2004 115hp Optimax Not Topping Out

Hi. I have a 2004 Optimax 115. It's rated to top out at 5750 rpm's, but according to the smart guages it's topping out at about 4800 rpm. I have also lost some top-end speed, it used to hit about 42 mph and now it'll only get to about 35 mph. Other than that, it runs GREAT and idles perfectly. If I hadn't noticed the loss in top speed (based on GPS) and the lower than rated max rpm, I would never imagine there was anything wrong with it. I have replaced plugs and fuel filter. Any ideas on this one? Thanks to the Group Mind.

I haventaclue about an Optimax,but I''ll hazard a guess and say check your boat for water ingress,bottom for growth.Because if everything is running as it was before,just slower and lower RPM's then something is adding substantial weight.After that I'll leave it to the experts.

Did you ever get it up into the 5700'ish rpm range?

Was there a prop change anytime prior to noticing this drop in performance? anything else change (added weight to the boat?)

While on the water if you put it in neutral and wind her up what rpms are you getting? (give it a try).

But as suggested you might have a soggy hull that has added many pounds to the overall weight which would "slow things down".

While on the water if you put it in neutral and wind her up what rpms are you getting? (give it a try).

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Please don't do this!!!! It will tell you nothng an could result in a runaway or damage to engine! Have you changed the air filter? Have you change the air muffler? The fuel filter you replaced was it the VST filter or water separator?

Thanks for the thoughts so far. I'm confident it's not a change in weight or the hull. This is an aluminum boat that I trailer with the plug out (Minnesota law) and only use once every week or two. No prop changes or anything like that. I am not sure if the rpm's used to run higher. I noticed the loss of top end speed first, then later noticed that the motor is rated for higher rpm than what I'm running. The filter I replaced was the red one with six tabs, I'm not sure if that's VST or water separator? Plugs are the only other thing I have replaced.

I will check on the air filter, air muffler, and the other fuel filter.

Based on some Google searching, it sounds like some people have seen similar issues with broken reeds. This means nothing to me. Any thoughts on it?

Thanks again for all of the free advice.

The filter you replaced was the VST filter and reeds was next after you checked other items. To check reeds remove front air cover and start on hose. Listen to the throttle body and if you hear a puft puft sound that usually a chipped or broken reed and it will still idle great just a 100 or so rpms lower.