Dirtbike won't start backfires also

R

Ryan Matz

Member
Oct 7, 2019
4
3
I have a 2012 Yamaha yz250f someone plz help me i recently took apart my cylinder head down to the piston but didn't mess with the piston what so ever i put everything back together the way i was supposed to but when i tried to start the bike it wouldn't start and back fires occasionally

new spark plug gets spark
timing is on
carb is getting fuel
although there is no compression
 

truespode

Moderator / Wheelie King
Jun 30, 1999
7,980
249
Check the valve clearances and make sure you put it at TDC when you put everything back together. Having the cams not aligned or valves that are out of clearance can cause these type of issues.
 
R

Ryan Matz

Member
Oct 7, 2019
4
3
truespode said:
Check the valve clearances and make sure you put it at TDC when you put everything back together. Having the cams not aligned or valves that are out of clearance can cause these type of issues.
Click to expand...
i have made sure about the tdc so maybe it's the valve clearance i will check up on that
 

The Redrider

Member
Jun 14, 2019
238
32
Grab a shop manual and re check everything.
During rebuilds, you must always install fresh gaskets on everything you rebuild...
 

The Redrider

Member
Jun 14, 2019
238
32
Ryan Matz said:
yup did exactly that ordered full top end gaskets and use me the manual the whole time
Click to expand...
Compression release is or should be on your handle bar, it opens up a port in the cylinder head to release the compression on thumper for easy kick starting. If its stuck open like during a rebuild or not set up correctly then it will act like it has no compression. Check to be sure it is installed correctly. Make sure your timing chain and sprockets are set up correctly. Then you should be ok. manual is very important here...
 

truespode

Moderator / Wheelie King
Jun 30, 1999
7,980
249
The 2012 should have an auto compression release and not a cable. Can't remember the specifics but it will be in the shop manual in the area of re-assembly of the top end.
 

The Redrider

Member
Jun 14, 2019
238
32
truespode said:
The 2012 should have an auto compression release and not a cable. Can't remember the specifics but it will be in the shop manual in the area of re-assembly of the top end.
Click to expand...
Well hell man, old xr's, xt's, dr's and klx had em, these new fangled bikes dont have em? I'll be dipped in sheep s___, Lol!
 
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