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YBR 250 (09, Fuel Injected) - Black Smoke - Engine done?

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raystone
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PostPosted: 00:04 - 18 Jun 2017    Post subject: YBR 250 (09, Fuel Injected) - Black Smoke - Engine done? Reply with quote

I am begging (and I mean it), for anyone's help here.

My girlfriend just got back into biking, and we bought her a (rare in the UK) YBR 250 (fuel-injected!). It's already got 40k miles on it, but is in pristine optical condition. Previous owner changed oil, oil filter, and battery — also claims to have had the bike in a garage (saw it in there) for almost a year.

The bike idles perfectly calm at 1500, sounds smooth.

Worked a treat for a few days, then we noticed considerable jumping/jerking back and forth when riding it, holding the throttle perfectly still, it started to get very unpleasant to ride.

I inspected spark plug — sooty, very black, dusty. Exhaust has fuel smell, so it's definitely running rich. Then I inspected the air filter, while not super clean, it's also not the problem (I removed it, rode the thing around for a while without it, same issue, unchanged — also talked to mechanic about it, he said it's dirty, but not anywhere near problematic). Replaced the spark plug with a brand new one (correct one).

Today, it got even worse. While riding 30mph, the engine just stalled mid-run. Gone. Managed to restart on the go, died a few later, so I high-trottled it to a mechanic nearby, barely made it. Showed him the thing, and he revved it up like crazy (over the limits) — black smoke coming out (didn't notice any black smoke in lower revs). But higher revs did not look good at all.

He then ran it up and down the street (rode it really, really hard) and came back with bad news. He says this is terminal, the engine (top end) is done for. Now, normally I'd be cautious, but I usually trust those guys. He says it could be fixed, but not really as the YBR 250 is so rare, it'll be impossible to get all the parts, and it'll cost a lot of money likely.

So, I beg for any other comment and he says I should try and ride it hard, really hard for a bit and see if that improves things. If it does, then I'm good, otherwise, engine is done.

I ride the thing really hard for half an hour, and almost feel like it may be improving a bit, but then it dies. And it dies hard. Could not get it back to start again (waited a while, gave fuel pump time to prime and all, nothing). Side of the street, get out the spark plug, clean it up (sooty again), put it back in — kicks in and runs again. I ride it home in high-trottle, but barely so. That's the status.

Battery was changed three weeks ago to a brand-new one. Measured it, all seems fine, even under starting load.

I go online to research, and everybody seems to say it's either the TPS, or faulty wiring (ground issues) on the YBR, or rubbish in the fuel tank. Lots of Spanish posts on YouTube (bike was big in Brasil), a lot of them talking about issues mentioned above.

Fuel tank — I put in some Renex (one quarter of a bottle) yesterday, then re-fueled with premium petrol.

What do the pros say, engine done for? Black smoke on high revs and rich fuel mix.

I don't have a Yamaha FI Diagnostics tool, and I'm sure it would help measure the TPS (tried to get at the wires last night, no chance). But I know my way around electronics, and I can measure. Problem is the only way to get to the wires is through the ECU plug, but that means ECU unplugged, no supplying the volts to get a reading from the TPS pins.

Also, I checked engine oil yesterday, and it seemed to be running low, so I filled that up again as well without noticing any changes.

Ugh. Help — my girlfriend was so happy with this thing, and it barely lasted us a week and she's ready to just throw in the towel and give up. I depend on you!
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temeluchus
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PostPosted: 00:24 - 18 Jun 2017    Post subject: Reply with quote

The injector could be clagged up, if it can't close again it will run rich as buggery.
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raystone
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PostPosted: 00:42 - 18 Jun 2017    Post subject: Reply with quote

interesting — here I was, thinking that a clogged injector won't be the issue, as it's getting too much fuel if anything — so it barely can be clogged. But didn't think of it that way — would the Redex thing help with that?
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Teflon-Mike
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PostPosted: 01:45 - 18 Jun 2017    Post subject: Reply with quote

raystone wrote:
interesting — here I was, thinking that a clogged injector won't be the issue, as it's getting too much fuel if anything — so it barely can be clogged. But didn't think of it that way — would the Redex thing help with that?

This is why I like carbs. However.
White Smoke = Water (unlikely o an air-cooled Engine)
Blue Smoke = Oil
Black Smoke = Fuel

However, Your mechanic's reported diagnostics sounds a tad suss to me; could be repetition distortion, but if a 'top-end' is 'terminal', then I would expect the cam-chain to be rattling in the gallery, the cam to be clattering in it's bearings, and for tappet to be making a noise like all the Dwarves of the Hobbit preparing for the last battle! And lots and lots of BLUE smoke from oil going down the guides.

Its an air-cooled OHC single; of not particularly ancient vintage; a head-gasket fail, wouldn't show as white smoke, or coolant loss, would only show up under load or compression test.. which is another check I would do, and am surprised a mechanic didn't, before suggesting a termnat top end! Were they a bike mechanic or a car garage? A potter round the block and a proouncement like that, sounds like an "I dont want to really touch this, I'd like the fella to just take it away, but I would like his other business still" sluff off.

Top end fail isn't utterly off the cards, would take the thng t have been run without sufficient engine oil, for a while, and as said,would manifest itself by blue smoke o the over-run and or acceleration, and lots of elvish black-smith sounds; not poor carburation and obviouse over-fueling!

VERY VERY stupid idea.. but has some-one done the dum and stuck deseasil in the thing at some point? Could be worth draining the tank, and putting in a gallon or so of fresh; then, I'm not familiar with the YBR EFI, but on a car, I'd pop the fuel rail return line and vent into an old oil bottle, and then turn the ignition on, and let the pump 'prime' and clear the lines, until I'd got maybe a liter of fuel 'purged'. If there's a high-pressure i-line fuel filter in there, I might swap that out too. Could be worth a try.

Injectors dont like being left sat derelict for very long; and will gum-up. I have very very little faith in redex type tank treatments; in the 1960's when engines tended to run a bit sooty and tolerances meant they almost all burned a bit of engine oil, and demanded 'De-Cokes' as a routine service op, there was some justification for now and again, but even there; didn't exactly remove the need to de-coke, just pushed out the intervals a bit, and most oft used to mask a very tired motor well beyond 'just' needing a de-coke! Modern injector cleaner fuel additives, do seem to have more actual effect ad use; and this COULD be a case where one may be appropriate to maybe clean up a sticky syringe, that isn't too far gone or worn out.... but, I'm still a cynic, and see far too many use such brews as a placebo or peril-sensitive sunglasses to dodge a real spanner issue.

The Throttle-Position-Sensor is I believe a known issue o these; its a carbon track potentiometer, and prone to getting a bit crudded up and sending false sgnatls. Aught be reasonaly easy to pop it, and clean it, or maybe douse in aerosol solvent cleaner, and work back and forth to clean up the track and contacts.

I don't know, but would expect the YBR EFI to be a closed loop system with an O2 sensor in the exhaust pipe; once the motor is started, and off the cold-start circuit, that should start to tell the EFI 'brain' what to do with the mixture, rather than it using a default 'limp home' map...

If the bikes been sat, and has been run up on cold start and not gve a good thrash, possible that the exhaust sensor is dirty or duff; again might be pulled and cleaned, & I believe that they can be tested with a mult-meter.

I would expect, if the EFI isn't getting a decent lambda sensor signal though, that a blink code of some-sort would be given on the dash panel... do you have the ower's book? Could be worth a look in there, AND at the dash panel.... not unknown for folk to pull dash lamps that give blink-code warnings, either to get a vehicle through MOT or sell on....

Gross over-fueling could be caused by a hole in the exhaust or a missing exhaust gasket, if sensor is good, so would have a check for obviouse exhaust faults....

Cold-Start circuit would also tend to be triggerd by a temp sensor; that too could cause gross over-fuel, like always running with the choke on; When does the brain get its temp data from? Is it conected? Look for loose or broken wires around electrik 'things' on the engine!

Lack of a computer interface to interrogate the brain? Yeah... we live in the digital age; people do seem to like looking at lap-tops rather than bits of actual metal... but, end of the day, the brain only knows what signals it aught to get, it doesn't know whether if it's not getting them,why, and as said, most of what a brain might tell a lap top, it will usually tell a blink code lamp... and what a lap-top might elaborate on, would probably be greek to me anyway! And you can go an awful long way with a little common sense, simple logic ad some old fashioned proddig and poking, i the right-places, so I wouldn't be uduly worried about that one.

But as any starting point; I would try ad eliminate the dum variables first; and do a basic service as per the book, by way of new plug; tickle the tappets, tweek the CCT; do an oil change, look for the obviouse around wires going to the engine, around the exhaust, and that desesil/condensation/crud purge fro the petrol tank; then probably give it a good thrashing; to blow out the cob-webs, get some fuel through the lines and squirty thing; get the motor propper warm, and give the ECU a chace to re-calibrate itself; so, no short shifting, gingerig the thig; out of town, all the revs in every gear, kill-or-cure over mechanical sympathy, for half an hour or so (With AA card i my pocket with the cell-pohone!) THEN re-evaluate what you got.

IF that didn't get you anywhere; then a franchise Yamaha dealer, with the proper interface to plug into one of these, and possibly more inclination to do something and take your money for it, rather than just take a joy-ride, is probably a lot cheaper and likely to tell you something 'useful' and more reliable, than a chinky lap-top interface to get the greek out the brain, or a back-street bodger, possibly out of their comfort zone... so that would probably be the last ditch, crack out the credit card and bite the bullet, solution... and if THEY said the top end was terminal, might be a little more inclined to believe them, in the absence of elvish sword smiths taking up residence in the rocker cover!
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temeluchus
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PostPosted: 18:21 - 18 Jun 2017    Post subject: Reply with quote

raystone wrote:
interesting — here I was, thinking that a clogged injector won't be the issue, as it's getting too much fuel if anything — so it barely can be clogged. But didn't think of it that way — would the Redex thing help with that?


They can get some gunk in, corrode and jam open. If everything else checks out, it's an easy thing to change. Might be possible to pick up an injector for next to nothing.
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raystone
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PostPosted: 23:10 - 18 Jun 2017    Post subject: Reply with quote

I'm back with the bike in the morning, and I'll try to check every single one of your recommendations. They all sound very, very promising — but I'll know more when I get to it. Too bad I don't have the Yamaha FI Diagnostics tool, would've been super easy to get the TPS readings at least. But well, I'll retry with the multimeter then.

Will also disconnect the entire throttle body to get the fuel injector, hopefully there's a way to see what the status is.

Thanks again guys (especially Teflon-Mike, for that super detailed write-up!), I will report back — if anyone else have runs into the same issue on this odd thing of a bike, they will find the answer at the end of this.
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raystone
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PostPosted: 11:44 - 20 Jun 2017    Post subject: Reply with quote

Just wanted to follow-up on this, and not be like all those other posts where the issue get resolved but we never hear about it.

Yesterday, I spent two hours to get the entire throttle body out of the bike, and I cleaned it up really well. This gave me a chance to measure the TPS, which is part of a hybrid/multi-sensor on the YBR 250. The TPS looked fine, applied a 9V and rotated evenly, measurements were accordingly smooth. Good, and bad. This eliminates the TPS as a potential issue, but it also means I have to look further.

I then tested the temperature sensor, which is located at the engine side of the throttle body, and it gave me stable readings (cooled it, heated it a little) and it went up and resettled. Not sure what the voltage/temperature table is, couldn't find a service manual in English for the YBR 250 (just Spanish ones).

Then, I attached a hose to a can of carb cleaner/air-intake cleaner (which is mostly petrol I think), and to the fuel injector on the throttle body. I added a 9V battery that allowed me to tap the contacts on the fuel injector to open the valve, and started spraying/opening the valve a couple of times. Amazing thing to do, if you're mechanically interested.

I also cleaned the fuel injector contacts (openings, looked like 6 tiny dots or so) and sprayed electrical contact cleaner on all the contact cables of the throttle body. I removed a lot of the grime from the trottle spring, and the entire thing looked almost brand-new.

Then I re-fitted it back into the bike, which made me promise myself to never take that beast out of there again (there's barely any room to fit it back into the engine- as well as air-intake pipes. Did not feel nice, but worked after a long while of wiggling around.

Re-connected everything, cleaned the spark-plug once more and fired it up.

Smooth as f***. Lovely.

I rode it around the block a bit, and it felt immediately better. I did notice a bit of lag/jumping here and there, but by far, far not as much as it did two days ago.

Main difference other than cleaning was that when I rode it around, it was night-time. And the jumping/jerking back and forth was right bang at noon on one of London's rare 30 degree celsius days.

Today is another such tremendously hot day, so I'll try to get that thing back on the road and see if there's any more issues with it when it's heated up.

If that's not resolving it, my next steps will/would be:

a) check o2 sensor and see if its resistance is okay

b) check for potential air-leaks that may hinder compression (not entirely sure how? can I spray it with water or something and see bubbles?)

c) clean out tank entirely (not sure where to dump almost 18L of petrol), and possibly take out fuel pump to see if there's any noticeable issues with it.

Other than that, no idea what else to check. But I'll know more after today. If you don't hear from me again, then thanks and it may hopefully help some of the other 294 registered YBR 250 owners in all of the UK (next time, I'll check for that first).

I had severe/similar issues with a Yamaha scooter (Vity 125), and ordered a replacement fuel pump off eBay. That worked out quite nicely and solved the issue for the scooter. But people then said there were faulty pumps, so it seemed worth a try. Honda CBF 125 seem to have extreme issues with the fuel pump (and the gas tank coating when new), but I haven't read anything about the YBR 250 on that.
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raystone
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PostPosted: 23:42 - 20 Jun 2017    Post subject: Reply with quote

... and I'm back with the next issue.

Bike ran perfect with the cleaned throttle body. Until I parked it up in the sun and returned an hour later.

Fuel pump does not prime anymore (I remembered this issue from a Yamaha Scooter), so I pushed it into the shadow and waited.

35 minutes later, it had cooled down enough and the fuel pump started priming again. It's the same fuel pump issue that exists in almost every single YBR 125, Yamaha Vity and lots of smaller Yamaha's (and Hondas) in the 50cc to 250cc range. SUCKS!

Ordered a new fuel pump on eBay, so that will hopefully solve that. I still wonder what exactly (like in detail) the fuel pump is so upset about. Heat means something expands, so I opened up the engine by taking out the spark plug, just in case it was overly compressed from that end, for whatever reason, then re-fit and tried again. Same result.

Really needed a severe drop of temperature until it primed again. Engine light and everything else looks identical, just the priming does not happen (you can almost notice a tiny little bit of it trying but it gives up immediately).

Weird, weird, weird.
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stevo as b4
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PostPosted: 18:07 - 21 Jun 2017    Post subject: Reply with quote

Looking promising hopefully!

Almost makes you want to take the engine out and throw it in the so called mechanics face, using the throttle body to perform dental surgery on him, for thrashing the shit out of your bike, and then telling you it probably has a fucked engine?

Which school of motorcycle mechanics did this Einstein come from exactly?
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Chris45
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PostPosted: 20:40 - 21 Jun 2017    Post subject: Reply with quote

Have you tried changing the girlfriend?

Honestly m8, the bike sounds a fooking nightmare. Even on a really hot day, an engine should start no problem. Went to Aviemore two weeks back, it was absolutely sweltering and my bike was sitting in the heat for over two hours (gpz500 twin carbs). Fired into life on the first press of the button and I didn't expect anything less.
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raystone
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PostPosted: 20:41 - 21 Jun 2017    Post subject: Reply with quote

Oh yeah, trust me, I'm mad. If that motorcycle continues to run as expected for the remainder of the year, then I'm more than just a little pissed. I trusted those guys, a lot! For the past few years, I kept telling everyone how I always expect to be ripped off in London, and that must've been an impossible strike of luck that I found a shop I could trust. Makes me reconsider things quite a bit.

Probably varies from shop to shop, everyone's in it for a different quick buck it seems. Some just want to swap tyres and do MOTs, others may be more open to longer-term projects like engine rebuilds but not have an MOT license/facility.

Still taken aback a bit by the harsh diagnosis, and the fact that the bike runs smoothly now (minus the fuel pump in the sun thing).

Also asked for a quote in West London today, to see how much they'd charge if I bring by the fuel pump and bike at a convenient time. Just to save myself the hassle of flipping the tank around and replacing the pump — well, a £150, at least, two hours labour. Now, I'm a god-damn rookie, but I'll be timing my fuel-pump replacement tomorrow and something says even I can probably beat that time. Ugh.

Just saw another poor soul a few threads up complain about his YBR 125 and the sun. Fuel pumps mate, what a waste.
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raystone
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PostPosted: 23:53 - 21 Jun 2017    Post subject: Reply with quote

Chris45 wrote:
Have you tried changing the girlfriend?


Well, I tried, but your mum hasn't called back in a while Cool
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raystone
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PostPosted: 17:21 - 23 Jun 2017    Post subject: Reply with quote

Help! I'm now back at the start, same shit issues.

I've replaced: air filter, oil, oil filter, spark plug (twice), fuel with premium fuel (ran one tank with Redex), and also replaced the fuel pump (and filter) now.

The bike idles okay, but once I start riding, it jumps/jerks violently (unable to ride longer distances at all), and it's gotten severely worse now. This starts happening in 1st gear already. It's nothing to do with the chain/sprockets, nothing mechanical. This purely sounds/feels/smells like a fuel issues (it's a fuel injected bike).

It feels like the bike is choking, but it doesn't really stall, once I put it into neutral and stay for a second on the spot, it idles okay.

As said, throttle body was taken out and cleaned, fuel injector valve was also cleaned. TPS sensor measured, and it checked out fine. After the throttle body clean, the bike seemed to run fine again (I'd say the jumping was barely noticeable, but nothing I'd worry about).

But a few days later now, it's all back to the same shit. I had a quick look inside the tank from the bottom side (when replacing the fuel pump) and it looked fine inside, no rust.

I am out of ideas. Can you help? I've spent so much time, and money, to sort this out, and it's all done exactly nothing.
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Nb
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PostPosted: 20:27 - 23 Jun 2017    Post subject: Reply with quote

I'd be looking into how the lambda sensor is working, is it switching at the correct voltage?
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raystone
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PostPosted: 20:40 - 23 Jun 2017    Post subject: Reply with quote

Haven't tested that one yet, do they go bad? OEM replacements are over 140 pounds, so phew.

Should be easily accessible on the exhaust to measure, I remember seeing it stuck in there. Do I take it out and measure off the bike? Or should I idle the engine and take some resistance readings? I'll do a bit of research to see how to measure this best, but I'll take a look at it. Thanks.

Any other ideas welcome.
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331X2
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PostPosted: 20:02 - 24 Jun 2017    Post subject: Reply with quote

Is it definitely fuel related and not ignition? Does it start acting the twat under load or is it at idle too?

Have you tried a tighter gap on the plug in case the spark is breaking down? Also is the HT lead moulded into the coil/plug cap or can if be removed to see if the cores have broken away?

Please ignore if you've been through this but I've been bit on the arse with more electrical problems than fuel in my short time playing with bikes Laughing
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raystone
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PostPosted: 10:50 - 25 Jun 2017    Post subject: Reply with quote

Well, with fuel injection, it's always a bit hard to know exactly what causes the ECU to decide it needs to richen up — but it definitely does that.

I checked the spark plug cap, and it was super duper clean, I sprayed some WD 40 in there, cleaned it out, then also some electrical contact cleaner.

The bike idles perfectly fine. You can let it idle without fail.

Just when you put it under load and start moving, it runs way too rich. This in turn fouls the spark plug, and gives you something between 15 and 50 miles of runway until the spark is so sooty that it fails igniting and the bike starts jumping, eventually bogging down.

Replacing with a new spark plug always fixes the problem and the bike is rideable like before.
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temeluchus
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PostPosted: 17:04 - 25 Jun 2017    Post subject: Reply with quote

it'll be a sensor most likely, MAF, airbox temp, coolant temp or the o2 sensor in the pipe. Does it have an ODB port? you might be able to see if one of them is telling obvious porky pies that way.
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Paulf
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PostPosted: 20:53 - 25 Jun 2017    Post subject: Reply with quote

If a sensor has gone does not the engine management flash like Honda's system. Sorry do not know yamaha ecm. I ask because it would narrow down if a sensor is faulty or connection bad. If you have a flash code type that in Google . I have an the codes are there admittedly for a yamaha 125. The ecm supplies the correct fuel for the required bang and its close loop system so somethings not right with the engine management system. A failed 02 sensor lets the bike run and if it's over fuelling the sensor will suffer like the spark plug and not work. You could have multiple problem O2 sensor for a start but that just might need cleaning. Before changing sensors though check the connections at the multi plug at ecm and check the various pins for continuity and power. For this I recommend a workshop manual or at least a wiring diagram covering ecm pins. I have the workshop manual for a Honda which gives expected volts etc for the pins. I have recently diagnosed a failed O2 sensor broken wire coming out the sensor so replaced. And the ecm reset and engine management light went out, all good. Note if you have a engine management light but it's not on I understand from on here a engine management light on is a mot failure and so the bulb is sometimes taken out to pass. You have not mentioned the light on and it should be due to the ecm sole purpose is to control emissions. Anyhow good luck.
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raystone
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PostPosted: 23:20 - 25 Jun 2017    Post subject: Reply with quote

Thank you, both — very good points.

The engine light has not come on. I've managed to get it to light up once, that was when the spark plug was completely and entirely done for, and also when the bike was in the heat of the sun with the former fuel pump.

But no engine light otherwise. So I suspect that none of the sensors are clearly broken (dead), rather, they may have drifted off with the reading if anything. There's no code on the dash, as this YBR 250 does not show them there. It needs a diagnostics device (Yamaha FI Diagnostics Tool), which I have now reluctantly ordered from the Netherlands. Should arrive this week, and it'll allow to fine-tune lots of things but most importantly, it'll read TPS sensor and other sensor things (including air/fuel mix I hope). So that will hopefully help in getting a better idea.

Also, I have a compression test kit arrive tomorrow, which I'll also give a quick try, just in case (and to rule engine compression issues out). I know a leak-down test would've helped to understand more of what the actual failing component would be, but I'll start with the compression test.

We tried an Iridium spark, but it went out today (we put it in yesterday, and rode around all day today, stop-and-go for 20 miles or so). Those sparks are getting expensive.

Anyways, I'll also try to measure the O2 sensor tomorrow, if I can somehow, after warming up the bike, to see if it measures/reads anything useful.

Finally, I've found a guy who sold me the English YBR 250 manual, so I'll see if there's anything else in there.
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raystone
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PostPosted: 18:12 - 26 Jun 2017    Post subject: Reply with quote

Compression test completed. Service manual says standard is 170psi, minimum is 152 psi, and maximum is 188 psi.

I've had readings at around 160 - 162 psi, so that's within range. And the engine wasn't properly warmed up yet (just a bit).

Note for others trying this (in the future): make sure you do keep that trottle wide open (as it says everywhere) to avoid unnecessary panic.


Then I've tried to measure the O2 sensor, and wanted to get a closer look at it (potentially measure it at home) — but I destroyed two out of three screws in the process and now can't get it out (see image, ideas?).

I did manage to measure the O2 sensor against battery ground, but had the bike not properly warmed up, when started, it started reading from 0.75V to 0.85V within a few seconds, and then stayed mostly at 0.85V (which is super rich, and it smelled exactly like it).

I also entirely disconnected the O2 sensor and started the bike (which didn't put on the engine light, surprisingly — it just lights up for the initiation sequence, then disappears normally). It made the bike run lean, I think (very light gray/white smoke). Didn't wanted to run it too long like that, so I connected it back, none the wiser.

I have a diagnostics device arrive in two days, and hopefully, this will allow me to get an idea of the sensors. But if the engine light isn't coming on, I have my doubts the diagnostics device is going to reveal a solution.

Service manual says (in case of rich mix):
1. Check O2 sensor for looseness or pinching. Done, noticed nothing (and sprayed it with electrical contact cleaner, just in case).

2. Check for open/short circuit in wire harness (I've got an electronics degree, but that seemed overly complicated to check across the entire bike? Or did they mean just the connector?)

3. Check fuel pressure (haven't done that, but I installed a brand-new fuel pump, which didn't seem to do anything other than fixing the too hot in the sun problem). I wonder how I can check fuel pressure without ordering yet another piece of kit.

4. Defective O2 sensor (unable to output a lean signal) — could be. Not sure, as the sensor itself on the bike won't read lean as the underlying problem is that it is running rich. So I'd need to take it out (which is what I failed at due to the damaged screws) to test it properly.

This is one piece of a puzzle.
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Paulf
Nova Slayer



Joined: 24 Jan 2017
Karma :

PostPosted: 19:41 - 26 Jun 2017    Post subject: Reply with quote

Honda state remove ecm plug switch on at the ignition then tells you the pin numbers to check for continuity and voltage. With the wiring diagram you could work out which pin which sensor so to speak.
____________________
Past bikes simsom mofa 1s, suzuki hustler 250 (£35 in 1973), suzuki ts125k, mz150, yamaha yb 100, honda pc50, honda vision 50, all 2 stroke - then cars - honda pcx 125 (sold) own honda fes 125 and Mrs 125 spares or repairs. Started 1972 all accidents walked away no insurAnce claims
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Paulf
Nova Slayer



Joined: 24 Jan 2017
Karma :

PostPosted: 20:01 - 26 Jun 2017    Post subject: Reply with quote

Sorry read more when my 02 sensor had one out of four broke the engine management light came on and would not go out. As stated previous the ecm makes the bike compliant with the emission regs, that's all. Therefore when the o2 connector was disconnected the light should stay on. Puzzled to say the least because the o2 sensor is top of my list that has failed it has the biggest influence on post combustion richness in a close loop system. Perhaps it is signalling over richness but the system cannot adjust therefore where is the light. I am not sure but it seems your ecm is being overridden or told electronically to say nothing.

As you state the you have measured the o2 voltage mine is 0.1 to 0.3 v standard at idle for info yours therefore seems high by comparison.
____________________
Past bikes simsom mofa 1s, suzuki hustler 250 (£35 in 1973), suzuki ts125k, mz150, yamaha yb 100, honda pc50, honda vision 50, all 2 stroke - then cars - honda pcx 125 (sold) own honda fes 125 and Mrs 125 spares or repairs. Started 1972 all accidents walked away no insurAnce claims
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raystone
Two Stroke Sniffer



Joined: 21 Feb 2016
Karma :

PostPosted: 13:43 - 18 Jul 2017    Post subject: Reply with quote

Just wanted to post this here as a solution as well — I've finally resolved the issue after weeks and weeks of trying everything, studying everything, buying everything. Since you guys have been nice enough to suggest some starters, I suspect you may be able to tell someone else some other time about how this can be solved.

I've attached a photo of the culprit:

https://i.imgur.com/edF0d8h.png

It was the Yamaha hybrid sensor (attached to the throttle body). It has faulty o-rings, and they let fuel and other things leak in. All that stuff starts accumulating to nasty crystallized dust and sand. This eventually seems to let air in when the vacuum starts building in the throttle body, and that in turn messes up the ECUs sensor readings (air inflow/temp, etc.)

The solution is to clean this up (it fixed the issue immediately). And then to order the replacement OEM parts from a Yamaha dealer (30-40 quid for two o-rings). Yamaha has replaced the original parts with better material, but of course, no word anywhere for those looking at possible solutions.

The effect is quite severe, for what seems to be just a little skew in readings. The engine idles perfectly normal and calm. So measuring the sensors all seemed to be perfect, I used Yamaha's diagnostics device, multi-meters, and all that. While compression of the engine has gone down, it's far from being the culprit. But once you start riding and putting it under pressure, the sensors run off and the ECU starts messing up things dramatically.

All that stays within the sensor limits, so the ECU does not detect any abnormalities other than running rich.

Before finding the solution, I checked and replaced: oil, oil filter, air filter, sparks (replacements, and Iridium), did the valve clearances (kinda proud I got those done right), compression tests, measured/tested/cleaned ignition coil, cleaned entire throttle body, tested fuel injectors (cleaned/tested the valve using a battery), ran fuel injection tests, tested TPS, checked all tubes for leaks and ran leak tests, tested the O2 sensor, cleaned fuel tank, replaced fuel pump and fuel pump filter, and probably a bunch of other things that didn't make a change.

What a mess that was, and how simple a solution. Before, it ran maybe a few miles until the spark-plug gave up (sooty) and the bike was stranded dead. After cleaning the sensor and replacing new o-rings, I've done 700 miles on it now without a hitch. I am happier than happy, but holy hell that was one journey. I've learned so much on the way, it's incredible.

Anyways, thanks for helping me out.
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There is a gap of 3 years, 19 days between these two posts...

FeniX-
L Plate Warrior



Joined: 06 Aug 2020
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PostPosted: 10:59 - 06 Aug 2020    Post subject: Reply with quote

raystone wrote:
Just wanted to post this here as a solution.


Hi, do you still have the bike?
Nice debugging though.

I just wanted to ask, can you write down the steps for setting the valve clearance. (especially the steps for removing the fueltank)

I've done it previously on a yamaha srx 400, but there i spared to remove the gas-tank.

Now, i had a similar ybr 250, and as i saw, i wan't get past that step.
Can you help me out with that?

thanks!
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kr,
Béla
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Old Thread Alert!

The last post was made 3 years, 235 days ago. Instead of replying here, would creating a new thread be more useful?
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