What would cause a spark plug to not fire under compression?
I have a 1994 kdx200 and it wont start. I have fuel and air. And the plug will spark out of the cylinder but I cant get the bike to start. The only thing I can think of is that the plug isnt firing in the cylinder or that the engine is flooded. If the plug wont fire under compression what would be the reason for that?
Ok, you say the plug will fire out of the cylinder.
What color is the spark? Blue, white or yellow?
It needs to be Blue as anything else indicates other issues.
If the color is wrong then either you have excess resistance in the plug wire/boot or you have dirty commections or a rusted ground. If all those look good then you need to do an OHMs reading on the primary and secondary of the coil. If those read good then you need to look at the stator and do the OHMs readings there and also check for rust on the flywheel magnets or on the trigger coil.
If all that checks out then you may just be flooded with excess fuel mix settled in the bottom of the crank case and it will have to be cleared to get the plug to fire.
FYI: You will need to refer to the service manual for the correct OHMs readings for you system.
It does require a certain amount of voltage to jump that gap under compression. You can remove the plug, attach your meter to the primary coil leads and kick the bike over. You should usually be getting over 45v for most bikes.
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