Newer Yamaha 50 HP 4-stroke question

[outbdnut2]

No chokes. It has an electric primer – part #34 in link below. Also – I must be remembering it wrong as a 4 cylinder. Parts list shows 3 cylinders, 3 carbs, so maybe it’s runnin’ on 2 of the 3 cylinders. I notice each carb has a different part number – interesting!.

Here’s a link to exploded view of carb parts: https://shop.yamahaonlineparts.com/OEMpartfinder.htm#/Yamaha_Outboard/50TLRC_-_2004/CARBURETOR/ca86f2bb-ecd3-4be4-8622-337eac184d69/8f531dd5-ab24-423b-acdf-10d1574f6de4/y

I been thinking about it more and If a cylinder is dead, I can find the dead one by starting it with different spark plug wires disconnected and see which one makes no difference in how it runs at idle. I’ll be doing this out of water with garden hose clamped to cooling intake. I may also notice that one spark plug stays cold. When removed, one plug may be wet. I also have a seldom used in-line neon spark flasher/indicator I can put between the spark plug and its wire. If the sun isn’t too bright, I will see the neon bulb flash if there is spark voltage.

I also plan on a look at the throttle linkage to see if some adjustable part (if any) has come loose, preventing carbs and/or spark advance from going to max., or maybe one carb has throttle disconnected, if that’s possible.

It’s a tiller motor, so easy to advance throttle and see what moves….to a point – the intake cowl on the carbs blocks view of some stuff. I seem to remember it has cables going in from the tiller – maybe something slipped inthe throttle cable causing it to not go to WOT.

If I start it with a spark plug wire off, do I have to ground it to keep ignition parts from self-destructing?

Dave

• This reply was modified 4 years, 5 months ago by outbdnut2.

[billw]

Grounding the spark plug leads or at least through some kind of spark checker is highly recommended. As they always say, electricity is lazy. If there is too big a gap for the spark to jump, it will eventually find an easier path through the insulation in the coil winding, someplace. Japanese ignition parts are absolutely as good as it gets, but nothing is THAT good, for long.

Does the owner report that it stalls at low speeds? If not, I am thinking your garden hose test may not show anything but three running cylinders…..

Very wise move to observe the throttle action before doing anything as rash as a carb job on that thing.

Don’t forget that the “fuel system” includes the tank and line! One time, I saw a Yamaha that idled well and would run mid-range just fine; but it wouldn’t go fast. The owner had attached the fuel line to the tank backwards. At low speed, there was enough fuel getting by the backwards primer ball valves to keep running! I have also seen many plastic tanks, that have a plastic withdrawal tube. The ethanol damages the tube, which causes air to leak into the system at the top of the tube. That could definitely cause high speed problems. remember that trouble shooting is a matter of “divide and conquer.” It would be best to take a ride with an entirely different, known-good tank and line and see if he gets a different result in speed.

Long live American manufacturing!

• This reply was modified 4 years, 5 months ago by billw.
• This reply was modified 4 years, 5 months ago by billw.

[outbdnut2]

Thanks for the tank reminder. His fuel tank is factory built-in under the floor of his 16′ Lund fishing boat so no chance of the fuel line being reversed, but, good idea – I could take the tank from my 25 HP Yamaha 4-stroke on my pontoon and try it. He hasn’t mentioned stalling at low speeds. He does have a lake one mile from his house, so we could drop it in so I can see how it runs at high throttle if I can’t figure it out in his driveway. He uses 10% ethanol gas due to limited availability of ethanol-free where he lives, so that could have created a problem over its 16 years..

I once cobbled in my Yamaha tank to the MerCruiser inboad/outbaord engine in my ski boat when it would bog at sustained high speeds, and it ran fine on the Yamaha tank. I found the anti-syphon check valve was bad with it’s spring broken and jammed up. A couple weeks later, same symptom, and ran on the temporary tank OK. This time it was the pickup screen in the built-in tank clogged with crud that somehow got in there.
Dave

[outbdnut2]

I took a look at this motor and found #2 spark plug was somewhat wet with gas after having not been run for about 10 days. The other three plugs looked good. All throttle/carb linkage checked out OK. I replaced the wet plug with an old plug that looked good. Before putting it in, I grounded it and cranked and it had healthy spark in its gap (I didn’t have a way with me of looking for a longer spark in free air). It seemed to idle OK , but this was all I could do in the driveway. The next day, my friend took it to a lake and it still would only go about 3/4 speed. Based on all this, I suspect #2 cylinder’s carb has a problem. He dropped it off at a dealer Saturday. I’ll let you know when I hear what they find. I’ve never been afraid of carbs on cars or motors, but my friend is a particular guy and I didn’t want to be learning these carbs on his motor.
Dave

[billw]

If he is a particular guy, I would have him get a newer engine with EFI. MUCH more reliable than a carb 4-stroke. Carbs are going to be nothing but problems for him and costly to have repaired professionally.

Long live American manufacturing!

[outbdnut2]

Good thought – an efi motor would be good reliability, and he takes it a couple times a year into the “Boonies” in Canada for a week or two at a time. I think he’s been lucky with this carb motor so far because he bought this 2004 new and this is the first problem he’s had with it, other than ordinary maintenance – spark plugs and oil changes.
Dave

[billw]

He has been unbelievably lucky. Without reading this whole thread again, does he use non-ethanol fuel, or something? Some owners of engines of that vintage have carb problems almost every single year.

Long live American manufacturing!

[outbdnut2]

He uses 10% ethanol fuel because that is what’s available near his house. When winter comes, he adds a can of Seafoam to his 20 gallon boat tank, which is vented to the atmosphere like most all boat tanks, but he doesn’t add any other stabilizer. I’m amazed this has worked for him in unheated storage in Minnesota. I would expect some phase separation when the temp drops. Maybe the Seafoam somehow keeps the ethanol from absorbing humidity from the air like Stabil-Marine does?

Dave

[outbdnut2]

A quick update: He took this in to what is probably the largest marine dealer in Minnesota, and when he got it back, it still wasn’t right. I haven’t heard what they did to it. He has it back in their shop again.

The place where he bought it new in 2004 said they don’t work on motors that old. Stay tuned……..
Dave

[outbdnut2]

Ok – here’s the end of the story. First time in to the dealer, they put a new fuel line with primer bulb on his 2004 Lund boat that has tank under the floor (I remember the primer bulb was getting marginal, felt like check valve was leaking some); installed a new battery, and checked out the motor (not sure if they did anything to it) but no new parts in it. Cost = $600. Still didn’t fix the problem. 2nd time in, told him it would cost $1,600 for carb work (maybe that’s 4 new carbs? At Crowley Marine online the 4 carbs range form $200 to $400 each depending on which carb). He traded it on a new, injected Yamaha 50 for around $6k.

You guys were right about the Yamaha carbs on that model! I’m glad I didn’t get involved tearing into them and learning on his motor!
Dave

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