I have a 1990 40hp yamaha precision outboard

So here I am, I bought a boat, ’79 whaler 13′ classic. Came with a ’90 yamaha 40hp precision 2 stroke. I didn’t get the chance to really look it over before the buy. It was my good friends boat and long story short he passed, I couldn’t see it fall into the wrong hands. New battery, fresh gas, fired right up with a look at the key. Hooked it up and took it to the ramp, idled a good ten or fifteen on the way out of no wake, opened it up real slow in open water, started getting up on plane with no issues, right as it got on plane it literally sounded like it was slipping out of gear… so I circled, ran it up slow again, same thing.. circled a third time and limped it back in. Made it to the ramp and watched people “learning to load”, loaded it up, came home, flushed it with the muffs and rinsed it off. On the way back at a decent idle (no wake) I could hear this knock almost like a misfire but more likely a more mechanical issue (because of the slippage). It was shrink wrapped until yesterday, it was fogged as well before they stored it. Fuel/water separator was working good. I feel like the one thing they REALLY should’ve done they didn’t do…and that’s change the gear oil before the winterized it. I’m hoping that the fluid is just low and that’s why it’s popping out of gear? (This is my actual question) could a low fluid level cause that issue like it does in a car? Or has the clutch dog ground off all the forward gear teeth.. it was the only thing I didn’t check as the motor was just to have been rebuilt last year… was the gear oil…but I took it easy on her just in case…fate favors the patient. Advice would be greatly appreciated. Thanks in advance!

A couple of things you can check, drain the gear oil and look for glitter and pieces of metal, that will tell you what is wrong real quick.
take the prop off and have a prop shop check to see if the hub is spun out and slipping.

I have a ten year newer motor than yours in my shop right now with the clutch dog and forward gear out of it, someone didnt rig the shift cable properly and it destroyed both of those pieces, and, the prop shaft is bent, between the cost of the gears, shaft, bearing and seal kit combined with labor it was cheaper to buy a lower unit and ship this one out for the core.

By the time I got back, all places for gear oil were closed…ugh, tomorrow if I can find a place with some oil I’m going to pump it and fill it, I was going to check for metal just for that one reason. How would I be able to check the steering linkage adjustments?? Good looking out!

Steering linkages?? I think you meant shift linkage considering how you have a problem with the lower unit?
if that is what you meant and how I do it is this, unhook the shift linkage at the motor and manually shift fully into forward gear, verify this by grabbing the prop and make sure its fully engaged in gear in one direction and ratchets the other direction. (make sure the kill switch is switched to off, trust me a motor can fire, dont ask me how I know )

adjust your shift cable to match up dead center eye to pin, now, manually shift the motor to reverse and again check the lower unit for full engagement, shift the cable to reverse and see if the eye and pin line up dead center, if it does most likely neutral will be on the money, however, there are times due to play in the control, slop in the cable, etc you will have to find a happy medium with the cable adjustments but make dang sure it shifts fully into gear both directions, if not, you will have to replace the cable and or control.

If your Yamaha is like the ones I have been working on there is another adjustment in the lower unit shift shaft and that is something that takes a bit of finesse to adjust and you have to know what you are doing, if you dont pay a pro to do it other wise you can end up with problems.

hope that makes sense

Makes a LOT of sense…also, are you really in Iowa??? I can’t bring my unit in that far away!! Also, where the heck would you find a lower unit for this thing if it came to that??

send me your model and serial number and I will look it up for you and try to find one.
and yes, I live and work in Iowa, my shop is in Kellogg Iowa,, its one of those small towns where the population never changes,,??? yep, some gal gets pregnant and some guy leaves town lol.

So I drained the gear oil just now, I don’t see any flaking…which I’m kind of surprised about. So I’m assuming that I’m left with a bad shifting linkage setup and it hasn’t ground off the forward gear all the way….or the props spun. Apart from a little air, the fluid looks brand new as well… any suggestions? Model number is 40etld, code :6h4-L, serial no:560163.
Also I included 3 photos, first of the oil, second is a cracked “mount” (the bottom is solid, top has corrosion) and the third is down on the foot, like a weird place for corrosion, and a crack that weeps water… I don’t know if I should be looking for a whole new motor at this point and if this will even make it through this summer, I has most likely been running like this for awhile

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Also….I just checked the linkage, for the most part the forward gear was about on revolution of the plastic connector off dead center, once I checked the prop, did as you said, check the reverse, it was a one revolution off dead center after I had adjusted the forward gear linkage so I left it alone as it still engaged. However, I did realize that when engaged in reverse the prop does not ratchet like forward, it is locked in gear either way spinning. As for this linkage being the problem…I don’t think that’s it, I get that a MM means a lot when gears are meshing together, but I seen no flakes in oil…so it’s either fine?, or I didn’t abuse it enough to make more flakes, and all the flakes were gone because they changed out the gear oil when they winterized it? I would imagine I’d still see some though and I seen none. So I think what you’re telling me is either the props spun or its the sneaky adjustment in the lower end that I can’t get to..

Prop/hub is easy to check. Take a marker or paint and put a mark across the joint between the prop and hub (so it marks the prop and hub). Take it out and run it till the problem presents itself. Then, look at your mark. If the hub is spinning, the marks will no longer line up.

so here’s my next update, I put it in the water, got out into the bay, opened it up, started catching air under the prop, dropped the tilt a little more and started running good, in fact, it ran good enough to venture a little further. I had a first mate with me (case she had to paddle…captains don’t paddle lol), I got it into open water (ocean) and got through some swells, ended up in Oak Bluffs which is on Martha’s Vine (from the cape, thats about a 15-20 minute haul through some chop) and it ran strong. Opened it up pretty good once we hit the reef in the slick water. Letting the engine cool now a little before I head back, as I didn’t see a good stream coming from the impeller even when I was going 3/4. I’ll send another update after we get back!

If it was taken apart for rebuilding or whatever, it would be easy to mess up the shifting adjuster while everything was taken apart or put back together.

If it only ratchets one way, adjust the cable that way, imo.

I did just that. So here’s the update….made it back from the vineyard. Went through a good chop there and back, rip was really moving with the slack tide. Ka-plowed it the whole way back. Realized that I had just enough gas to make it back.. but made it back none the less. I didn’t seem to have any real problems other than the impeller wasn’t really keeping up. I came home and jammed a piece of wire around in there and seemed to clean it out (seaweed maybe?), put the muffs on and it seemed to be peeing like a champ. All in all I think it might have been that 1 MM adjustment I made? Can’t be that right? I had met a friend of mine on an island halfway back and he was saying that maybe I was catching some aeration from unearthed because the motor might be mounted a little high on the transom. If that was the case…wouldn’t that account for the immediate drag and high Rev of the prop? Maybe I’m just sounding like a crazy person…but hey, we’re talking open water boating, can’t be too careful!! I appreciate all the help and ideas…glad I’m part of this clan

I might be wrong but I think a very small adjustment like that could fix that clunk clunk then go into gear problem. Mine did it and it was just a tiny adjustment. But man, it is loud when it does it.

small adjustments can make a big difference, remember that you are taking a lateral movement and making it a rotary movement then into a vertical lift/plunge movement.
length of movement x ratio of arm to centers = amount of end travel.