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YZ400FPower

YZ400f.......problems

15 posts in this topic

I have a 1999 yz400f. The bike still runs but it is acting funny :p . If i was to go out to the bike i could push the kicker down as many times as i wanted,sometimes it will start and sometimes it takes 30 kicks to get the beast fired up :p , but sometimes the kicker will be stiff and you have to use the correct starting procedure :ride: . I just got the valves done thinking that that would solve the problem....it didnt :p . I am now thinking it could be the rings :lol: ..............please tell me what you guys think. :applause:

ALSO......if i went to a 03yz450 would it be a huge diff?..Just now getting into jumping and racing. :lol::p

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The newer the better. It would also be 2 generations newer than yours so I would imagine it would be a pretty big differance. Be warned though, the '03s have a very hard hitting mid range. But if you like wheelies, than you will love it.

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I have a 1999 yz400f. The bike still runs but it is acting funny :p . If i was to go out to the bike i could push the kicker down as many times as i wanted,sometimes it will start and sometimes it takes 30 kicks to get the beast fired up :p , but sometimes the kicker will be stiff and you have to use the correct starting procedure :ride: . I just got the valves done thinking that that would solve the problem....it didnt :p . I am now thinking it could be the rings :lol: ..............please tell me what you guys think. :applause::lol::p

I assume something's changed from before; it's not starting the same? My '99 has always needed the "correct" procedure (per the owners manual) to consistently start it. If I just go up and try to kick it, no way! (Well, maybe if I'm lucky it would start)

Maybe it IS the compression release, like YZMAN400 said . . . but then again he needs help now.;-)

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I had starting problems on my 400 until I went back to the stock Plug. Those fine wire plugs just don't work for me. I can start my bike in my pajamas now.

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This is kind of a compression problem guys. But thanks for the input soo far....any ideas about compression problems. Plug and filter are perfect. The kick starter is sometimes way to easy to push down. Then sometimes its normal.

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Like someone posted above, the decomp mechanism is probably sticking open occassionally for some reason.

The 03 450 is an entirely different beast. Much lighter and faster. I think the hit is very controlable. You said you are just getting into jumping and racing so if you are a beginner than you may be just fine on the 400.

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i cant feel any binding in the decomp lever..................i can put my ear by the valve and hear it click......im just going to take the head off and look at the vavles and rings on the piston...............anything that i should know about in taking the bike apart or is it pretty simple? My timming chain is perfect. How long should it take?

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It's a piece of cake. Just make sure that when you remove your cams that the bearing locks don't fall down into the magneto void. Before removing the head, make sure that all the valves have proper clearance. For a engine to start and run proberly, you need fuel-compression-ignition. You are somehow lacking one of these, preventing engine lite off. I would make sure the obvious thing are explored first.

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I know that we all get out of the habit because it's so seldom necessary, but I'd start by checking the valve clearance. It is, after all, 6 years old, and it might actually need to be adjusted. :applause:

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On these bikes, the comp release has been known to stick at times, then free up again for who knows how long. I would check the comp release, oil it a little with the valve cover off to check the valves and such. Much less involved than taking the whole top end apart. My bike has done this twice, then fixed itself both times. First time put me into a panic till I got some advice from this forum. Good luck.

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I took the bike completly apart.and its clean! But the idiot who did the valves made the intake vavles so tight that i couldnt even get a feeler gauge in there! And the keeper on the midile intake valve broke off and valve is slightly bent and now i need all new valves(im told not just to 1 valve). I think the broken valve spring was the problem to start off (stuct open a lill bit) with because the bike felt the exact same when i got it back just like it when i took it in. Now i doubt if he even checked the valves!!!! You would notice a broken keeper right away when you shim the valves. Well the rest of the bike is fine and piston rings and cylinder are PERFECT. I will never give the bike to anyone else now that i know how simple it is. Should i try and get my money back? And if you live in socal never ever take your bike to AFTERBURNER MX!!!!!!!!!!!!!!!!!!!! THE TECHS(if they even can be called the) HAVE NO FU**ING WHAT THEY ARE DOING!!!!!!!!!!!!!!!!

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that has got to be something sticking on your comp. release, you could buy a hotcam with an auto decomp. on it (about $160) and you wont have to worry with your decomp. lever any more, as for ther top end, it is simple, just make sure you have the clearance on your piston to cylinder checked, I just did the top end on my 99 and had to have the cylinder recoated.

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