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Yamaha 90hp outboard help

8K views 18 replies 12 participants last post by  Rat~Man 
#1 · (Edited)
Anyone familiar with Yamaha outboards?

I'm trying to help my Dad get his boat going as he is no longer physically able to participate in his normal summer obsession, golf (he has cancer, incurable, but they give him a couple years).

The boat has been sitting in the barn for a few years, ran rough the last time he used it and it hasn't been much of a priority since. He also said the last time he used it it would idle and rev fine, but fell on it's face when you put a load on it.

I pulled it out the other day, pulled, cleaned, and re-assembled the carbs. I can get it to start pretty reliably, but it idles really rough and dies after 10-20 secs of idling. If i give it throttle I can sometimes get it to run, but the rpm's seem to run away til i cut it back then it idles and dies.

This motor has the oil injection system, and I'm noticing a lot of 2-stroke oil in the water tank, as well as the spark plugs being heavily coated in oil.

Any idea where I should start on this thing?

I'm thinking part of the problem may be over-oiling from the injection system. I put a couple of gallons of pre-mixed 50:1 gas in the tank, pinched off the oil line from the reservoir, cleaned the plugs and it was able to idle for closer to a minute before it died. I'm going to get new plugs this week and possibly get a new fuel pump since it's pretty cheap, just to eliminate that as a problem.

I've also noticed that it will not start without the motor cover on unless I give it a shot of ether. then I can see fuel being sprayed from the jets when I increase throttle, but it will not idle at all without the cover.

Is not running without the cover normal? I'm not really familiar with outboards or 2-stroke engines in general, but I have an old 9.9hp evinrude that does the same thing.

Sorry for the long post.
 
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#4 ·
ok, downloaded the manual online. Looks like there is a valve beside the middle carb that can be switched on to enrichen the fuel mixture. There doesn't seem to be an actual choke, at least there is no mention of it in the manual.

I'll check that out when I get back down there. I pulled the fuel filter and checked it, it looked very clean (two piece design) so I don't think that's the issue.
 
#5 ·
Check the coil packs. There should be test procedures in the manual. If the coils aren't strong, that'll throw everything else off. If the coils are good and the fuel enrichment valve isn't stuck, do a compression test.

A friend of mine has a yamaha 115 4-stroke that he just bought that had been sitting for years. It still didn't want to run right after cleaning the injectors, replacing fuel and filters, checking plugs, etc. So he brought it to the shop and it turns out the compression was down to about 30%. Before they tore the motor apart, they mixed up some kind of concoction and ran it at idle for a few hours. It must have been really gummed up valves because that's all it took and the boat runs like a champ now (supposedly, it still hasn't been picked up).

If all of that seems good, I'd bypass the oil injection. On my Johnson, it's just a matter of pulling the electrical connector and oil lines and plugging the ports. It's probably something similar on the yamaha. I'm sure it's been discussed on the internet; it's a pretty common thing to do.
 
#6 ·
on the yamaha the oil pump is mechanically driven. I've found a few threads about guys switching over to pre-mix and eliminating the injection. There is also a sensor in the oil reservoir that sets off a buzzer if the oil gets low. I think it will also prevent the engine from exceeding a certain rpm, so I'll have to look into that before eliminating the injection system. I'll take my compression tester over there too, can't hurt to check.

I've got some sea foam I plan on running through the fuel system too, might not hurt to run some through the oil system as well.
 
#7 ·
Yamaha oil injection rarely gives any problems, I'd leave it there. Start with a compression test, then use a spark checker to insure you are getting spark on each wire. Pump up the primer bulb and squeeze it pretty hard, does it go down? are you getting any fuel dripping around the carbs?

What did you clean the carbs with? Yamaha carbs have extremely small orifices in them. I use an ultra sonic to clean most of the crud off, then dunk the carb bodies in "Yamaha carb cleaner" for at least a few hours. @ qts in a folgers coffee jug works just fine. Then back in the final ultrasonic to final clean, blow them out good with air and reassemble. The enrichment circuit use stator voltage to heat a wax pellet inside the needle assembly, when the wax is cold, it holds the needle off the seat, allowing extra fuel to enrich en the circuit. Once the wax heats up and melts, it moves the needle closing off the extra gas,

Sounds like to me you need to have another run at the carbs, I have to go back once in a while to clean them a second time. Don't use old school chem dip on those carbs. The Japanese carb manufactures use soem really crappy aluminum to make carbs, teh alumiun is sometimes poures, they coat the carbs with some kind of clear coat to prevent internal air leaks. Thats why they look kinda shiny. Post up the engine model and I'll see what teh idle screws are supposed to be set at
 
#8 ·
Clean the carbs first as in completely disassemble them and clean every orifice, jet etc. Make sure the oil tank is full as some of them have a low oil sensor that puts the motor in limp mode. Make sure the oil tank caps are in good shape and not cracked since a tiny amount of water in the oil system will cause a toasted motor.

Sent from my A500 using Tapatalk 2
 
#11 · (Edited)
I've worked on any number of Yamaha motorcycles (never on outbooard, though). It sounds like your ignition system may not be functioning correctly, as stated previously. That's where I would start. Yamaha oil injection system is damn near bullet-proof. Another thing to consider is the brand of two-stroke oil you're using. Are you using "black death" 2-stroke oil (cheap Wal-Mart-esque 2-stroke that sells for $5/ocean-going-tanker full) or are you using a good (i.e., expensive) synthetic, like Golden-Spectro or similar that actually works? Can't tell you the number of spark plugs I seen fouled/ruined by running black death 2-stroke. In the long run using cheap oil is WAY more expensive.

EDIT---> Also check the crankshaft seals. Believe or not, these have a BIG effect on how a 2-stroke runs, along with reed valves (if your outboard has these).
 
#14 ·
Stopped by the local boat shop on my lunch break. Went in looking for a fuel pump, talked to the counter guy/mechanic who said if it's starting and idling at all the fuel pump is fine. Recommended doing the carb soak and said the same thing that SparePartsDave did about soaking the carb and small orifices etc. So I picked up some of the yamaha carb cleaner and will be taking them back apart and giving them a thorough cleaning. I'll update after that.

Also picked up the yamaha brand 2-stroke oil, which is what has been used in it since he got it (bough used so I don't know what the previous owner ran).

Thanks to everyone for the help so far, I've got to get this thing going. If this doesn't work I may go ahead and have them look at it and just deal with my wife being pissed at me for footing the bill.
 
#16 ·
Ok, pulled the carbs again today, disassembled (including jets/small parts) and soaked them for an hour or two while I changed the lower unit oil, changed spark plugs, put another 5gal of gas in the tank, then I went and fixed a couple of tires on my dads riding mower.

Used compressed air to blow out everything really well and then re-assembled and installed the carbs. She idles great now!

Thanks again to everyone. Hopefully Monday or Tuesday we'll be able to put her in the lake down the road and see if everything else is running good. Surprisingly all of the lights on the trailer were working good, I had to re-wire it the last time he used it, mice had chewed up the wiring.
 
#17 ·
Just a quick update:

Got it out on the water today, motor ran great. No excess oil consumption, no high rpm knock, plenty of power all the way to full throttle.

Thanks again to everyone, seeing my dad stick his cane into the fishing rod holder and open the throttle with an ear to ear grin was priceless.

Today was just a quick shakedown run, hopefully we'll hit the bay in a week or two.
 
#19 ·
If that wax pellet enricher gives you any trouble, pull it and freeze it for 12 hours, reinstall and it'll act fine for a few years.

Also, those things hate ethanol. run the blue shit from West Marine in it. It'll thank you for it.
 
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