Missing some RPM's

[ripnlips]

Have a 60HP Merc 4 stroke 1yr old. Should be able to get 5500 RPM out of motor. Most I get is around 4000. Granted, I've been running with my kicker down, but that shouldn't affect rpm. Any ideas? Thanks.

[garyk]

Could it be the pitch of the prop? A higher pitched prop grabs the water more aggressively, but take it too far and it overloads the engine.

[jokester]

I'm interested in the responses too!! My friend has a newer 90HP Honda 4-stroke and he's having the same problems. He usually gets somewhere in the neighborhood of 5000-5500 RPM's at full throttle and he can't get anything over 4100??? When the motor's in nuetral, it revs like there's nothing wrong and he can get full RPM's out of it!?!? :eek: It's only happening when there's a load on the motor. This just started happening about 2 months ago after he got back from his trip to BC.


-jokester

[1pump]

If you've never gotten over 4K out of it EVER, it's probably over-propped. If you bought it new, and the dealer didn't help you get it set up, I'd be a little ticked.

If it's not, start checking the simple stuff- kinked or improperly adjusted cables, plugged filter, etc before you start tearing into carbs.
Excess drag on the hull can do it, too, but the kicker probably isn't enough by itself.

[12pulls]

Running with your kicker in the water can result in cavitation problems with your kicker if it is dragging in the water.

[ripnlips]

Have run it over 5000 before, but the last couple times out 4000 is the best I can get. Can understand the kicker affecting speed but I wouldn't think RPM's. Not an expert though. Any chance a plug has gone wrong? Idles really smooth, trolls at 850 rpm very smoothly so I didn't think a plug was the culprit. Has me baffled, but, I'm just an insurance agent.

[BungaBunga]

Ripn, I'm no mechanic but from all I've heard and read having your kicker in the water is exerting tremendous drag on your boat. That drag is one big reason some guys will chose one large outboard rather than two smaller ones on a big boat, same combined horsepower isn't nearly enough to overcome the extra drag of having the second lower unit in the water. (Water doesn't compress, sticking the edge of your hand in the water at speed will illustrate, but hold on! and don't tell the rescue crew I told you to do this.) Also, by holding the boat speed down it does hold your rpm down too, at the lower speed your prop would have to completely cavitate to get up to its usual higher rpm.

Try a comparison run with the kicker up once, and then down. If you can't get your normal rpm with the kicker out of the water, then suspect a motor problem. Good luck!

[jokester]

I know for a fact that my friend doesn't run with his kicker down, so what are some things (motor wise) that ripnlips can start to take a look at if the kicker is not a problem? As of now, my friend is planning on putting in new plugs, plug wires, fuel filter, etc??? :shrug: Anything else??

-jokester

[MacEFL]

Run with the kicker up. His post said he runs with it down! Go to a prop shop and try props till rpms where you want them!

[BungaBunga]

Jokester, with your buddy's motor being that new I would say if the easy stuff (plugs, wires, fresh gas, and fuel filter) don't bring it back up to normal, it's time to take it straight to the Honda dealer he bought it from.

[bellinghamangler]

You may not be firing on one cylinder, something to check into anyway.