yamaha 50TLR can't get past 4200RPM

srantheman

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I purchased a G3 16ft pontoon boat earlier this year with a yamaha 50TLR on it. Part number on motor is 50TLR 6h5k 1030341F. When I bought the boat, I replaced the fuel tank, fuel lines, and spark plugs. Boat run great the first couple of times I took it out. A couple of weeks ago the motor flooded and wouldn't start back. I got it home let it sit that day and then it cranked the next day. Since then it will crank fine, idle fine, but at WOT it will only get to 4200RPM. It also seems to be running really rich. I'm wondering if the prime start feature is stuck on and that is causing the system to be rich. I'm going to try the next time we go out to turn that feature off since it's the summer time. Is there anything else I should be checking? I would take it to a boat shop but all of them in my area are 4-5 weeks before any of them can look at it. Any help would be greatly appreciated.
 

Sea Rider

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Welcome to IBoats,

At which max wot rpm was the motor running previously before achieving poor rpm numbers ?

Happy Boating
 

srantheman

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Max rpm on the boat is 5000-5200rpm and 20mph. I’m now getting 4000-42000rpm and 15mph. I haven’t tried to run the boat with anything off of it. My next step was to eliminate the prime start by turning that off to take that out of the equation. I’m open to any and all suggestions to try and get this figured out.
 

Sea Rider

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Some tech issues :

Was the motor previously revving around 5000-5200 while doing 20 MPH ?
Is that the max wot rpm range factory stated or the max rev the motor was revving at ?
Would you say was a gradual rpm loss or from one day to the other ?
Does the motor revs evenly throughout the whole throttle range or misses, hesitates, bogs at some point ?
Is it a 2 or 4 stroke motor, which year or how old is it ?

That motor should wot rev at : 5000-5500, 5500-6000 or 5000-6000, do you know which is min-max rpm factory stated ?

Something is way wrong to achieve just 20 MPH with a 50 HP horse, my 2 stroke 18 HP Tohatsu runs bit more than 20 MPH with 2 up. If all is good seems a prop issue, could be on its way to become fully spun ?

Happy Boating
 

JimS123

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5200 should be about optimum for that motor. Since its a toon 20 mph is probably in the range. The other thing to look at is the oil injection system. If you can disable it and run 50:1 pre-mix without it running "rich", that could be a source of your problem. A spark plug check will verify that. If 2 are good and the third is oily, you may be running on only 2 cylinders.
 

srantheman

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Manufacturers spec is 5000-5500 range. It’s a 2010 16 foot pontoon so 20mph with 2 adults and 2 kids plus gear I say is about normal.

It’s pretty smooth rpms all the way through the throttle. It just never tops out like it used to.

spark plugs all look evenly burnt and none of them are oily or wet when done running.

Is there an easy way to disable the oil injection? Do I have to take the oil reservoir off or can I just unplug it? First boat I have ever owned to have it. Previous boats just mixed in the tank. I have included pictures of new spark plugs that were taken off after 5-6 times on the lake. Each trip we average 2-3 gallons of gas. I hope this helps you guys out.
 

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JimS123

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The plugs look OK. If the oil system were suspect, they wouldn't look like that. Did you check all 3?

If it were a spun prop you wouldn't get speed, but my guess is that the rpm would still go high.

I still say you may have lost one cylinder. At idle, pull off the plug wires one at a time. If you pull one and nothing happens you'll know which one is not running.
 

srantheman

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So all 3 plugs looked exactly the same. I replaced them all to see if that made any difference. I’ll run it at idle tonight and pull the new plugs and make sure all of them are firing. I’ll send new pictures of all 3 plugs tonight.
 

srantheman

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So this is what I did tonight. I took the spark plugs out, cleaned them with carb cleaner and took the pictures. i then cranked the motor and let it run for 1 minute and took the plugs out and then took pictures of the plugs. I labeled the after pictures of what cylinder they came out of in case there was a problem cylinder. I don't think I have a dead cylinder as all of the plugs look about the same. I have a video of it running and can upload it if you think that will help at all. It runs really smooth at idle.
 

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tblshur

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just a thought have u tried pumping the bulb when it gets to 4200
 

srantheman

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I haven't tried that. it is on my list for when I can get to the lake this week. I'm about 45 minutes away from the nearest lake so i can only get down there a couple of times a week.
 

Sea Rider

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Would be surprised the strange prop behavior produced when the hub is on its way to become fully spun, props spuns gradually, have had 3 same issues with different HP outboards. Check that all carbs are opening fully and perform a prop hub slip test to rule out it's not a prop issue, leave spark plugs alone which are firing as it should for 2 stroke OB's.

If the prop is found to be shot, will be replaced by current same or at least one less prop pitch for motor to rev to its max wot rpm range assuming that with current one didn't achieve max wot rpm ?

Happy Boating
 

srantheman

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I was able to get to the lake yesterday afternoon. Below are what I did. Each test was done from motor off and done individually. I have also included a link to a video I took from idle speed to WOT. The motor did hestitate but did get to 4200RPM.



1. Set Prime Start lever to off - didn't change motor performance or starting procedure.
2. Took Gas tank cap off to increase air flow - Didn't change motor performance
3. Squeeze prime bulb once we get to WOT - Bulb was very firm and hard to squeeze. What I was able to squeeze didn't lower or raise the RPM of the boat.
4. Trim Motor up to level out the motor - Made the boat run smoother on the water but still topped out at 4200RPM

The motor did smoke quite a bit at first but i don't feel it was an extremely excessive amount.
 

JimS123

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Its hard to diagnose remote control. With that caveat, I can only comment on "feelings".

I saw a lot of water in the bilge. Is the boat full of water and you are struggling because of excess weight?

The engine "sounded" like it was laboring. Just like in my past when i lost a cylinder. Hate to repeat myself, but I'd leave the cowl off and pull plug wires one at a time.

I'll leave this question for the other aficionados since I never experienced a spun prop first hand........if a prop is spun, do you get higher or lower rpms at WOT?
 

Sea Rider

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A matter to know if other highly aficionados have experienced so ? Do you think that a prop will go wrong from one day to the other of from one hour to the other ? Seen same issue with 5, 40, 70 HP motor props to speak about.

The issue here that it's way faster to take the prop off, mark it, put it back, go for a wot spin as currently were loaded, take it off again and check if the marks or straight line has moved from where original were marked from or keep wild guessing what's wrong while losing precious boating time. Also check as recommended if the hull is waterlogged adding extra hull weight. ?

The OP stated on his last outing that the motor run smoother but at same 4200 wot rom, so how could that motor be running smoothly with one cylinder down. If suspect rule it out with a spark plug tester to check if all spark plugs fires healthy, if so, the next step is to do a cylinder compression test. Good Luck !!

Happy Boating
 

srantheman

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I do understand that is it hard to diagnose remotely. I also appreciate all the feelings and ideas people have had about this problem.

If I didn’t mention in my earlier post, I did run the boat at idle and remove each wire off plug. Every wire acted exactly the same. The motor started to miss when removed.

As for the water around the motor, this is a pontoon and that area is open to the water. It just has a protective metal housing around it.

As for weight, my boat is rated for a maximum 6 people and 1200 pounds. When we did this test, it was just me and my friend and a few fishing rods.

As for the spun prop, I would think it would act like a slipping transmission in a car and you would lose power but gain RPM.

On the last note, the boat is going to a mechanic after this weekend for him to verify the carbs are correct and see if he can determine the issue. Once I hear back from him, I will be more than happy to post the results. Maybe it will help somebody down the road.
 

srantheman

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I got the boat back today from the shop today. The diagnosis was that the choke was stuck on. He didn't elaborate if that was the prime start stuck on or if the butterfly was staying closed. Either way the boat is running like it should in the shop and we are going to do a water test Friday or Saturday. Hopefully this helps anybody that is having the same issue. We did try moving the red switch but it didn't actually do anything. Just wanted to post this out there for anybody that is having a similar issue.

Thanks again for all of your help.
 

Sea Rider

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All rotating/sliding carb parts shoul be oiled periodically so no part gets half or full stuck, have never had such problems, usually micro oil all my motor's carbs and their throttle system periodically for a smooth operation...

Happy Boating
 

JimS123

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I got the boat back today from the shop today. The diagnosis was that the choke was stuck on. He didn't elaborate if that was the prime start stuck on or if the butterfly was staying closed. Either way the boat is running like it should in the shop and we are going to do a water test Friday or Saturday. Hopefully this helps anybody that is having the same issue. We did try moving the red switch but it didn't actually do anything. Just wanted to post this out there for anybody that is having a similar issue.

Thanks again for all of your help.

I'm trying to take this with a grain of salt. In the olden days (my youth) before i knew what's what I would rely on a local cheap mechanic to tune up my boat. The last time he did he didn't lube the choke and I had problems. Then I went to the libary and got a book and learned to do it myself.

The point is that when I've had a sticking choke, she blew back smoke and you REALLY knew there was a problem. Not that it couldn't reach rpm, but it ran crappy at all angles.

I don't believe your mechanic. I hope I'm wrong and your boat runs like new now, but if it doesn't who am I to say.

Anxiously awaiting your sea trial...
 
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