Yam YBR250 running rich - FI Diagnostic Tool CO adjustment

[andy1303]

Hi,

I'm new here so hope you can help with a problem I have.

A while ago I purchased very cheaply a rather rough YBR250. It was showing Fault Code 14, faulty intake air pressure sensor.

Now, this bike has a combination sensor which measures TPS, intake air temp and intake air pressure. Web searching brought up the suggestion to clean it, but after no luck with that, I replaced it with a Chinese copy. This resolved the fault code and the bike seemed to run fine.

I went for a couple of long runs, and it seemed fine, but after using it on some very short runs I found it was fouling the plug. Once run it just died and I had to get recovered, another time it started and then just died, refusing to start again until I replaced plug.

After more web searching and reading the factory service manual I came across the CO setting, which is accessed using the Yamaha FI diagnostic tool. This setting appears to adjust the richness at idle. There is a lot of information here https://www.thumpertalk.com/forums/topic/1145194-yamaha-fi-diagnostic-tool-wr450-specific/#comments where they seem to adjust it to get better starting.

I decided it was worth buying the Yamaha FI Diagnostic Tool. Today, I took the bike for a run to get the bike warm, and then tried adjusting the CO. By lowering the setting from 0 to -40, the tickover started to pick up, as if the mixture was getting leaner and closer to the ideal mixture. Lowering it to -60 raised the tickover even more, however I decided to leave it set to -40 where it would be at the richer end of the scale. I didn't have the bottle to keep going to see if I could lean it out to the point of tickover dropping again.

While I appreciate the numbers do not directly correlate with a specific AFR, -40 and -60 seem quite extreme. I was wondering if anyone has any experience with the FI Diagnostic Tool and adjusting this CO setting? Does my logic appear right?

It's a bit soggy outside at the moment so I haven't had a chance to go out and see how it cold starts.

Any thoughts or comments would be much appreciated.

Andy

[WD Forte]

Is this a pukka Yamaha diag tool?
does it give you live readings from the various sensors?
if so, I'd want to see what the temp sensor is doing before
making changes just in case it's performing badly.

If its under or over reporting but not failing enough to throw up a fault code, this can put the mixture out.
Bad contacts or grounding can have similar effects too, not sure but I think some of them only have 5v signal level so not much wiggle room.

Then there's the fact its a Chinese copy.
Might be a good copy with matched sensors, might not.
I only have experience with the 125 and the Haynes manual doesn't offer any in depth info on the EFI/ECU
A list of fault codes is about as far as it goes
____________________
bikers smell of wee

[stinkwheel]

You have to wonder why it's running so rich on stock FI settings.

Is there a rats nest in the airbox? Might be worth a check because I don't believe there's a sensor to check that.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[andy1303]

Yes it is the genuine Yamaha tool. It does give live sensor readings.
Do you mean inlet temp or engine temp?

The connection to the multi-sensor was good if I remember rightly.

Yes I agree, the Chinese sensor was a bit of a worry, but neither Mikuni or Yamaha seem to list a genuine replacement. YBR250s are pretty rare so getting a used one is difficult and may just bring up the same problems.

I would really recommend getting hold of a genuine service manual, even a pdf, since they really are very good. There isn't a Haynes manual for the 250.

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I replaced the air filter recently so I'm pretty sure it's clean in there.

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Thanks for both your thoughts, it's much appreciated.

[WD Forte]

I dont have a YBR125 and probably never will, I've just done a lot work on one for a
guy who doesn't know where the spark plug is and he's left the Hyenas manual with me.

take a good pic of the 250 wiring diagram and show us, any other related pics too
we likes pics we do
it would be interesting to compare it to the 125

The engine temp sensor would be of particular interest to me initially
to see how it behaves as the engine warms up
Most temp sensors are are NTC (negative temperature coefficient)
so the resistance drops as they get hotter
They form part of a voltage divider where the resultant voltage is read by the ECU
as a factor in the fuelling calculation.
for comparison, The 125 temp sensor should be around 2500 ohms at 20C and 200 ohms at 100C

In fact, the pressure sensor probably behaves in a similar way as well so I'd be taking a very close look at the old throttle body assembly to see if I could get in there to tinker with it.
Just had shufty at the manual and the 125's IAP sensor read between 3.75V to 4.25
so as I said, not a lot of wiggle room

What model of Mikuni is it?
____________________
bikers smell of wee

[andy1303]

See attached images of wiring diagram and key.

I connected the FI Diagnostic tool and checked TPS, IAT, IAP and engine temp before and after a run out.
Obviously TPS didn't change although it was slight out of spec on closed throttle.
IAP could be seen to vary when I turned over the engine but there isn't a spec in the manual.
IAT and Engine Temp were roughly as expected before and after the ride.
IAT 9 degrees before, 25 degrees after.
Eng temp 12 degrees before, 69 degrees after.

I don't know the model of throttle body. What I do know is that similar throttle bodies with the same/similar sensor are used on approx 2008-2013 YBR125s and YZF-R125s.

[Nobby the Bastard]

FI should do all that shit by itself.

Has it been remapped?
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[Kawasaki Jimbo]

I wouldn’t be mucking about with Yamaha’s “CO” setting whatever it is.

It’s likely that the “Chinese copy” sensor is OE, possibly minus the Japanese quality control but not necessarily ‘different.’

Is this thread of any use - https://www.bikechatforums.com/viewtopic.php?t=320502#google_vignette

[WD Forte]

Well done you finding that
I can't even find my own old posts on here

definitely a possible culprit

https://www.bikechatforums.com/download.php?id=99945
____________________
bikers smell of wee

[andy1303]

I can see no reason why this bike would be re-mapped. It's a scruffy inexpensive commuter bike.

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Yes I read the thread about the hybrid sensor before I bought the bike. It was a contributing factor to me thinking it was worth taking a punt on it. That sensor was the multi-sensor I replaced. It came with a new rubber gasket, which I used when I installed it, and I also put a new o-ring around the long fella at the top of the picture.

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So today I went out and checked the spark plug again and it is still very sooty. I then returned the CO setting to 0, as per before I adjusted with it.
I then got the bike running and had a good liberal spray of brake cleaner around the throttle body, hybrid sensor and the joints on the air induction system. No change in idle rpm.
I even tried blocking the air induction system to see if that made a difference, and it didn't.