Bike Wont Start!!!

[77_YZ_250]

Hey,

I just recieved a yz250 2 stroke from a friend it hasnt run in ages. I took it home checked the plug and cleaned it took the carb off cleaned it all up cleaned the jets floats ec. (it was a mess). Then I took the tank off emptied it out and put new gas in mixed properly with oil.

I then proceeded to take the plug out set it on the block it had the ignition cable hooked up. I kicked it over and it had spark.

Then I proceeded to do a compression test on it I gave it a couple kicks and it said the compression was 90lbs, Is this a bad number???

I currently have all the clutch discs out becasue they are needing to be replaced, and I think the hub as well one of the posts that the stud screws into holding the clutch springs ec. in place is cracked. Its not to majour I can still screw the bolt in and its tight but still its craked and should be replaced.

Anyways so all the clutch discs are out and the clutch springs and plate. I put the cover back on and intstalled the plug back in put the carb back on, hooked up the throttle linkage and the gas lines. I kicked it over to start but nothing happend so I proceeded to kick it over and still NOTHING. It feels extremly wierd as I kick it over but I assumed that was because theres basically no clutch in it.

Would not having the clutch in the bike enable it to not start???? or do I have another problem here??? ANY SUGGESTIONS OR HELP WOULD BE GREAT!!

 

[mathd]

i would check the reed valve, these can make a bike hard to start, and 90lbs of compression sound low, this can also make it hard to start.

i would make sure the carb/float bowl if filled with gaz before to attemp starting it.

For the clutch, i assume that if when you kickstart it the piston/cam turn/rev and the spark plug do spark it could run.

 

[77_YZ_250]

i would check the reed valve, these can make a bike hard to start, and 90lbs of compression sound low, this can also make it hard to start.

i would make sure the carb/float bowl if filled with gaz before to attemp starting it.

For the clutch, i assume that if when you kickstart it the piston/cam turn/rev and the spark plug do spark it could run.

Well I checked the reed valves. from what I can tell they look perfectly fine there all laying completly flat and there sealing, and there not seized or anything and they have good flexibillity

Now for the compression im thinking about order all the gaskets and tearing the motor down and putting in new piston rings, head gasket, base gasket ec. BUT how do i know what to torque everything down to when putting it back together?? will iI have to buy a service manual or is there a general rule for 250's ????

 

[mathd]

a service manual will help for the torque and for alot else.
if you dont whant to spend on one, you can take note of how much torque you used when you remove the bolt/screw.. But you wont regret getting the service manual, even if its just for the top end. it tell what to check for when rebuilding, assembly/dissasembly proceedure, what to change etc.

What years is this yz250? maby the service manual as availlable for free download on internet if the bike is not too old...

 

[kawraper]

correct me if im wrong but good compression is 170psi+ .

 

[GarbatyA4]

correct me if im wrong but good compression is 170psi+ .

I believe you hit it spot on.

I compression tested my bike in the winter time... 0 degrees celsius and I got 190 PSI.


Dude, somethings not sealing or you need a new top end.

 

[77_YZ_250]

yea I was just tlaking about it with my frined a few minutes ago. We came up with the idea that maybe the piston rings are stuck or something cause it has sat for years not fogged or bin turned over. oh well guess we wont know till I tear it down. Il keep you all posted when i get it apart i will post pictures.
Thanks for al lyour ideas and help.

 

[GarbatyA4]

good luck man

 

[77_YZ_250]

Alright I just got home and decided to tackle teardown of this motor. What is really intriguing when I opend the head the cylinder walls were extremly clean even though this bike has bin siting AGES not foged or bin turned over. After a little investigating there was no ridge on the cylinder wall (as in wear) I could see the piston ring around the piston at the top it looked liek it was sealing. I then proceeded to remove the block/piston cylinder off, once this was off the cylinder wall looked amazing the piston had no holes, pits dents chips the rings wernt siezed or worn they compress properly. Now im not really understanding HOW this bike could only have 80lbs of pressure :S Here are some photos.

 

[77_YZ_250]

ok I cant seem to add anymore photos I have some of the Cylinder wall and the piston but all are in GREAT condition

 

[coombzy2009]

the cylinder bolts 40lb and head 20lb torque..

 

[jsantapau]

quite possible whatever oil that was left in the cylinder got thick and glued the rings down(lack of better words) also possible is that over the years the rings lost their tension, not really sealing against the wall ,allowing compression to get past the ring /wall as opposed to compression getting behind the ring to help push against the wall.

as for torquing bolts without a manual there is a standard torque value for standard hardware. most head bolts are not standard but a stud with a standard nut would be.
8mm threads I beleive are between 18-24 ft lbs dry

 

[jsantapau]

the cylinder bolts 40lb and head 20lb torque..

ooops I should of read the whole thread