yz250h won't start or fire.

[cleopatrisha]

my 81 yz250 will not even fire. here what I know for sure. the carb is good because I tried it on another bike, the spark plug has nice blue spark set at .025 , timing mark is at tdc, the spark plug gets wet with gas, feels like it has good compression, I have not inspected the reeds yet, they looked ok when looking in from intake boot. but if the spark plug gets wet it should at least fire, backfire, anything. one thing I just thought of, does this bike have a woodruff key? if it does and it gets sheared will it still have spark? thanks for any advice.

 

[Big Bore Stroker]

If the flywheel key was sheared it would still have spark just at the wrong time.

 

[cleopatrisha]

I don't think it is sheared if my timing marks line up with top dead center consistintly.

 

[IndyMX]

Just because your reeds looked good from the boot end, doesn't mean they are not trashed.

remove and inspect.

 

[cleopatrisha]

Bike does fire when I pour a little gas directly into spark plug hole. the only thing I notice with the reeds is a couple of the petals have a slight stick when I initially push on them with my finger to open them. other than that they look good not warped or cracked.

 

[IndyMX]

You probably won't be able to see if they are sealing against the reed block, from the boot side..

 

[2 strokes for life]

cleopatrisha, possibly run a comp test to find out. Also, replace the reeds in that old of a bike. You might want to also set the float level.

 

[originaldirt]

I believe that the correct timing is before top dead center (BTDC) and not at Top dead center (TDC). If you are not technically checking the timing correctly, it may not fire.
OriginalDirt

 

[2strokerfun]

Indeed. No engine will run corrrectly with spark firing at true TDC. Now, you may indeed have timing marks aligned correctly, I don't know. But if you actually have it firing TDC, the spark is too late. By the time anything is ignited and burned, the piston is already far along its downstroke. My '76 elsinore 250 is 20 degrees BTDC. Yours should be timed somewhere along those lines.