YZ250F compression loss

[Pokie]

....attempted to start the bike up for the first time since DirtWeek, but virtual absence of compression! I can crank kickstarter by hand. Compression release seems ok. There was no indication of any problem at the end of my last ride. Unless Billywho snuck into my garage and rode it like he rode thump's at DW'01, I can't figure why the sudden compression loss? (Hey my KX250 started on first kick!)
Anyone experienced similar mystery?
Pokie:ugg:

 

[Seth_88]

Maybe a valve stuck open? I read somewhere about that happening on the 250/426's.

 

[^SQUID^ RACING]

When was the last time that you checked your valves? I'll bet you that they're too tight, and that's causing your sudden loss of compression.

 

[MotoGreg]

I've gotten my YZF severely flooded a few times and when that happens you can kick it right through TDC really easily. The gas washes the oil off of the cylinder wall and then the ring doesn't seal and you have no compression. It's nothing to worry about, just do this... hold the throttle wide open (don't pump it, leave it open) and pull in the comp release and kick it over about 15 times. This clears all the gas out of the cylinder. Then release the throttle and the comp release and just start as normal.

 

[JasonJ]

Yup Yup, I have had the same problem with my WR 440 when th pilot jet is too rich. One maybe two kicks and no more compression, Take the choke off and pull the hot start and you have compression in 2 kicks, let it start with the hot start out and then put it back in. You may need to lean the pilot out if it happens again. Its weird and scared the poo out of me first time it happened.

 

[JasonJ]

Yeah Spode! that kinda happened to me this weekend! I had just changed the oil and wanted to start the bike up to check the level out and all so I put the stock baffel in to be nice to the old people and all, it started first kick, I ran it about 30 seconds at idel and gave it a little rev and shut it down, the oil level was low so I topped it off and went to kick it again and no go, then after like 3 kicks I lost compression, OMG! I was sweating bullets and removed the whole comp release cable from the lever, pulled the spark pug put it all back together and 2 kicks and no comp :eek: . As soon as I pulled the hot start I herd huffing form the carb and got the comp back,,, hmmmm, so I removed the stupid stock butt plug and she lit on the second kick with the hot start out. Just seems like there was a vacume on the intake side not letting the intake charge in, very weird!
Any way the whole episode cost me like 2 hours, LOTS of stress, and like 3 lbs of sweat cause it was unusally hot and I was kicking my B**ls off!

 

[Pokie]

Tried both suggestions....

...but no change in compression! gotta take it to the man!......
clueless in yzf-land...

 

[Rich Rohrich]

Pokie - Before you do anything:
- check to make sure the compression release cable isn't hung up and hanging the exhaust valve open, also check the actuator going into the cylinder head to make sure it isn't damaged and hanging up.
- change the oil
- pull the spark plug and shoot a little oil in through the spark plug hole
- pop the plug back in
- cycle the engine through a couple of times with the compression release pulled in then check for compression.

If none of that works give me a call at home or on my cell tonight.

 

[JasonJ]

Random act of kindness from Rich? Man, I would hate to see the roaming charges for Venus :) . Give him a call Poki, he IS the man.

 

[Pokie]

Rich...thanks...

I'll try those things tomorrow... I had already checked the compression release assembly which seems to be operating properly. Didn't see your post until now as I was at Okie's tonight helping with some home-improvement chores; he had talked to OT who had a similar experience with his 426 and got it going with a push start; we'll try that next...
thanks again, everyone, for your input.

 

[biglou]

Any News?

Did you find out anything yet, Pokie? Inquiring minds want to know!:)

 

[Pokie]

NOTHING YET....

... have been fighting the flu and a nasty cough......... not in the mood to tinker til next week... actually during the night I thought I heard some elves in the garage. Tthey left traces of skin and hair; they must have been scratching their heads too!
Pokie

 

[roosteater]

Originally posted by Truespode
I used to put a butt plug in the exhaust before getting the e-series with the s/a plate.

Ivan

OK........now I know Ivan has been hanging around with Gomer for far too long....what's he doing with a "butt plug" laying around handy?

:eek:

 

[SFO]

I seek enlightenment

I have heard of fuel washing the oil off of cylinder walls and causing no compression?
How come when I assemble my top ends dry they have plenty of compression?
What am I missing?
Where does this fuel wash create no compression? How? Does oil create compression?
I thought that the rings created a mechanical seal...
Ferris?
:eek:

 

[MotoGreg]

We get '96 and newer Civics towed into work all the time for no starts. They crank over super fast with no compression and your first thought is that they broke a timing belt and bent the valves but actually they're just flooded and the gas washes away the ring seal. I just hold the throttle on the floor for max air and keep cranking it... about 20 seconds of cranking and it sputters to life with a ton of smoke out the exhaust.

The same thing has happened to my YZF a few times over the past 2.5 years. I don't know how, maybe someone was twisting the throttle when I wasn't around but the first time I scared the hell out of me. I put a couple squirts of oil down the spark plug hole like you'd do with a car to get the rings to seal, only I found out that without an electric starter that was a BIG mistake. Best to just use the technique I posted above, it works every time, I've had to help people out at the track several times as well that had that problem.

 

[Boozer]

this has been discussed on thumpertalk.com. What has happened to me is when friends whith young kids come around, they go and take a look at the bike, usally without me knowing. Naturally they take a seat and play MX games with it, snapping the throttle as often as possible. So the accellerator pump squirts heaps of fuel onto the piston and there you have it.

 

[Pokie]

THANKS TO OKIE.....

...Okie's magic kick got it going. With less than full compression, found the TDC, no choke, it started on the 4th kick...... running normal now!
thanks