2005 Mercury 90 Fourstroke Shifting Hard

[Fire93Medic]

Although my engine does not sit on a Boston Whaler boat, i know [the Mercury 90 FOURSTOKE c.2005] was a popular engine for them, and I thought this would be a good place to ask [about hard shifting].

I have a 2005 Mercury 90-HP FOURSTROKE. I just picked up the boat last year (18’ Cape Craft) for a great price. The carburetors were a little dirty. I learned this engine can be very temperamental with anything but perfect fuel. Most of my experience is with V6 OX66’s. We got the engine running well but the shifting in and out of gear is very hard.

I disconnected the [mechanical shift and throttle] cables and the [throttle and shift levers] moved freely. It tells me the sticking point is in the engine. I saw some old posts about this same problem but couldn’t find any solution--if there is one.

Any help would be greatly appreciated

Thanks--Andrew

[jimh]

A Mercury 90 FOURSTROKE from c.2005 is probably a Yamaha powerhead mated to a Mercury midsection and gearcase. Mercury gearcases from this epoch are a bit notorious for shifting with a CLUNK. Generally you have to have the engine running at idle speed and operate the shift lever rapidly. A slow movement just causes chattering and clashing of the gears.

[Phil T]

The archives include information that members who ran Mercury Quickleen in their fuel had less carburetor related problems.

What prop and hub are you running? I recall that some prop/hub combinations made the hard shifting worse.

[Fire93Medic]

Thanks for the info. Hoping to back the boat into the garage to start some early cleanup and I will take the lower unit off and see how it shifts from there. I am not sure the prop off hand, but I’ll take a look and report back.

[kwik_wurk]

There is a notable difference between "hard to shift" and "shifts hard".

Mercury lower units of [2005] vintage and [90] horsepower like quick shifts or quick transitions between F/N/R. If you have a stainless steel propeller, a "tired" hub, and shifting out of the water, you will get a good CLUNK from the lower unit. Take off the propeller if you plan on doing a lot of lower unit work and shifting whilst out of the water.

Pulling off the lower unit is one thing. But the shift rod connection is rather straightforward, so if it there is binding, there is going to be a lot of stuff gumming up and other problems. You really can't do too much if the gears are actually bad.

And you might as well get and install an impeller kit if you're inclined; you've basically done half the work.