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Tough Start Question

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I have a 05 kx250f. runs great, pc ti-4 exhaust is all that is modified. maybe 150 hrs. intermediate rider. this is my first 4 stroke. All of a sudden out of no where, the thing will not kick start, and seems to have little compression. you can bump start it fine, and it runs great, just like usual. any one else have this problem, or have possible solution?

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To many possabilities and not enough information to speculate on the cause.

Things you can do are:

Check the plug for any indication rich/lean

-rich might indicate excess carbon build up on valves and therefore inconplete closure.

Do a valve adjustment check to ensure they are within specs

While checking the valve adjustment heck/adjust (if possible on the 05 KXF) the decompression engagement specs.

-this is possible on the Hondas and can be adjusted

Have the compression checked to see if it is out of specs.

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I have done all you have suggested, except compression check, and i just got the right fitting today, so that is gonna be tonights test. what about the auto decompresion lever on the cam? do you know anything about that? the plug looked good, the spark was good. and even if there was carbon build up on valve seet wouldnt I loose power? thanks for the advice!

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last time thath happened to me my valve was burnt up

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If the valves are within spec and it turns out the compression is good, and you are only having issues trying to start it (i.e. not down on power) then I would think you should look at the decompression device. As I indicated this is something that can be adjusted on the Hondas, and it is effected by the valve adjustment. I am not sure yet about the KXFs being adjustable.

If compression is down then you will need to look at valves and/or rings (top end). If you have not down a top end on this bike yet, you should, and have the valves lapped as well. Performance will increase.

Good luck.

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If I do not disable the decomp I get a comp reading of about 95 lbs. I have gotten that reading on more than one bike.

Merlinn

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I am not sure that this reading will have much meaning (unless really really low) as it can change with the adjustment of the decomp.

In order to determine if you need to get into the top end (valves or piston/rings) you need to know what the real copression is (sans decomp), then check with the local dealer to see if you are good.

If your within specs on the compression, the good news is that would indicate the decomp needs adjusting. The alternative would be if you are down on compression....your doing the valves/top end.

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One more quick thought... check your pilot jet, and the passage ways. A good carb cleaning could be in order. Also confirm your fuel screw setting, I have a Scotts T handle fuel screw and it makes it sooo easy to check and adjust. Your on the right track with valve check, plug and clean jets.

Good Luck,

Merlin

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Thanks for all the help guys.. boy I use to think I would never miss a 2-stroke.. I guess this is the only thing I miss about one, they are alot easier to diagnose. The compression actually checked at about 65 psi cold, and 150 hot. I re-checked the valve clearance, and the left intake was tight. so I am gonna re-shim both intake valves to about .005 clearance.

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Just check your valve clearance. I have had this same thing happen numerous times on these bikes. I would bet one or both of your intake valves have closed up their gap.

Jimbo

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Just check your valve clearance. I have had this same thing happen numerous times on these bikes. I would bet one or both of your intake valves have closed up their gap.

Jimbo

yep..same happened to me..had many hours on my bike and than randomly my bike wouldnt start ever it took so long to kick over and got to the point that riding sucked and i wanted to go home...i checked them and both intake clearances were super tight....

go buy a hot cams shim kit for around 70 bucks

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I had a simular issue and it was the throttle linkage had some dirt and would'nt close but was idleing a little high once I started to. Just a thought

:banghead:

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hey i bought my bike with that same problem, let me know if you have any ideas on what the problem might be

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hey i bought my bike with that same problem, let me know if you have any ideas on what the problem might be

check the valves....whenever there is a hard start problem always check the valves.

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The service manual for an '06 says the cylinder compression should be between 63-102 psi. That is with the auto-decompression still attached. That range sounds a bit wide to me.

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With 150 hours on the original motor I can guarantee it's the valves, no big deal just rebuild the head to like new specs and go again. If it were a two stroke with 150 hours, it would need a top end don't you think?

I will never understand how anyone can expect these high revving race motors to last forever. In the manual it says to check the valve clearance about every 6 races thats about every 6 hours plus or minus. If they need adjustment it means they are wearing out. If they are wearing out, replace them. It's just part of the deal with these awesome new bikes. Lets face it, your old two stroke can't even come close to the performance of the thumper.

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i had some problem !!! bought my bike drove for like 1hr in the shop!!! $1,350 bucks in parts and stuff now!!! Buying cyclinder head intake cam kibblewhite valves and springs and all gaskets!!! i will post pics and show you what happends if you don't check them and just drive lol!! if anyone wants to see them!!!

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I brought my 2004 in. The only engine work was an oil change. I get it back and the kick is like a 2-stroke now. too easy and soft. it starts, but requires a little different technique. can the valves get out of wack from one trail ride? it started great my last ride. even now it runs great.

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