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Okay so I have a 2003 XR250r that hasn't been running in like 5 years. Don't know anything about the bike because I just acquired it a few weeks ago. Cleaned carb, air filter, changed oil. It's getting spark and gas and fires. Seems like the compression is kind of low but starts up when you get it to TDC at kick it hard. Any ways my main problem is the bike will crank for about 3-5 seconds and bog down and cut off. Then it has a hissing out of the exhaust pipe for like 10 seconds that gradually runs out. It like it's the compression running out of the exhaust. I've adjusted all valves in spec and adjusted the decompression where no valves are hung open and put it in time. Pulled the head and didn't find anything abnormal with gaskets or any contact with piston. Is it normal for them to his like that? Do I have a fuel problem? Ive never had a bike blow out so much pressure from exhaust and if stopped running. Any answers to this because it is boggling me? Thanks so much

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Also was about a 1/4 quart of oil in the valve train when I pulled valve cover. I dumped all over the floor. Is this normal?

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yes there should be oil in the valve train.

the head gasket is meant as a one time use, it's supposed to be replaced when the head is removed. the valve cover gasket can be reused.

how did the jets look when you cleaned the carb? could you describe your cleaning method in more detail?

the exhaust headers have copper crush washers to seal to the head that should also be replaced if removed.

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I took carb apart and removed all jets and went through with carb cleaner and guitar string. Carb should be good... what my main question is is why does it cut off and have the existing compression in the cylinder blowing out muffler? 

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I'm grasping here, but have you checked the cam timing with the crank timing? There is a T and F mark on the flywheel as well as two other marks. Could the previous owner have put the bike together out of time?

FYI use the T mark on the flywheel and align the cam index marks level with the head surface

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I don't think 1/4 qt of oil in the valve train is normal.

You need to remove the fuel(pilot) screw and clean that passage. It won't do any good that the jet is clean if the fuel screw passage is gummed up. Be careful in removing it that you account for its spring, washer and oring.

Did you have to make any adjustments to valve clearances? If so, by how much were they off? If they were off by more than a few thousandths, that's a sign you might have been at TDC on the exhaust stroke instead of compression stroke.

If the engine comes to rest anywhere in the compression stroke and you have a leaking valve, you could hear hissing from the exhaust as compression bleeds off. I would make sure you did the clearances right and get it running. It having sat for so long, it may work itself out.

I'd change the spark plug too.

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Wonderspoon... I guess it's a possibility but hasn't been apart since assembled so idk... but yes everything was in time.

Ryder... ya sorry forgot to say that all passages were also soaked and blown up and moved to factory settings. Even tried to turn mixture screw out two turns.

Now with timing it was wired... I put it at TDC and had to loosen intake and exhaust like three turns. But still fired. After thinking I might be 180 out I adjusted them again making sure of compression stroke by putting straw in spark plug. Valves in spec after confirming so I did have it TDC first time also.

Ya I removed head and performed leak down test and they are seating properly and rebounding fine.

I talked to a mechanic yesterday and he said he had Yz250f with hissing and dying out and said it was crack in piston, fixed piston and rings and was fine. Doesn't make any sense but whatever... lol

Also here is a pic of the oil in valvetrain. This is just what spilled out on floor after I took cover offIMG_0131.JPG

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Ok, so you "were" on the exhaust stroke when you first adjusted them. Putting a straw in the spark plug hole doesn't tell you if it's on the compression stroke, only that the piston is at the top of the cylinder, which happens at both the compression and exhaust strokes.

So once figuring out you might have been 180 out, you went around 1 rotation on the crank, back to TDC and was able to reverse those 3 turn adjustments you made previously, until the valves were in spec, right?

I guess we have different notions of what 1/4qt is. lol

Yeah, a crack or hole in the piston would cause a hissing too.

Edited by Trailryder42
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I am not sure... I'm thinking I adjusted them on the exhaust strokes. Would it even start and run for a few seconds if I did this? What is the easiest way to tell you are on compression stroke and at TDC to adjust valves without taking cover off?

And the amount of oil in picture doesn't look abnormal?

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19 minutes ago, Westhall55 said:

I am not sure... I'm thinking I adjusted them on the exhaust strokes. Would it even start and run for a few seconds if I did this? What is the easiest way to tell you are on compression stroke and at TDC to adjust valves without taking cover off?

And the amount of oil in picture doesn't look abnormal?

It sounds over simplified, but for future reference, when setting the engine to TDC on the comp stroke, just remove the valve caps, reach in with your fingers and see if you can feel wiggle in all 4 subrocker arms. If you're on the exhaust stroke, they will be tight, no wiggle or slop at all. Taking out the plug helps prevent the crank wanting to roll past TDC. If you do roll past it, turning it only CCW of coarse, do not roll it back CW to put it on TDC, as that can activate the auto decomp on the right exhaust and throw off your measurement/adjustment. You have to go around 2 more times.

As for the oil amount, it's probably fine.

 

Edited by Trailryder42

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So this is probably why they were really tight because I was on the exhaust stroke? Would me doing this cause the symptoms I'm facing? So now I guess I'll loosen them up all the way and put it at TDC on on compression stroke and adjust. Do you think me doing this would cause the loss of compression and compression coming out of the exhaust?

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7 hours ago, Westhall55 said:

So this is probably why they were really tight because I was on the exhaust stroke? Would me doing this cause the symptoms I'm facing? So now I guess I'll loosen them up all the way and put it at TDC on on compression stroke and adjust. Do you think me doing this would cause the loss of compression and compression coming out of the exhaust?

https://www.rickramsey.net/XR250R.htm

 

There is a procedure for checking your valves near the bottom.

Edited by Wonderspoon

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Just take the plug out and stick a screwdriver in the hole. When it pokes up its furthest...then you're at TDC

Yes but could be compression or exhaust... got the TDC part

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