Advice needed on wr250r low compression + hard to start

Jens Eskildsen wrote:

What does the engine do, based on coolant temp, other than start the fan?

It also changes the air/fuel ratio, so when it detects a very low temperature it would enrich the mixture -- which would explain the hesitation of the engine as it finds itself with too much fuel for the given high ambient temperatures.

Yes and combined with the low compression bad times.
I'll change out the ECU and see if that fixes things.

I won't be able to do more in-depth testing of the system until things are back together, so thats on the to doos.

Heres a shot of valve town:


Looks fine to me.

Thanks guys, hopefully I'll get somewhere when new bits arrive.

Much better!

In the first picture the right input valve shows two rather prominent pits; however, they are not visible in the last picture you posted.

Was that just the lighting?

Yeah just the lighting - they are in good condition thank god.

Hey guys.

So waiting for parts, so I've had some time to look into the crank case.

The con rod has some slight vertical play

I guess that needs to be ripped out....

Edmonton wrote:

The con rod has some slight vertical play

Although this is terrible news (makes you wonder what the previous owner did to the bike), I don't see why this would affect cold starts: if the excessive play results in the crank position sensor being off, that would happen at all temperatures, not just cold.

I still think that the root cause is somewhere in the ECU, misreading the coolant temperature sensor seems to point to it.

Agreed.

Waiting for the parts, engine is out - half way through prepping for split.

I'm trying to brainstorm, on the rebuild how I would fold up the locking tabs on the clutch nut washer?
Here is the a picture of the area as I took it apart.

As you can see you cant access the side of the lock washer in order to peen it upwards....

Worth posting as a new topic perhaps....

OK!

So new ECU installed.

Still doesn't read voltage or coolant sensor. Engine warning light still on.

At a loss here.

Water pump pliars will bend that washer no problem. If you need to make more room for the wrech to grab, use a screwdriver and hammer at and angle, to lift the washer up a bit. Im a bit concerned that youre tearing apart an engine, and stuff like this sets you back.

Its ment in the most respectfull way. We're here for you, have a nice day.

Sounds like a good technique, its great to have access to such a community - honestly these tips are so valuable.

First engine repair, lets see what happens!

Ed

Looks like a few channels were blocked by the liquid gasket.
This cannot have been good for lubrication system.

Actually, the new Yamaha gasket will have a bit of gray-colored sealant already applied to the gasket in that area.
Just carefully remove that old sealant and clean the surfaces the gasket will contact.

YZEtc wrote:

Actually, the new Yamaha gasket will have a bit of gray-colored sealant already applied to the gasket in that area.
Just carefully remove that old sealant and clean the surfaces the gasket will contact.

I think you are mistaken, this is a liquid applied gasket, not a plate gasket.

Edmonton wrote:

OK!

So new ECU installed.

Still doesn't read voltage or coolant sensor. Engine warning light still on.

At a loss here.

Wow!

I'm at a loss here too. This is one of these cases where you have no other option but to take the bike to the dealer, but I'm afraid there won't be a lot of dealers with the expertise to diagnose this problem.

Is there a dealer in your area that you can trust?

I'll ring around a few places, see what I can find.

Any road up, ill need to put it back together again.

Incidentally the oil pump was not moving smoothly, and with some internal marking.

Edmonton wrote:

Incidentally the oil pump was not moving smoothly, and with some internal marking.

Looks consistent with the blocked lubrication channel you discovered earlier. Might also explain the scoring of the cylinder sleeve.

This bike seems to have been abused maintenance-wise.

Do you know why the bike has been opened up before? You might get a clue there...

I suspect some dealer changed the cam chain as a "well this might be the problem" solver.

I don't think anyone has split the engine before however.

I agree that the lubrication system has been compromised, the main bearings feel a little rough too.

Lets see what the feel of the thing is when its all back together....

Thanks guys.

Ed

Major development guys!

Just finished up the rebuild. All went as expected - I have to say the workshop manual is entirely brilliant.

Started right up!

Here is the kicker.....

The last resort for the coolant sensor error, was to replace the sensor. (remember the previous owner had done this...apparently). Oh and remember that it was all in spec as per the workshop manual.
Oh and remember I did the whole put it in coolant and heat it up and check specs test - passed.

Replaced it.

NO MORE WARNING LIGHT. FFS!

A MASSIVE thank-you guys for all the notes as this went along.

So pleased with the outcome, enjoyed the rebuild, learned much.

Get back to the fun stuff now!!