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250f not starting after top end rebuild


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I had another thread detailing some of the issues I encountered during the rebuild, but figured another thread with the specific issues I'm having now is in order.

The background: 07 250f, 73 hours. Did a full top end end rebuild. Intakes were all just a little too tight, so went one size smaller shim in each valve. Valves perfectly in spec now. Bike ran like a top before the rebuild, but figured a new top end was long overdue.

After getting it all buttoned up last night, it fired and idled, but died with any throttle application. I also noticed that fuel was literally pouring out of the bowl drain, which I thought was very strange since the bike ran great before I tore it down. I took the float out and cleaned the needle seat and everything in that area and put it back together. It didn't look dirty, the float height is exactly to spec, and nothing looked out of place or worn. I reassembled, and now there is no more leaking fuel, but the thing just refuses to start. Fuel is fresh.

It was a 1-2 kick bike prior to the new top end.

I am on the verge of getting extremely frustrated with this thing.. I just don't know where to turn. ­čśĆ

Any ideas, before I start taking it apart for like the 9th time in 12 hours?

Is there a specific starting procedure I should be using after draining teh float bowl?

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Wow, ninth time in twelve hours - OUCH!

I don't know if this will help, but when I did my top end rebuild on my '07,

I had it all buttoned up like you said, and mine fired after a couple of kicks and then died on throttle application.

Took it back apart, and found that I had the rings on the piston at the wrong degree locations. Mine were almost all in line.

If you look closely at the piston, there are tiny holes at the degree location markers as stated per manual specs in the piston ring slots. The opening on each of the top rings should allow you to see that tiny hole.

Hope this helps!

Later and hopefully Ride On!

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I never knew there where holes in the piston that indicate where the ring gaps should be, but I did set the gaps in the spots the manual calls for.

Even if they somehow ended up being completely lined up, this would only create a low compression, or possibly poor oil control situation, right? That wouldn't cause it not to start.... right?

What's most frustrating is that this bike ran absolutely perfectly and started on the 1st or 2nd kick every time before I did the top end. I have to leave for a race on saturday morning... starting to wonder if that's gonna happen. ­čśĆ

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I never knew there where holes in the piston that indicate where the ring gaps should be, but I did set the gaps in the spots the manual calls for.

Even if they somehow ended up being completely lined up, this would only create a low compression, or possibly poor oil control situation, right? That wouldn't cause it not to start.... right?

What's most frustrating is that this bike ran absolutely perfectly and started on the 1st or 2nd kick every time before I did the top end. I have to leave for a race on saturday morning... starting to wonder if that's gonna happen. ­čśĆ

Right, it would result in low compression and oil control, and if you have low compression because of this, you are not getting the proper amount of intake air after the cycle completes.

But like you said, you have them correct, I was just thinking anything outside of the carburetor that might help.

Did you make sure that there isn't a kill switch failure?

I mean I don't want to ask you things that are obvious, I want to go after things that when you do a rebuild, it's like well, I didn't even touch that part of the bike - how in the heck did that happen?

My second rebuild of the top end resulted in me acquiring a kill switch failure and I have no idea how - guess it was just its time to go out.

I was getting continuous when the kill switch wasn't pushed in and had to replace it.

If you get no continuous while its pushed in, you also have to replace it.

It all comes down to its resistance, and a switch can fail open or fail closed.

Later.

Edited by nokickstandsallowed
Added thought.
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it's like well, I didn't even touch that part of the bike - how in the heck did that happen?

Exactly man.... that's what's been so frustrating. I guess I should start from scratch and check for spark. ARRRRRG.

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I hope you nail it!

As far as I'm concerned, the electrical aspect of the bike only takes about 10 to 15 minutes to go through the steps and should be in the first section of the manual, not the end part of the manual.

I can't even begin to tell you how ticked off I used to get because I would tear down the bike, and it was something electrical (outside of checking for spark on the plug) like the TPS or kill switch, etc. etc. etc.

I hear ya also, and nail it down my fellow rider!

Edited by nokickstandsallowed
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  • 2 weeks later...

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