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Wont Start, No Compression...

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good morning TT, first post, long time reader.

alright, ive got my 2008 wr250f that now, after a few touches from my *skilled* hand, will not start, and has absolutely no compression...

this thing ran before i left from deployment, came back, and no joy. but that was expected after sitting for nearly a year. pulled the carburetor out with the mindset that some gas may have been left behind, and after sitting for nearly a year gummed up the jets. so pull it apart, let sit in a bath of carb cleaner and sea foam. put it back together, reinstall, no joy... i was very thorough and very meticulous.

being that i am constantly gone, the bike only has ~300 hours on her, and i bought her new, since my purchase, i had not yet checked the valve clearance, now this is more than i have ever done with a bike, but, i like to think that i have some basic mechanical skills. so with following the manual, i checked 5 valves with the bike top dead center, and as per the manual, the valves are within standards for both the exhaust and intake...

this is the part that makes me cringe, and up until this point it had compression, just would get that bite to start... with everything back together, carb back in, valve cover back on, all back to normal, go to start, nothing...so...i spray some carb cleaner done the intake boot, attempt to start, idles for a moment off of the carb cleaner, then it makes a sound that reminds me of a wet fart, and it let a puff of white-ish smoke, and a flame out of the carb...then no more compression. 👍

while trying to engage the electric start, spins freely all day, no resistance, and while trying the kick start, you can literally turn it over with your hand...

took it to a shop, did compression test, was told >95% leakage...awesome.

my area of expertise is in aircraft, not 4 stroke, 5 valved, one cylindered motorbikes...i have bitten off more that i can chew and am desperate for help. i know i screwed up big, but where?

a hole in the piston? an intake valve that is still open letting the combustions as well as the compression leak through?

i would like to try and fix my self, both for funds, and pride. any ideas, i have not torn it open yet since then, been about a week since the drama unfolded, i had some 'business' to attend to in southern california, im now home again and ready to tear into it.

i just have to convince the girlfriend to let me breakdown a motor in the livingroom, no more garage :ride:

thanks alot guys :worthy:

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One time back in the day, I had a 1982 Yamaha XT-200J (4-stroke dual-purpose bike) that I rode everywhere since it was my only street transportation.

It ran perfectly for a solid year of constant use.

When I finally bought a truck to drive on the street (and haul my other bike, a 1983 YZ-125K with), I abruptly parked the XT for about 5 or 6 months.

One day, when I decided to ride it, the second kick of the kickstarted resulted in no compression - the piston rings suddenly stuck in their groves, probably because they were worn, or at least getting there.

Disassembling the engine for new piston and rings took care of that.

Don't know if that's your problem, but, if the bike has 300 hours of use on it, it may be time for some maintinance.

Edited by YZEtc
spellin'

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If it started with carb cleaner then your problem is the carb. Just letting it sit in a bath won't cut it. Replace the pilot jet and use compressed air thru all the passageways. That lack of compression you feel is probably a combination of the auto-decompression and paranoia.

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Swede, what about the compression test that read with a 95% leak, and the flame that shot out of the carb? like i said i am no professional, but, im sure that you dont what flames coming from the intake side.

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If it had no compression it wouldn't start at all. Get the carb cleaned out really well and go from there. Make sure the accelerator pump is working and use the choke. The flame shooting back is prolly just from the carb cleaner. You can't really use a standard compression gauge on these bikes because the auto decompression cam bleeds most of it off. To troubleshoot no compression you need to use a leak down tester.

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I have had cars especially, but most recently my XL600 lose compression after sitting due to valve stems sticking in their guides due to sticky deposits.

Honda even had a service advisement at one time about the phenomenon on their cars. The "cure" was to introduce while cranking the engine, an upper cylinder cleaner. GM cleaner was recommended, but any good one will suffice I have found. They also recommended some sort of upper end cleaner added to the fuel. Techron has proven to be the best there as of my last research.

Yesterday my 600, which hadn't sat that long failed to have full compression. I figured it was a sticky valve like in the cars. I was able to get it to start, luckily, and after shutting it off after riding the kickstarter would stop at TDC as usual.

Worth a try before teardown for sure.

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