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2000 XR250R - rebuilt top end - doesn't start (still)

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Short version of the story:

  • Rebuilt engine - new valves, springs, piston, valve stem seals, head and cylinder base gasket.
  • Bike started first time nice and easily.
  • Bike backfired and stalled when blipping the throttle.
  • Bike won't start again.
  • Have tried kick starting, and tried using Aerostart sprayed into the air intake.
  • Have tried roll starting down my hill - back wheel locks up and skids.

The long detailed version:

A few months ago, my 2000 Honda XR250R wouldn't start. After assistance from here, we determined the cause to be the recessed inlet valves (see http://www.dirtbikeworld.net/forum/showthread.php?t=81945&page=7 and https://thumpertalk.com/forum/showthread.php?t=989916&highlight= for more information). After some stuffing around getting parts locally, then turning to the USA and some wait time, it is finally back together, but now with a XRsOnly 78mm JE Piston, Ferrea stainless steel inlet and exhaust valves, new genuine Honda valve stem seals, Cometic head and cylinder base gasket and Kibble White Titanium Valve Springs.

Put it all back together, kicked it over and bang off she went. It started so so so easy (like a dream). I let it idle for a bit, waiting for it to warm up so I could check the engine oil level. I bliped the throttle a few times, and on one of them the bike backfired stalled.

I had been stuffing around with the Edelbrock pumper carby. I got this idea that because of the extra 35cc's I should go up a needle, so I put in the 17E needle (which I have since been told is too large and have gone back to the original standard 15E). So I assumed that it was running far too rich and this was caused the stall.

Bike wouldn't start again. Tried kicking numerous times, no good. At this point I noticed that the bike has a lot of compression. It is bloody hard to kick through at some points.

The next day I tried roll starting it down my hill in both 1st and 2nd gear. As soon as I let out the clutch, the rear wheel would lock up. I then redid the valve clearances. Tried again, no good.

I then removed the spark plug, and checked that it was sparking - it was. Upon reinstalling the spark plug, I managed to strip the thread. So off came the head again.

Head went into the machine shop and had a helicoil fitted. While the head was off, I check the piston movement. I also checked the valves seal - I poured petrol into the intake and the exhaust, but they seem to be sealed tight as none seeped through. I also checked over the carby and it seems to be in excellent fully functioning condition. Last night I reassembled the bike, due to being late I wasn't able to try and start it.

Today I tried to kick start it. Still no start. It back fired a couple of times, but that was after I sprayed Aerostart into the air intake to try to help it to start.

It's raining and fairly foggy, so I can't try roll starting it down the hill at the moment.

Any ideas?

Does it locking up when trying to hill start signal anything such as too much compression?

Edited by twr7cx

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i very much doubt you got the same problem i had,but this is what happened to me,coincidently just after i got it back together after installing a 78mm piston,

kicked bike over,had it running for about 20 secs,all seemed fine,then cuts out and couldn't get it started again,

next day wouldn't start ,checked all the usual stuff,decided to re do valve clearances,lined it up on T mark and clearances are way off,reset them and tried kicking it over,was really hard to push the kickstart down ,but tried kicking it until i couldnt kick no more anyway 👍 no way it was going to start,

took the head off and turned engine over,could now see that the piston came up over tdc and was half way down again before the T mark lined up,the woodruff key had sheared,the flywheel had spun around on the crank,and wedged itself way out of position,so when i redid my valve clearances it was miles from tdc,which had caused the valves to come into contact with the piston,which was why it was so hard to kick it,had to replace a couple of the valves,

like i said chances are its something else,although your experience sounded kinda like mine,but worth checking,

also mine got real hard to kick just before the big end let go,ive had some bad luck with this bike

Edited by nick cresswell

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Yep..You never know..Carb hasn't blown off the manifold has it??

Cam chain may have jumped or as nick says woodruff sheared off thus stuffing up all the timing..Really the head cover needs to come off for you to check the timing again. Those sort of backfires are generally something to do with timing or too tighter tappet/valve gaps..

You're jumping it in 1st,,2nd,,..Try a larger gear (higher)..sounds like it has 600 type compression and you sure as heck don't try jumping one of them in anything lower than third..Kinda wonder why people want all this hot high compression gear..standard you know it goes..hot this and that you never really know whether she'll work correctly.

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Like the previous posts said , take it apart and check everything again. You have to much money invested so don't make thinks much worse by repeated kicking.

If it won't start theres a good reason. I have never been a fan of using starting fluid , just a bad idea.

First check that T mark is at TDC , valve clearance, spark, fuel system. Wire connections ? Kill button

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i would suspect it to be one of the following.

1: fuel related like bad intake gasket or gunked carb

2: wrong timing

3: not getting a spark

4: none of the above

you will get it going enjoy! 👍

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It's been a busy last week. Finally today I got to have another look at it and try to roll start it. I went down the hill in 4th gear. On a positive note, when I popped the clutch out the back wheel did not lock up and skid, instead it turned and it turned the driveline and engine. I could hear the engine noise, the sort of dodododododododododododo, I assume from the piston going up and down and compressing the air and then releasing it through the exhaust system.

But it was not firing. While rolling down with the engine turning I hit the kill switch, and that did not change the noise at all!

So tomorrow I'll have to pull the top cover off again and start tripple/quadrouple checking things... However, based on the fact that it has run, I'm thinking something electric is going to be the problem...

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I would bet on a slipping woodruff key.

Is that the woodruff key on the flywheel on the left side where the electric stator is?

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Is that the woodruff key on the flywheel on the left side where the electric stator is?

yes it holds the flywheel in position on the crank,until it breaks

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yes it holds the flywheel in position on the crank,until it breaks

Cheers. I'll crack the left side open and have a look.

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Ha ha, she runs, finally! Only 8 months or so now (admittedly time has been short)...

Took it to a bike mechanic who did it as a back yard cashie. He looked over it on the first day and found nothing obvious. He then removed the cam and carby, pulled the carby apart, refitted the cam, adjusted the valves, etc., tested the ignition system. When he put it back together it ran. He suspects it was the carby, that it was a bit gunked up (said not to run Premium Fuel any more). $150.00, bargain!

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