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Long story short I bought a project bike that looks like someone's old race bike (first mistake). Bike is an 05 Crf250x. It had been sitting for 3 years and was being sold as is. Guy swore that it was his son's bike and it ran great before he parked it. I knew it was a gamble but such a good deal I couldn't pass it up. 

I Checked the valves and they were with in spec, replaced the spark plug and totally rebuilt the carb with new seals and a new pilot jet, and changed the oils and filter. Oh and cleaned the gas tank really well. 

Jump forward to now I filled it with fresh fuel and started it up. Bike ran amazing for about 30 seconds. Super crisp! Someone that built this bike really did a good job tuning the carb before me. Carb has Boyesen Quickshot ect. So I gave it a couple quick twist of the throttle and then it was idling and something came loose. Sounded like a cam chain started chattering and bike stumbled and died. kicked it a little and no go. still felt like it had compression though. Removed valve cover and timing chain is tight and nothing looks abnormal with valve springs.

Any ideas on what might have happened or some non intrusive tests I can do with out pulling the head off? Any tips or engine failures that you've seen would be much appreciated.

Thanks!

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Might have idled low and the decompressor kicked in.   Idle needs to be up at 1,700 rpms.

I would:

1. Turn it over slowly by hand and see if there are any odd noises or if anything doesn't feel smooth. You will have to get over the compression stroke which can feel rough, but still if anything is majorly wrong, you should hear/feel it.

2. If anything sounds odd (or just for peace of mind), check the oil filter and/or drain the oil to check for any metal flakes.

If that pans out then:

3. Next, a *small* squirt of starting fluid or WD40 and see if it will bump. 

4. If it does, check the fuel flow at the carb.  Often on the older bikes, the mesh fuel screen in the tank collapses or breaks up, or the fuel line breaks up, all of which results in junk in the carb.   If no flow, open the gas cap a bit.   It may be a plugged vent (usually though, you'll get some flow and then it will taper off).

5. If fuel flow is good there, open the carb drain and check for good flow there.  If none, then you have a stuck float.

6. Make sure the air filter is not over oiled.

See where that gets you.

Jim.

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Removed valve cover and timing chain is tight and nothing looks abnormal with valve springs.

 and BTW, when you did that, did you check the valve timing?   If it's an older chain, it's possible it jumped a tooth or two.

Jim.

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Good points thanks!

I did slowly turn it over with out the plug installed and I don't believe I hear anything bad. Kinda hard to hear anything over the noise of that decompression clink. Normal I believe. 

I did not check the timing. I'll do that too.

Fuel flow is good. 

I'm going to drain the oil and see what that looks like.

Oh and btw it has a 280 big bore kit and an R-head if that matters.

Edited by Fordfan1

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