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HELP Won't Start

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I have an 04 kx250f, last weekend me and some buddies went out and rode pretty hard all weekend, at the end of the last day my bike was backfiring like there was no tomorrow. I got home changed the oil, filter, air filter, put a new plug, now it won't start i kick for ever it fires up here and there but sounds rough and will not idle, even with the choke on if i let go of the gas it stalls....what to do first...(i changed the plug from cr9eb to cr8eb)...valves, plug, piston.. can you please help

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check the valve clearances. if they are out then it will be really easy to kick, but it wont start (no compression=no start). while you are checking your valves look at the buckets, the stock ones break and where really easy, just look for round spirals on the top of them, the should not have any spirals. good luck.

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1. Check valves,

2. Check valves,

3. Check valves.

It will probably be the left intake valve has recessed and you no longer have any clearance.

One of the first symptoms of valve recession is hard starting not "hard to kick over". It's probably is now easier to kick over, won't idle and will cut out in corners for no reason.

If the clearance has closed up, you can re shim it but that is only a temp measure. That valve is rooted and will keep closing up. The fix is a new valve and some head work.

I went with softer seats and Ti valves and they have not moved since. I do a heap of riding as well. Over there stainless valves/new springs etc seems to be the go.

Start searching through posts for the answers, there's a heap of info out there.

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I had the exact same problem. It ended up being that my 2 intake valves had almost shattered! Anyways after I put new valves,springs, etc, my bike ran great for the first few rides, and now I sometimes go to start it when its hot, and I hardly have any compression for 20 or so kicks, then it will finally gain compression and start up. It has alot of compression when its cold and starts fine when its cold. Would this mean that the valves could of got out of whack, and the clearance could be off?

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A valve could be hanging up in the guide or they are so close to being out of adjustment that when it heats up it looses clearance.

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While you are checking the valves, look at your cam lobes in comparison to the hole in the cam sprocket. The tips of the lobes should be in line with that hole. Our bike spun the sprocket on the camshaft (the tips were no longer in line with the hole) effectively changing the timing of the intake valves and the bike wouldn't start. Valves, however, were still in spec. :banghead:

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Ok thanks for the help guys, I will be checking the valves fairly soon. Stezlaki you could be right about the camshaft and the timing being off because I was talking to a mechanic and he suggested that I look at the timing because he thinks that it is off by a little, he also said that the backfiring when I try to start it is a sign of the timing being off, is this true or no?

Thanks

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............ backfiring when I try to start it is a sign of the timing being off, is this true or no?

If I remember correctly, your description of what your bike did/is doing is pretty much what ours did. I think the last time it actually started, it ran like sh:censored:, then wouldn't even start at all, but would backfire every now and then.

If I were you, I'd pull the valve cover and check things out before even trying to start it any more. If, by chance, you do have a similar problem and the gear were to spin even more on the camshaft, your valves could get enough out of time to hit the piston and really screw things up. It only takes about 5-10 minutes to get in there and see what you've got.

On edit.......

I was confused:bonk:.........thought you were the original poster (Kawy), so I guess our bike didn't exactly do what yours is doing. I'd still pull the cover and take a look.

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Ok I will check them sometime this week before I start it/ride it anymore. I am new to all this valve stuff and everything (I came off a 2-stroke), so could you tell me what exactly I am looking for. Your help would be appreciated.

Thanks

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