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WReckless

Lost All Compression

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I just got a call from a friend of mine,who stores my bike for me, and he went out to start the bike...and it just kicks through. Its a '99 wr 400 that has been sitting for about 2 months. I had been saving up for a dampner and tires,sprockets,fork seals and chain. The bike started three weeks ago to be moved and has not been ridde since. I am hoping the compression relaese is just stuck? But i don't know how to test for it. If it is rings ,worst case, what will I need to do to upgrade to 426. I was told be a freind just the barrel needs to be changed. Any help would be great. Ihave the factory manual to use when testing but, I just need to know where to start. He also told me that after kicking it thru the bike had a large puddle of fuel under it.

I'm going over there after work tonight to get a first look at it. What do i need to look for?

THANKS WRECKLESS

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No tension on decomp lever. Try bumpstarting it. This happened to a friend of mine on his 98' YZ400, ended up starting to push the thing out of the woods after 30 mins of trying to figure out what was wrong with it. He got to a down hill and figured he'd try bump starting it. Well, whatever he did fixed it. The compression came back and the bike ran great till he sold it months later. Our thoughts were, like yours, the decomp valve was stuck.

Good luck, let us know :applause:

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My 426 does that every once in a while, usually after sitting for a couple weeks in cold weather. In fact it happened yesterday after sitting since the middle of November. I just kick it until it starts. After it warms up, compression always returns. It could be some carbon on a valve that is keeping it from closing completely. When I put my bike away after riding I put the piston at TDC so all the valves are closed.

KC

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thanks, for the info i'll try that tonight! i hope it'll be that simple i had the engine rebuilt about 6 months ago.

hopfully i can :applause: soon. I will post back up in the am since i don't have a pc at home

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He snuck it out for a spin and (((popped))) the motor? :applause:

i hope not he has roommates but i don't know if they could start the bike

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took it down to the frame to inspect comp release put it back together

bump started it down a large hill. stayed running then i stalled it and it would not hold idle any ideas?

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Bump Start Down A Long Hill Finally Stayed Running On Third Try

But Then I Stalled It At The Bottom The Hill And Could Not Get It To Idle With Out Help From Throttle

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I got this from another website. This is what you need to go to 426.

YZF & WR 400

These first-generation F's can be easily upgraded to 426cc with stock Yamaha parts -- or to 440cc's with the parts listed, plus our 2.0mm stroker listed above.

One weak point on the 400 is the smaller piston pin. Upgrading to the 426 parts gives your engine better reliability for the same (or cheaper) prices than purchasing these parts aftermarket.

You can have your 400 cylinder bored and re-nikasiled, but this process typically costs more than the $250 you'd pay for a new 426 cylinder!

To rebuild your 400 to a 426, you will need to purchase the following from your Yamaha Dealer:

Qty

Part Number

Description

Price

Total

5BE-11681-00-00

YZF 400 CRANK PIN

$31.67

$31.67

93310-634B0-00

YZF426 CRANK BEARING

$44.14

$44.14

5JG-11651-00-00

YZF426 ROD, CONNECTING

$50.96

$50.96

5JG-11631-10-00

YZF426 PISTON (STD)

$134.96

$134.96

5JG-11603-00-00

YZF426 PISTON RING SET (S

$27.28

$27.28

5JG-11633-00-00

YZF426 PIN, PISTON

$11.49

$11.49

93420-19084-00

YZF426 CIRCLIP

$0.15

$0.30

5JG-11181-00-00

YZF426 GASKET, CYLINDER H

$33.50

$33.50

5BE-11351-00-00

YZF426 GASKET, CYLINDER

$5.01

$5.01

5JG-11311-00-00

YZF426 CYLINDER 1

$245.37

$245.37

Total

$584.68

Prices are quoted from Yamaha of Troy (February 2004) and are subject to change.

Your 400 crank will need to be rebuilt with the new 426 rod and needle assembly. You can have a local shop do it, or order our 440cc kit above, and we'll take these parts and make your 400 a 440!

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I used to have the same problem with my 99 400 and it happened a lot during the winter. It was the valves sticking open a bit. The valve springs are pretty light and it doesn't take much to hang up the valve. If the bike has been sitting for a while condensation could cause surface rust to form on the valve stem (or maybe even the face of the valve and seat) and keep it from closing fully.

I have the same problem with a slightly different cause. My valves freeze open. Condensation freezes on the valves and the ice holds them open. This was happening weekly to me and I'd have to let the bike thaw out in a heated space. The ice would melt and compression would come back. It wasn't a big problem but was a pain.

When it happened during summer after sitting, it took a while for the valves to fully seat. I kicked for a while and gradually the compression came back, but even after it started and ran for a few minutes it wasn't perfect. I'd have to ride around slowly feathering the gas to keep it running until the valves fully loosened up.

The cure was to set the bike to TDC when I shut down so the valves are closed. If ice or surface rust forms on the stems while the valves are closed it's not a problem since they're forced open mechanically but the cam. I guess it gets scraped off by the valve guide as they open. I haven't had a valve hang up on me since I started shutting down at TDC.

I have had valves freeze open while running in extreme cold and lost compression while driving. Same cure, heat the engine, melt the ice, full compression restored.

It is also possible that the piston may have tapped a valve and bent it if it was stuck open far enough when you were kicking over the engine. Once I felt the piston touch the valve when I tried to kick over the engine. Luckily it didn't bend but it is definitely possible.

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I just got a call from a friend of mine,who stores my bike for me, and he went out to start the bike...and it just kicks through. Its a '99 wr 400 that has been sitting for about 2 months. I had been saving up for a dampner and tires,sprockets,fork seals and chain. The bike started three weeks ago to be moved and has not been ridde since. I am hoping the compression relaese is just stuck? But i don't know how to test for it. If it is rings ,worst case, what will I need to do to upgrade to 426. I was told be a freind just the barrel needs to be changed. Any help would be great. Ihave the factory manual to use when testing but, I just need to know where to start. He also told me that after kicking it thru the bike had a large puddle of fuel under it.

I'm going over there after work tonight to get a first look at it. What do i need to look for?

THANKS WRECKLESS

can't tell what is the reason, but seems like happends to me to, 3 months ago.

you can read about it at one of my threads (first one).

the problem at my bike was stacking bucket (valve push) at the cylinder head bore. (happend because excessive heat of the head that distorted the bore).

the solution was to polish the bore with sandpaper mesh 600 with the finger.

i probably removed 2-3 hundreds of mm, until the bucket could rotate smoothly in the bore.

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When's the last time you checked your valve clearance?

That's were I'd start.

Then I'd look at the intake rubber. (Did you find out where the gas is coming from?)

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no signs of exhaust or intake leaks. engine was rebuilt about 9 months ago.

valve clearance should be fine.(i hope!)

i'm gonna change the jets and some other parts to night and we'll see where we are then. hopin to be in jawbone this weekend! :applause:

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no signs of exhaust or intake leaks. engine was rebuilt about 9 months ago.

valve clearance should be fine.(i hope!)

i'm gonna change the jets and some other parts to night and we'll see where we are then. hopin to be in jawbone this weekend! :applause:

check you spark plug first, if it is loosen or brake, compression can leak through their.

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Mine does the same thing once in a while, but it is for gasoline entering the cylinder and washing out the oil on the ring of the piston, loosing that way the seal and compression,,, but once i manage to start it, the compression comes back.

Never forget to close your fuel knob after each ride.

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Mine does the same thing once in a while, but it is for gasoline entering the cylinder and washing out the oil on the ring of the piston, loosing that way the seal and compression,,, but once i manage to start it, the compression comes back.

Never forget to close your fuel knob after each ride.

TAHNKS btw i love that avatar! :applause:

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