Please Help With YZ250 trouble

[Elkaholic11]

I just got a 1991 yz250, it's my first bike! I new it had problems when I got it but I figured I could learn by fixing it. I have recently rebuilt the top end, I got the cylinder bored .20 over and replaced the powervalve and all the seals and gaskets. Now that I got it back together all I can do is get it to idle for maybe a minute or so. After it dies there is oil all over the control arm spitting from the exhaust. Does anyone know what the problem is and how to fix it? Thanks for the help.

 

[Elkaholic11]

Please help

 

[John Cena]

Does it have a clean air filter?

What jets are in the carb?

Have you checked the crankseals? If the crank seals are gone you might be able to tell by taking off the startor cover, see if theres any gas/oil in there.

 

[Elkaholic11]

The air filter is a brand new presoaked filter, I'm not sure what jets even are in the carb, Im new to this. I took the starter cover off and there is no oil or gas in there,

 

[showtime586]

After it dies there is oil all over the "control arm" spitting from the exhaust. Does anyone know what the problem is and how to fix it? Thanks for the help.

Do you mean swing arm?

 

[Elkaholic11]

Yeah swing arm sorry,

 

[dc1130]

need more info whats your comp. how long has it been sitting could be crap gas in the carb, wrong jetting, air leak (crank seals),

 

[ls1cameric]

need more info whats your comp. how long has it been sitting could be crap gas in the carb, wrong jetting, air leak (crank seals),

My buddy bought a older YZ250 last week and it ran like crap for 30 seconds and died. Took us an hour to get it started again and this time it ran 4 5 minutes. (This was before he bought it). We got it home and it wouldnt start for anything. we put new gas in it and noticed that it was pouring strait out of the carb drain tube when we turned the gas on. took the carb off because I was thinking the float was stuck. put it back on and wasnt leaking but wouldnt start either. Carb off again and this time we cleaned it w/ carb cleaner. Put it back on, primed the cylender and fired right up.

From what your saying, it sounds like it's either the jetting or the gas. Put some new gas in it and then clean the carb to start. If that doesnt work. Play with the jetting and you should have a fix.

 

[kimoajaj]

I assume that you have tried another spark plug?.
Dirtbikes foul plugs like hell if they aren`t jetted correctly.

What happens if you touch the throttle?.
Normally a bike will have to idle a few seconds before it will respond to the throttle.
Try removing you spark plug and kick it over, see if it spits oil/gas out of the spark plug hole.
To find air leaks, use starter gas, however it`s hard if the bike won`t run at all.
If you spray onto the flywheel while the engine is running, nothing should happen, if it tends to rew or the idle becomes different when you spray, then the crank seal is blown.
If there is lot`s of oil in your crankhouse, then it could be the right side seal.
I`m not sure, but try smelling your sparkplug after having kicked the engine over a few times, transmission oil has a totally different smell from two stroke oil. It`s hard to know the difference if your not used to it, but just grab som cans and smell the difference.

Who knows, maybe you could figure it out this way. However, might be very hard to smell if gas as mixed into the oil. Could fool you. Well, it was just a tip.

Do you know the history of the bike?.
The bike should fire up and run even if the jet`s arent perfect. Ofcourse if they are WAY off then it wount run, but who would install jets that are way to big, I wouldn`t.

Good luck

 

[cal9126]

do you have to split the cases to replace the cranks seals.....

 

[Elkaholic11]

I'm almost positive that you have to split it to change the seals, do you think that bad seals could be my problem?