seals . damn if you do damn you don't .

[GreenGolfBall]

Yes its an outboard. I'm going up to the boat today after work. First, I'm gonna take the fuel line and run it directly into the tank instead of the fitting where it's supposed to go and see how she runs. Then, I'll be checking the coils and the plugs again. Let's hope one of those fixes it. Keep the ideas coming guys. I appreciate it and I'll keep you posted on the outcome after today. Thanks again.

[Woody]

Sounds like you have a plan. I hope it turns out to be something simple for you. Keep us updated.