Yz450 oil on my spark plug

SOURCE: YZ 450 STARTING PROBLEM

Hi and welcome to FixYa,

Offhand, the backfire is significant. It indicates that fuel is getting inside the combustion chamber and it further confirms that there is spark. Being the case, it would appear that this is now a timing issue. A couple of ideas to explore:

• compare the original stator coil and the uprated one; are the coil location on the same side, on the same angle, on the same distance from the edge;
• there would be a guide notch on the base plate of the coils, are they identical and does it fit exactly back into position;
• there would be a guide/lock pin that keeps the magneto/flywheel in position;
• there would be timing marks on the magnet/flywheel that must coincide with marks on the engine case.

SOURCE: YZ450 only starts when pushed started, once on header get's RED

Your carb needs cleaned. Primary circuit or choke circuit are blocked. When you push start your bike and jump on it first reaction is to twist throttle. after it runs for a while the fuel mixture is incorrect and will make it run lean/rich which in turn heats motor up. I would guess rubber seal in choke circuit is stuck. If you clean carb it should solve your problem. Good luck and have a good ride.

SOURCE: while riding my yz 125 it just died and won,t kick up again

• If a hole in the piston then install new piston and rings. Next, clean the carbon off the head and install a new head gasket.
• If cylinder wall is scared the piston has seized up. Pull the cylinder off and take it to the dealer. Have them bore the cylinder and return it along with a new oversize piston and rings.
• While at the parts counter, get a new stock spark plug and a supply of Yamalube Two Stroke Motor Oil. You need to add 4 ounces per gallon when filling up. This will be a 32/1 gas to oil ratio. NEVER ride the bike without at least the needed 32/1 mix.

Ned C Cook

• 3433 Answers
• Posted on Nov 03, 2009

SOURCE: 2006 yz 450 very hard to kick will not start,got

Ignition timing sounds over advanced.

gavin jones

• 1508 Answers
• Posted on May 23, 2010

SOURCE: 04 yz 450 backfires and is hard to start when is c...

Runs better with choke means the mixture is lean,
Has the exhaust been changed.?
Did this problem just begin.?
Check for air leaks on intake manifold.
Clean carb.
Check valve clearances
raise the needle jet one notch
one size up in the main jet.

check one item at a time, and write notes about jetting changes.and improvements
I also run Moreys upper cylnder lube, helps starting hot or cold, and helps stop "cough stopping" with heavy rear brake use