Yamaha 250TXRR Problems

[BridgeTT]

Hi All,
I'm new here but not new to boating. I've been purchasing parts from boatsdotnet and stumbled across this forum. It seems like there's a lot of experienced Yamaha users and technicians here and I'm really hoping someone could give me some insight to some problems I've been experiencing with this 250TXRR Outboard. In a nutshell, here's what happened. I purchased a new Yamaha 150HP approx. 10 years ago after running away from old motor problems and that motor was sweet but got stolen. My boat have been parked up since and someone gave me what I thought was a steal of a deal by selling me a 250TXRR motor which sounded pretty good and powerful but I think I bounced my head. The motor only ran good once but I've been plagued by surging and bogging down issues. To me, the 150HP performed a lot better than this 250HP. This is the same reason why I ended up purchasing a new engine to get away from engine troubles, who wants an unreliable engine on a boat in open seas?
I might need to mention at this point that at first, I didn't know the engine was missing anything until I started troubleshooting. This engine was 'converted' to pre-mix in that it's missing all the oil injection components except for the main oil tank sensor. At the first sign of problems, I serviced the carbs. The engine had problems starting and idling, now that's gone but I never got back that power @ WOT. It was surging at some point and figured it's the low pressure fuel pumps but I decided to check out all other components. Now my tach was working with my new engine before but with this engine, it's dead so I'm not sure at what conditions are happening at what rpm. I read somewhere I could connect the tach directly to the green wire from the rectifier and I got a reading but when I increased the throttle, there was no increase in rpm on the tach. Also, when the engine was struggling at low rpms, I changed the plugs and it performed good for a brief period, then started doing the same thing. I'm basically getting 'trawling' speed. My boat used to do around 30-40mph with the new 150HP and I have patience but I'm not able to enjoy my boat and spending more time fixing than fishing. :faint2: I've gotten the seloc manual for this engine and I'm going through everything step by step but somehow I'm not getting anywhere. After I changed the plugs and got a momentary boost in performance, I checked the plugs and 3 of the 6 were wet. I assumed the ignition coils but checking each plug generated a spark. I'm not sure if it's weak but I don't know if someone can advise me if I'm going about this correctly. Here's what I've done:
Serviced carbs, tested TPS, synced carbs, set idle after setting TPS resistance. Tested temp switch (in case it's in some sort of safe mode), the main oil tank sensor is in the 'up' position (not sure if this sensor has something to do with not getting to higher rpms). I've changed the ignition coil ends (after seeing the wet plugs thinking is an ignition problem) and cleaned fuel filter. The O-rings on a few of the fuel enrichment solenoid were worn or damaged and I replaced them. What I'm going to do (after getting same results) is replace all 3 fuel pumps (as I was getting heavy smoke @ idle), replace the rectifier (as tach not working and getting a parasitic battery drain although the motor is generating good voltage 13.4-14v) and service the carbs again. Also going to clean out the fuel tank and replace fuel lines as the primer bulb does take awhile to get hard (maybe linked to the LPFP). Is there anything I'm missing or what advice do you all have? I have a sense of humor so let me have all suggestions. I've had three different technicians check this out, spent a lot of money and after getting the same result, here I am trying to fix this myself. One of the guys changed a coil under the flywheel (it looked like the smaller 'stator' coil but I don't know anything about these coils). I want to do some fishing ASAP! Thanks in advance for any suggestions and I wanted to be detailed, not lengthy.

Regards,
Watkin

 

[BridgeTT]

Just wanted to add a link to a video when it first performed alright. "https://www.youtube.com/watch?v=arM7_0S7wAI" At this point I'm thinking my Yamaha 150HP used to perform just as good! Where's the extra 100HP and this is at WOT. Not more than 15mins later, it started surging. Maybe I shouldn't have spoke bad of the motor, it has been misbehaving since.. :noidea:At first I was stumped and immediately ran it off of an external fuel tank to eliminate fuel restrictions. What do you think of this performance on a 28' Pirogue?

 

[frankjohnson]

Want to make sure what you have, sounds like you have a 1994 or 1995 L250 V76 engine with 6 individual carbs. If so start with a timming light to see where your timming is at an idle, if it is running arround 7 degrees before top dead center then your throttle position sensor, knock sensor or crank position sensor could be bad causing the ecu to default to cdi, but first things first. If timming is running about 4 degrees after top dead center you should be good. Watch the timming for a while to see if it jumps arround at times as you could have an intermittent problem. If this is not the V76 carbed engine 1994 or 1995 please discard is information.

 

[frankjohnson]

Forgot to mention that should be an L250 V76 2 cycle carbed engine if were talking about the same engine.

 

[BridgeTT]

Thanks for your reply Frankjohnson. It is a 1993 250 V76 engine based on the Seloc manual with 6 individual carbs. I will get a timing light and check at idle and let you know my results. I had changed the TPS based on one of the Techs recommendation and that's how I ended up synching the carbs, adjusting TPS and idle. Seeing that's it's 1993 but V76 carbed engine, your pointers are still relevant, right? What you thought of the video? Another boater asked me to check the prop as they found it was revving high opposed to how fast it was running. I ended up buying another prop but that didn't make a difference as I suspect other components are involved. Will let you know!

 

[frankjohnson]

Should still apply. On that engine the timming is controlled by the ecu with input from the three sensors. Also make sure your manual enrichment valve is closed and the enrichment fuel pump is running anytime the key is on, it will give about 5 lbs of pressure to the enrichment solenoids the ecu will open the solinoids as needed for cold start and some run conditions.

 

[BridgeTT]

Great @

Should still apply...

Will look at all mentioned and let you know. I checked the LPFP and two diaphragms were bad, awaiting new LPFP and will check with the timing light. Looks like I'll be :fish2: soon.. :biggrin1:

 

[frankjohnson]

That could be your main problem, the pumps work off intakes #1, #3 and #5. A bad diagram would causing flooding in 1, 3 or 5 depending on the ones that are bad and inturn cause a lean run on 2,4 or 6. Keep in mind that engine is a cross flow engine port side carbs feed starboard cylinders and starboard carbs feed port side cylinders. Hope that solves your issue. Let us know.

 

[BridgeTT]

Oh ok, cool @

A bad diagram would causing flooding in 1, 3 or 5

That would explain why the plugs that seem to getting wet is on one side of the engine. Can't wait to post an update but I'm still awaiting the parts. I ordered some gaskets along with the LPFP and that's on a back order. Hoping to get them by the end of the week. Will keep you posted!

 

[BridgeTT]

Good day,
I finally got the parts and installed the LPFP, changed the fuel filter and rectifier. Went through the carbs, changed O-rings for the fuel enrichment solenoids, synced the carbs, checked the TPS to make sure it was set (0.47v). Although the line in was 5v, I found the range topped out around 3.9v @ WOT, is that normal or the range on the TPS should be all the way up to 5v? When I started the engine and it was idling, I noticed two things: Still not getting the rpm on the tach and the engine wasn't 'peeing'. I checked the 'pee hole' to make sure it wasn't clogged, started again and same thing. I have a tank I test but I've used the 'ear muffs' before and not sure if any damage was done but I've always found the water coming out to be kind of weak. Throughout this test and the past few times, we used the tank so I'm not sure what's happening here. I dropped the lower unit and inspected the impeller. The impeller was in good condition. We put back up the lower unit, started her up and she began 'peeing' again but weak. We decided to take it for a run yesterday and at first, I thought the problem was solved as it pulled off quick but started to surge again shortly after. As we were coming back, although we have new LPFP, I decided to try pumping the primer bulb to see if it made a difference and I was shocked to see that it did after changing the LPFP. It revved up while pumping and bogged down with I stopped. I seem to still be having a fuel supply problem. I'm thinking that the carb might be running out of fuel and floats need re-adjusting. What are your thoughts on this? I also noticed another problem while running, :facepalm: to me, I find the engine has developed a 'knock'. This knocking sounds similar to a diesel engine rattle. What could cause this and would this throw off the knock sensor or is it in indication of a faulty knock sensor? I'm starting to wonder if I have the energy to tackle all of these problems. For one, the engine performed better than all the other times. After the initial run (first time we got the engine), we got a good speed, then we barely got above idling speed with all these issues. Now its running a little better but it's not even enough to plane the boat. If it's not one thing, its the other. Are these issues fixable? Please advise.

Regards,
Watkin

 

[frankjohnson]

Arround 4.2 volts is where I see most of them at wot. The knocking sound may be a bad knock sensor not changing advancing your timming for best detention, a timming lite will show this, if timming dropes back to before tdc the knock sensor is bad. Make sure your electric enrichment pump is running pumping fuel anytime key is on. Make sure manual enrichment valve is closed. Make sure the enrichment solinoid orings aren't leaking by, check that by tilting engine forwsrd, squeeze primmer ball till its firm, turn key on not starting engine, wait a minute or so and squeeze primer ball agsin if it is no longer firm watch for fuel running out of any carb. You do have a fuel delivery issue. Do you have good even compression? You have to have crankcase pressure and vacume to make the fuel pumps work, if you have low compression on the plug side then you will have low compression and vacume on the back side not letting the fuel pumps work as the should. Most anything is fixable depending on how much time and money you want to put in it. But check your compression first, run engine untill it warms up, remove all plugs, open throttle wide open, then check each cylinder with a few spins of the engine on each cylinder. I hope some of this helps.

 

[BridgeTT]

Ok @ All. I wonder what difference .3v would make @ WOT? It seems like I really need to know how the engine timing is doing. I checked all the solenoid O-rings and replaced them. With the ignition key on, it's not leaking anymore. Before I replaced the parts, 2 of the carbs were leaking. Compression seem to be ok:noidea: #1-105psi; #2-95psi; #3-105psi; #4-105psi; #5-110psi & #6-110psi. The thing is, the knocking is so noticeable now at idle.. Yet it idles so nicely, no hesitation or misses. From a cold start, it idles up, then bubbles back down to a comfortable, consistent idle which correct me if I'm wrong, indicates the engine is recognizing various conditions and adjusting itself. I guess only the timing light might indicate. Considering compression more or less above 100psi and the knock sensor tested ok based on seloc manual as did the crank position sensor; do crankshaft bearings go and contribute to this knock? I will run through and address all fuel related concerns. Let me see if I could give this thing one last try. Thanks so far, it seems like you're the Yamaha guru on this forum. :becky: Will keep you posted.

 

[frankjohnson]

Not really the mine run .51 at closed throttle to 4.02 at wot. So your within it's operating range on your tps. Im no guru just have to keep my V76 engines running so I learned a lot about them, they are a unique engine.

 

[frankjohnson]

If your timming is holding and being advanced not falling back before tdc the knock may not be an issue. The knock sensors job is to detect the ignition knock and adjust the timming to correct it. It won't help if there is an internal problem like crank or rod bearings going bad.